An H8 Badge for VCFMW

[Lee Hart]

Let's start a new thread, as we were wandering off-topic in the VCF-East thread.

I'm thinking of making a wearable "badge", intended as an inexpensive kit for people to build at VCFMW in September. It would introduce people to the Heathkit world of kit-building. Here's a "straw man" description.

- 80C85 CPU (since this is a *vintage* computer show)

- 32k RAM at 8-40k

- 32k EPROM, 0-8k with PAM8 (or hex version?), 40-64k with Benton Harbor BASIC

- bit-banged serial port using the 80C85's SID and SOD pins.

- 4x4 keypad using tactile switches

- nine 0.3" 7-segment LED displays.

- a PCB styled like a half-size H8 front panel (about 6"w x 3"h)

- powered by USB-serial adapter, or battery operated with three AAA cells.

- a manual to imitate the Heathkit manuals (probably online to download).

- target parts cost around $20.

I've been scribbling circuits, and think I can do it with about six chips.

- 80C85. OKI seems to be the best source of these on ebay.

- 27C256 EPROM (cheap and easy to get).

- CY7C199 32k "skinny" RAM (because I use them in my other kits).

- 74HC151 address decoder (a 1-chip way to get the funny address map).

- 82C55 to provide three 8-bit I/O port (LED anodes, LED cathodes, read keypad).

- 74LS145 to select LED cathodes and keypad rows.

PAM-8 and BHBASIC would have to patched to run in this minimalist H8 environment, as the keyboard and display mapping won't be the same. Likewise for the bit-banged serial port. I'm guessing BASIC could be stored in high EPROM, and block-moved into RAM to execute. There should be lots of room in high EPROM for other programs as well (like the iconic "your H8 is up and running" demo).

This is just my "brainstorming" so far. I'm not a software guy, so I'll certainly need help to pull this off. Can you help, or think of any improvements? Please let me know what you think!

Lee Hart

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[Joseph Travis]

It's very likely that only the PAM8 monitor ROM will have to be modified for I/O as BHBASIC would be doing it's console and keypad I/O through the ROM.  We'll have to verify that though.  Seems to me there are a couple qwerks about BHBASIC when it starts up... I'll look into it.

Joe

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[Douglas Miller]

I'll throw in my "free" software advice. The 8085 SID/SOD as serial does not make a good console. The challenges of receiving characters asynchronously (unexpectedly, as required for typing) requires near-constant CPU monitoring of SID. If it is only used for output, say a printer, that is easier to manage (XON/XOFF handshake is  still a challenge).

[Randy E (OoMOR)]

Lee/All,

Would these badge kits be available to those of us that can't make it to VCFMW?

Thanks, Randy

[Lee Hart]

Doug: I agree that SID by itself is not a responsive serial input. The program would have to be looping on a RIM instruction to keep reading SID to detect a START bit.

However, the serial input can also be wired to trigger an interrupt. Josh Bensadon did this on the software for my Z80 Membership Card and 8080  Altaid kits. The program can then be doing anything. When a serial character comes in, its START bit sets SID low *and* triggers an interrupt. The interrupt handler reads the bits on SID (ignoring further interrupts). When finished, the interrupt handler puts the character in a buffer, enables interrupts, and returns to the main program.

Randy: Yes, of course they would be available to anyone that wants one. Like Norberto etc. do with their boards, I expect that we'd try to get some idea of how many PCBs and parts to order. They'd get sold on a first-come first-serve basis. If there was enough interest, we could make additional batches.

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[Douglas Miller]

I think the results will still be unsatisfactory, especially in an H8 environment where you have interrupts occurring frequently (2mS clock) and that could delay the response to the START bit resulting in framing errors. Plus, you can't be sending characters and still receive characters at the same time (full duplex not supported, due to 100% CPU consumption required each for sending and receiving), further degrading the experience. I urge caution against expecting SID/SOD to work well as a general purpose serial port.

[Lee Hart]

Doug, take a look at Josh Bensadon's code for my 4 MHz Z80 Membership Card. It's at http://sunrise-ev.com/photos/z80/ZMCv15.zip. He implemented a full duplex interrupt-driven bit-banger 9600 baud serial interface, while also running a 2 msec clock interrupt. It can send and receive at the same time without missing characters.

The serial input interrupt has the highest priority. When a START bit arrives, it stops the 2 msec clock, and reads the serial input character. If a serial output character is already in progress when the START bit arrives, it finishes sending it while reading the serial input character. It works quite well as a console for running CP/M.

Josh wrote similar code for my Altaid 8800 with its 2 MHz 8080 CPU. It's at http://sunrise-ev.com/photos/8080/altaid05.asm. It also has a 2 msec clock and serial input interupts. The code is a little less ambitious due to the lower performance of the 8080, but it still works well enough for running CP/M.

Given that we're talking about a "toy" H8 and not the real thing, I think it can work well enough. At least I'm willing to give it a try. :-)

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[Douglas Miller]

Hmm, the ZMCV15 code uses an 8250 UART, but does bit-bang an SPI port for SDCard access (not the same thing). It does do some bit-banging using a spare bit on the 7-segment display, but that leverages the display refresh code and hardware. The altaid05 code looks to be half-duplex. I have my doubts, but best of luck.

[Joseph Travis]

I remember Josh's work on bit banging the serial I/O for the Z80 Membership Card and believe the serial I/O via SID/SOD will work fine but, you'll probably want to select the CPU XTAL frequency to accommodate the various baud rates.  I also started thinking about the "your H8 iS UP And running" demo and believe it uses direct I/O with the front panel and would have to be rewritten for the H8 Badge.  I still have to investigate using BH BASIC (tape version).

Joe

On Sat, May 2, 2026 at 3:17 PM Douglas Miller <durga...@gmail.com> wrote:

Hmm, the ZMCV15 code uses an 8250 UART, but does bit-bang an SPI port for SDCard access (not the same thing). It does do some bit-banging using a spare bit on the 7-segment display, but that leverages the display refresh code and hardware. The altaid05 code looks to be half-duplex. I have my doubts, but best of luck.

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[Bob Bell]

I have been following this thread with interest; I always wanted an H8, but could not afford one.

IMO, you'll bypass the headache with SID/SOD for serial I/O by just including a hardware U/ART, such as the TR1602 or similar.

I used this U/ART on my SERCON board a few years ago. No initialization needed.  It just works the way you set it's configuration pins.

Bob Bell

[Douglas Miller]

Seems to me that a very simple H8-like machine would be nice. Display and keypad to simulate the front panel, minimal RAM and ROM, no HDOS or CP/M support. The 8085 SID/SOD could be implemented as a download/upload channel, something like the cassette interface or to load/save Intel HEX format programs. An expansion bus then to add additional hardware in the future. Connecting the SID/SOD to a USB-Serial dongle (also supplying power) would then allow connecting to a PC for download/upload. I'm not sure how BHBasic would work over that serial connection, but with an expansion bus you could add a regular UART. Of course, the SID/SOD interface would never work with existing software that expects an 8250 UART.

[Lee Hart]

Here's a (preliminary) schematic of what I have in mind. Eight ICs on a 3" x 6" PCB. I tried, but couldn't get it any less.

- 2 MHz 80C85, 32k RAM, 32k EPROM, add. latch, addr.decoder, 82C55 I/O ports, digit select, and 4053 for "glue" logic.

- Memory map has 0-2k and 40-64k ROM, 2k-40k RAM.

- RAM is battery backed up.

- The 9-digit display is similar to the H8 (same segment and digit assignments).

- I kept the RUN and PWR LEDs; the rest are not relevant on an 80C85.

- The keyboard setup is quite different. It's multiplexed with the display, but the same 0 + RST keys will reset the 8085.

- I used an 82C55 to get three parallel ports for the I/O.

- SID and SOD for a serial port. SID is tied to RST7.5 for fast START bit detection.

 There are a few "Hartian" design choices to save parts that bear explaining.

I used a 4053 triple SPDT analog switch to implement the needed "glue" logic. U8A is wired to chip-select the 82C55 when IO/M=1 and A7=0. U8B copies the RST-/ key to be in series with the 0-key (so both keys have to be pressed to Reset). U8C is wired as an inverter, so the high "idle" state of a TTL serial input sets interrupt RST7.5 low.

The "beeper" is just a piezo disk on an output bit. Software will have to toggle it high/low to make a sound. This should be possible if it's inverted each time the next LED row is selected every 2 mSec.

The "timer" is just an RC network using the RST5.5 interrupt. When the next LED row is selected, also set PB6 high. C5 is charged by R8 until RST5.5 reaches its trigger voltage. The interrupt sets PB6 low (to discharge C5), then selects the next LED row and sets PB6 high again. 

The battery backup diodes switch the ground end of the RAM. That's so when VCC goes to zero, the RAM's VCC=0 and its VSS is the negative battery voltage. That makes all the RAM's inputs (especially /WE) all at VCC (i.e. "high").

I'm not planning to run HDOS or CP/M on it. Just the monitor, (hopefully) BHBASIC, and maybe other programs from the cassette days. There's lots of room in the ROM to store various demo programs that can be block-moved from high ROM into RAM to run. There are four unused I/O bits, which could conceivably be used to bank-switch a larger RAM or ROM.

The interrupt setup is completely different, but the source for PAM8 is available so it could be modified to run. BHBASIC is more of a problem; it's probably doing direct I/O and I don't think the source is available.

Parts cost looks like about $20-$25, and I think it will all fit on a 3" x 6" PCB.See anything wrong?

See anything wrong? Or anything that could be improved?

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On Sun, May 3, 2026 at 12:44 PM Douglas Miller <durga...@gmail.com> wrote:

Seems to me that a very simple H8-like machine would be nice. Display and keypad to simulate the front panel, minimal RAM and ROM, no HDOS or CP/M support. The 8085 SID/SOD could be implemented as a download/upload channel, something like the cassette interface or to load/save Intel HEX format programs. An expansion bus then to add additional hardware in the future. Connecting the SID/SOD to a USB-Serial dongle (also supplying power) would then allow connecting to a PC for download/upload. I'm not sure how BHBasic would work over that serial connection, but with an expansion bus you could add a regular UART. Of course, the SID/SOD interface would never work with existing software that expects an 8250 UART.

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[Joseph Travis]

Lee,

Norberto used a small 2KHz buzzer on his Super 89 board design that doesn't require an AC signal to emanate sound. It's available from Jameco and DigiKey: AdaFruit Industries part number 1536 for about $1.25.

Joe

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[Eric Mack]

It’s time to downsize. This system includes software manuals, H14, DC Hayes Modem, and more. Most impressively, it includes Norberto’s CF Memory board.

 

Complete Heathkit H8 Computer. Working, with Software and Peripherals & Modem | eBay

 

Eric Mack

[Douglas Miller]

It might be nice if the ROM could optionally be a 28C256, rather than only 27C256.

[Lee Hart]

I thought of that. But I was thinking it might be more entertaining to have direct control of the speaker bit so you could bit-bang it to play chiptunes. :-)

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[Lee Hart]

I guess I'm "committed". :-) I ordered a batch of OKI 80C85 CPUs, 3x7 segment LEDs, and 32k RAMs for the H8 badge today. An updated schematic is attached. I replaced the triple analog switch with a quad 74HC132 NAND gate. I swapped 82C55 ports A and B so the display row/column address and bit assignments are the same as the H8. The extra gate also provided a 2 msec clock. Only 8 chips!

Software for it will be "entertaining". I can't find an online source for PAM8. Does anyone have it? I do have source for XCON8 but it's a lot more complicated and has a lot of code that would be useless in this project.

Joe Travis also noted that BHBASIC source isn't available, and it has embedded I/O code that won't be present in the badge. Anyone have any ideas for workarounds?

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[Douglas Miller]

I'd ask again that you add jumpers so that the 28C256 can be used instead of the 27C256.

I'll also echo what Joe said. Bit-banging the speaker to implement the H8 "horn" is going to seriously cripple software. The H8 turns on/off the "horn" in the 2mS interrupt handler, and so it takes no overhead - does not steal cycles away from anything else. bit-banging both speaker and serial port is going to make for some challenges.

[Joseph Travis]

Attached is a reconstruction of the XCON8 ROM Monitor source code for the H8.  There are some good notes in the file.

Joe

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[glenn.f...@gmail.com]

David Troendle and I did the work to recreate HDOS source in ASM form. It lives on bitbucket (David’s preferred repository):

https://bitbucket.org/HeathkitGuy/sebhcsoftware/src/master/HDOS/HDOS2.0/

 

I believe for what’s posted there we assembled the code and compared to the original ABS files and found either no differences or differences only in uninitialized storage.

 

We also did BH BASIC but I don’t see it posted on the site. Perhaps we never came full circle and completed that. I have a work in progress version on my computer. The files are dated June 2019 so it’s been a while!...

 

• Glenn

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[glenn.f...@gmail.com]

If you do the bit bang on the speaker make it compatible with the mod that was popular back in the early days. Basically instead of gating the 1Hz tone the mod lets you gate the speaker directly. Of course this takes all of the cpu when you do it. The programs are on HUG volume 1

 

 

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Lee Hart
Sent: Tuesday, May 5, 2026 4:19 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

I thought of that. But I was thinking it might be more entertaining to have direct control of the speaker bit so you could bit-bang it to play chiptunes. :-)

 

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[Eric Mack]

Guys, now that my H8 system is sold and shipped, I have two floppy drives and a drawer full of new 5.25" and 3.5" floppies all DSHD. Any Interest? As for the drives, I have one Tandon TM-100-2A and One Toshiba MKM 0202A 001 drives.

 

 

Eric Mack

[Lee Hart]

Consarn that H8! I just realized that its LED segments have *three* inversions, not two. A LOW data bit lights a segment. My current design has a HIGH light a segment.

This inversion seems like a biggie. I can add an octal inverter; but every extra part makes it bigger, more expensive, and will take longer to build (creeping featuritis). On the other hand, every deviation from the original means more H8 software won't work without modifications.

It seems like the only programs that will run without patches are ones that strictly call routines in the ROM (so the ROM entry points can be written to work the same as an H8). Any thoughts?

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[Lee Hart]

Thanks Glenn. I'll look up the speaker mod and see what it did, and whether it would work on the mini H8.

Hopefully BHBASIC would only need patching in its I/O routines. Please let me know if you find your source!  

As for HDOS running on this mini H8: Man, that's a stretch! I suppose I could use a flash ROM, like the Microchip 512k SST39SF040 (about $4 from Newark). It could simulate a disk drive. Jon Chapman used it on his Glitch Works 8085 SBC, which runs CP/M with it.

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[Douglas Miller]

My 2 cents is to keep it simple and don't try to make it run HDOS or CP/M - at least not without an expansion bus/board. But allowing a 28C256 instead of 27C256 is important. The 7-segment inversion is problematic, although if existing code depends on the ROM to do the actual refresh then the ROM could invert the data before sending to the 8255. The keypad scanning is not software compatible anyway, and I don't believe the ROM provides any general purpose "keypad input" routine.

Providing a way to download programs will be valuable, although the bit-bang SID input will need to ensure it can process each character in the limited time available between the last bit being detected and the next START bit - less than 1.5x bit rate (slower baud means more time to process).

[Dave McGuire]

Eric, I'd be interested in picking those up from you for LSSM, if
they're still available.

-Dave

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Dave McGuire, AK4HZ
New Kensington, PA

[glenn.f...@gmail.com]

So as I said, I do have the source for BH BASIC (110.06.00) – as distributed with HDOS 2, it may still have some typos from the OCR process but could presumably be repaired, but it makes extensive use of HDOS (SYSCALL) and not just for I/O. making it a ROMable or stand-alone version would be non trivial.

 

IMO more useful would be an earlier version from the “Tape OS” era. We have those in executable form and that may be enough?  My understanding is the source was available for this way back when but I’m not aware of any accessible copy on any of our servers (though I recall someone here saying they had it).

 

I agree that running HDOS on this system would be a stretch. Stick to the early era of software…

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[Eric Mack]

Hi Dave,
I'm giving them to Norberto

Eric Mack
Founder, Speaker, Consultant
Click here to schedule an appointment.

Eric...@IntentionallyProductive.com
(661) 242-8410
linkedin.com/in/EricMack
Deliver your best with calm and clarity.

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From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Dave McGuire
Sent: Wednesday, May 6, 2026 1:07 PM
To: se...@googlegroups.com

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[Lee Hart]

> I'd ask again that you add jumpers so that the 28C256 can be used instead of the 27C256.

Douglas, I like this idea! But the 28C256 is an expensive part (Digikey lists it for $11.62). I wonder if a flash ROM might be a better choice? For example, Digikey has the Microchip SST39SF020A-70-4C-PHE (a (256k x 8 32-pin DIP) for $3.36. The 4 unused bits of the 82C55 could be used for the extra address lines (A15-A18).

> I do have the source for BH BASIC (110.06.00) – as distributed with HDOS 2... IMO more useful would be an earlier version from the “Tape OS” era. 

Herb Johnson sent me a link to a PDF of this BASIC source. I looked, and agree that it would be a big problem to use it without HDOS. The earlier tape-based 4k BHBASIC should be easier to adapt, if the source can be found.

PS: Today's little additions to the schematic were to add pullup resistors to /WR /RD and IO/M as these pins get tri-stated during Reset.

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[Douglas Miller]

Oh, I see, eliminate the 27C256 entirely and replace it with a larger flash device. I see that the DIP32 versions of SST39SF020/SST39SF040 are discontinued (or soon will be), but I guess one can get a PLCC adapter and use PLCC32 ones.

[Lee Hart]

I'm not sure I can get the 040 chips, or what they'd cost. But it's possible. :-)

The memory mapper provides 32k of ROM and 32k of RAM. There are 4 unused outputs (PC0-PC3), so that could address 16 banks of 32k = 512k. But I'd kind of like to keep a spare output bit to change to an org.0 memory map. Maybe PA4 could be used for that, since there is no single-step circuit?

I'd rather avoid surface-mount parts if we expect hobbyists to build it.

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On Wed, May 6, 2026 at 9:10 PM Douglas Miller <durga...@gmail.com> wrote:

Oh, I see, eliminate the 27C256 entirely and replace it with a larger flash device. I see that the DIP32 versions of SST39SF020/SST39SF040 are discontinued (or soon will be), but I guess one can get a PLCC adapter and use PLCC32 ones.

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[Douglas Miller]

PLCC are not surface mount, but their sockets do have pins in a denser arrangement. Not that bad to solder, IMHO. The 040 parts are possibly cheaper than 020. In keeping with most storage, the larger devices quickly become the normal and thus cheapest, and both have been around for some time now.

The problem with bank selecting is that you need to provide some mapping where the code being executed at the time banks are switching does not get switched. And ORG0 introduces a new complexity to the mapping. At the very least, you probably want to use a GAL/CPLD for the memory mapping/address decoding, but not sure what size you'll need to support the mappings you need.

[Lee Hart]

Hi Douglas. Sorry for the pause. I've had some health issues. But I've also had time to think. :-)

This mini-H8 is intended to introduce people to Heath and kit-building, so KISS is the name of the game. I'd like to get at least a basic "toy" ready for VCFMW, but allow for expansion. Through-hole is desirable, as even a PLCC socket is difficult to solder. But Flash ROMs are still available in DIPs. The 040 seems to no longer be available, but the 010 and 020 aren't too expensive or hard to find (yet). They could be a cheap / easy way to provide "disk" storage.

Here's my thought: As you suggest, provide ROM socket jumper options for a 32k 27C256 EPROM (cheapest base model), 64k 27C512 EPROM (not much more) or 128k SST39SF010 flash ROM (for a write-able "disk"; $2.89 from Digikey, but last time buy is 7/1/26).

Then I can provide two memory maps:

1. ROM at 0-8k, RAM at 8-40k, ROM at 40-64k (the setup in my last schematic). Similar to H8 at power-up or Reset. The upper ROM could imitate a disk drive. It could theoretically run HDOS, though I'm not enough of a programmer to do it.
2. Org.0 with RAM at 0-32k, ROM at 32-64k. This could theoretically run CP/M. I can use bit 4 in the digit select port which is currently unused. (It was the H8 INT20 single-step interrupt). Looking back at my schematic, bit 4 can be tied to the D0 input of address decoder U5. A resistor can pull it high on power-up or Reset to put ROM at 0-8k, and bit 4 can be set low to put RAM at 0-8k the D0 input of the U5 address decoder. The unused bits PC0-PC3 can be the extra address lines for larger ROMs.

Yes, bank switching like this can really be messy software-wise! But I've done it on my Z80 and 8080 membership cards. The program that's switching banks just has to be in RAM when you "blow up" the ROM!

I'll post a new schematic when I get this entered.

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On Wed, May 6, 2026 at 9:47 PM Douglas Miller <durga...@gmail.com> wrote:

PLCC are not surface mount, but their sockets do have pins in a denser arrangement. Not that bad to solder, IMHO. The 040 parts are possibly cheaper than 020. In keeping with most storage, the larger devices quickly become the normal and thus cheapest, and both have been around for some time now.

The problem with bank selecting is that you need to provide some mapping where the code being executed at the time banks are switching does not get switched. And ORG0 introduces a new complexity to the mapping. At the very least, you probably want to use a GAL/CPLD for the memory mapping/address decoding, but not sure what size you'll need to support the mappings you need.

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[Douglas Miller]

Best of luck. I think some of those things are more complicated than they seem. If it were me, I'd focus on making the best platform for your original intent - a miniature bare-bones H8 with a way to be able to upload/download small programs from a PC (as if it were a cassette). I think HDOS, ORG0, and CP/M just unnecessarily complicate the whole thing. In my opinion.

[Lee Hart]

I agree. The rev. version is sure to be bare-bones, as that's all I'm likely to be able to do myself in time for VCFMW.

But jumper options and bigger parts cost nothing if not populated.

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On Mon, May 18, 2026 at 6:31 PM Douglas Miller <durga...@gmail.com> wrote:

Best of luck. I think some of those things are more complicated than they seem. If it were me, I'd focus on making the best platform for your original intent - a miniature bare-bones H8 with a way to be able to upload/download small programs from a PC (as if it were a cassette). I think HDOS, ORG0, and CP/M just unnecessarily complicate the whole thing. In my opinion.

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[Lee Hart]

Hi all,

I've been having some health problems, which slowed me down. But here is an updated schematic for the mini H8.

- added jumper options so it can use anything from a 27C256 32K EPROM to a 39SF040 512K flash ROM.

- added battery backup for the RAM.

- org.0 switching so the first 8K can be RAM or ROM (so could theoretically run HDOS or CP/M).

- a 2 mSec clock on RST7.5 (the only 8085 edge-triggered input).

- serial using SID and SOD pins.

- serial input also triggers a RST6.5 interrupt to avoid missing Start bits.

Though drastically simplified (only 8 chips), I *think* it should be able to accurately emulate a real H8. But since the I/O is different, I'm sure a lot of H8 software will need patches to run on it. Does anyone know how many programs talk directly to I/O, versus ones that stick to monitor calls?

[Bob Bell]

Lee,

Sorry to hear of your health problems and pray you are on the mend.  I have been there, done that several times now too.

I have been mostly lurking on this thread since you started it.  As a builder of many Heathkits, most still functioning here in my office/shop, I always wanted an H8, but never had the $$ at the time.  So I am keenly interested in this project and will most likely buy from you when they are ready, assuming the plan is to make bare boards available to the community like many do over on the S100Computers group.

My question to you as I look over your schematic: What EDA software are you using?  Is it KiCAD?

I really appreciate your logical layout of the schematic.  It is very readable, well documented, and easy to follow unlike the schematics for some of the modern S-100 boards that have been created in the past 20 years where components are just plastered on the sheet with connections by netname only and little explanation of function.  That method leaves one wondering how it works.

I posted a comment some time ago in regards to the serial I/O.  I still think a real SIO chip would be welcome by many.  I know you want to keep the first version very simple, but maybe just add a header with all the bus signals, so perhaps a daughter board could be added in the future to accommodate the SIO and other add-ons.

Thanks for what seems like a very worthwhile project!

Bob Bell

To view this discussion visit https://groups.google.com/d/msgid/sebhc/CAF__8hc_E4A7oZF-FgaVfeTiRV4WtS8sW_ACXFDxfAYu5YFH3w%40mail.gmail.com.

[Joseph Travis]

Hi Lee,

I've given this some more thought over the weekend.  Due to the I/O differences between this project and the original H8, it looks like the monitor ROM will be a complete rewrite.  We can double up on the SID/SOD ports, using it for both console and tape I/O.  The unfortunate thing is that many H8 tape programs won't work because they use direct I/O but, you'll be able to create, dump and load new programs the same way it was done on the H8.

Are you going to implement a SD interface similar to the Z80 Altoids computer?  I'm thinking that we may be able to boot CP/M with a proper BIOS and possibly HDOS 3.0 as well (not HDOS 2.0 or 1.5).  HDOS 3.0 has an external console driver (TT.DVD) that could be rewritten for SID/SOD and the SY.DVD would have to be written for the SD card.  Of course the monitor ROM will need to have the necessary code to boot from the SD.

That's my thoughts for the moment.  BTW - I hope that you are feeling better soon!  Oh, just one more thought... In order to reduce / minimize confusion, you might want to change the name of this project to H8.5 which gives a nod to both the H8 and the 8085 CPU?  'Just a(nother) thought.

BR,

Joe

To view this discussion visit https://groups.google.com/d/msgid/sebhc/06f885c2-6af9-4ba6-b875-8d894a089dd2%40gmail.com.

[Lee Hart]

I've made a few small additions to my mini H8 schematic.

- I changed the SPST power/standby switch to a SPDT switch, so the Standby position grounds the RESET line to the 8085. This should stop it from going "nuts" and writing nonsense to memory as it shuts down.

- I added a jumper option so memory from 0-8K can be set for either RAM or ROM at power-on or RESET. It obviously needs to be set to ROM initially. But since RAM is battery backed up, a program in RAM (like CP/M) could be executed immediately. This also provides a path to initialize a new flash ROM without a programmer.

Bob, I use OrCAD SDT386 for my schematics and PCB layouts. It's an old DOS program from 1996. It's powerful and extremely fast on modern hardware. I particularly like that it is keyboard-driven (no mouse and menus needed).

Joe, I've started looking at the XCON8 source, and I agree it needs to be extensively rewritten. But I still don't know what entry points in it should be kept the same for external programs. I guess time will tell.

I can include an expansion connector to add a UART or SD-card. But it's so small that H8 or even H89 I/O cards would dwarf it. They would probably be on a new PCB. I could rework my Z80-SIO card to work.

I haven't really settled on a name for this little guy. I've been calling it a "mini H8", but that can change. Any ideas? "H8-5" sounds like an accessory card for the H8.

Now... Onward to see if I can layout this little darling!

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[Joseph Travis]

Hi Lee,

I believe the entry points you are looking for are actually part of the H17 boot ROM.  They should be referenced in the ASM / ACM files included with HDOS.

BR,

Joe

To view this discussion visit https://groups.google.com/d/msgid/sebhc/CAF__8hdfhk-Ls8AnMManWNEG1eCMHK%2BHKzGbrU6KBPTxLmQbrg%40mail.gmail.com.

[Douglas Miller]

There are definitely some "entry points" in the main ROM that were used (I won't comment on that practice, but you can guess my thoughts). I tried to preserve those in my new H8/H89 monitor ROM, they are marked by conditionals that check the addresses. I'm by no means certain I've got them all, but so far there haven't been any complaints. See https://github.com/durgadas311/MmsCpm3/blob/master/rom/newmon/src/h8core.asm

On Wednesday, June 3, 2026 at 7:22:24 PM UTC-5 Lee wrote:

...

Joe, I've started looking at the XCON8 source, and I agree it needs to be extensively rewritten. But I still don't know what entry points in it should be kept the same for external programs. I guess time will tell.

... 

[Glenn Roberts]

Right. MTR.ACM as I recall? Perhaps another?

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[Lee Hart]

Greetings, kit-fans. I have (slowly) continued working on the mini H8. I settled on a circuit, and managed to lay out a PCB. It's 5.7" x 3". I used 0.015" minimum trace widths and spacings, 0.060" minimum pad sizes, and did not run any traces between pads on the solder side. This is about twice the size of most modern boards, which should make it easier to solder.

To get the small size, I resorted to a few tricks. I used SIP resistors,  and put the 0.3" wide ICs under the 0.6" wide ones. If the CPU, ROM, and I/O chip are in socket strips, it leaves room for the others underneath. I also made room for a USB serial converter.

I ordered some boards last week. Picture attached. If anyone wants one to help with the project, let me know!

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[Joseph Travis]

It looks awesome Lee!  Please post a schematic.  Thanks!

BR,

Joe 

To view this discussion visit https://groups.google.com/d/msgid/sebhc/CAF__8hexPse4PaBiK9yxs1VSwGPMhne0%2BjDTGORDe0QBMK5Jjw%40mail.gmail.com.

[norberto.collado koyado.com]

As, always a beautiful layout and pcb. Congratulations!

Norby

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From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Joseph Travis <jtravi...@gmail.com>
Sent: Monday, 06 July 2026 10:17:18
To: se...@googlegroups.com <se...@googlegroups.com>

Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

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[Lee Hart]

Thanks, Joe! The schematic is barely changed from the earlier version. I only rearranged the SIP resistor and quad NAND gate pins to simplify the PCB layout.

BTW, the PCB picture was JLCPCB's check plot. For some reason, they always show my NC drill file upside down. So I laboriously deleted all the holes. In doing so, I mistakenly deleted the "." key label. Here is an updated version with that fixed. I should also note that I slightly edited the key labels, hopefully to make them more understandable (like STEP instead of SI).

Also... Does Darrell or anyone familiar with 3D printing know if some kind of overlay can be made to provide labeled keycaps? "Naked" tactile switches are a pain to use for extended periods. Is there a flexible plastic that could have all 16 keys with little "hinges" so they can flex?

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[Lee Hart]

Thanks! Your boards are wonderful works of art, and you're far more prolific than I am. I'm very s-l-o-w at it, but managed to achieve all my "stretch" goals. I included the batteries, US adapter, and piezo speaker, and still kept it small.

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[Mike Cassidy]

Lee

I’d be interested in giving this a try.  Send details on the board. 

Mike 

Regards,

Mike Cassidy

To view this discussion visit https://groups.google.com/d/msgid/sebhc/CAF__8hexPse4PaBiK9yxs1VSwGPMhne0%2BjDTGORDe0QBMK5Jjw%40mail.gmail.com.

[norberto.collado koyado.com]

Thanks Lee!  The only small boards, I have done are the "RCBus-80pin” to run the H89 monitor on it. 

I think to keep the battery supplying VCC, it will be nice to add the 5V Step-Up Voltage Regulator U3V9F5 which will provide VCC with a battery input of 2.6v. The user could run longer the CPU with such regulator. 

On the 82C55 you want to use OKI "MSM82C55A-2”  as it can operate at 3V.

Norberto

[Lee Hart]

Norberto>  On the 82C55 you want to use OKI "MSM82C55A-2”  as it can operate at 3V.

Good point. The OKI 82C55 is the only one whose datasheet explicitly says it works at 3v. The parts I have are Intersil, but work down to at least 3.5v. I have OKI MSM80C85A CPUs, which are also spec'd to work at 3v.

I didn't think of including a 3v-to-5v switching regulator. (I'm too olde-skool I guess.) It would allow use with a single 3.7v lithium cell.

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[Lee Hart]

Progress report: I got my mini H8 PCBs last friday, and have been building up the first one. Testing as I go. So far, so good. I'm using socket pins for the 0.3" wide ICs that hide under the 0.6" ones, so everything is socketed for troubleshooting. Will post photos when I finish getting it built. :-)

[norberto.collado koyado.com]

Great work!👍

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From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>

Sent: Tuesday, 14 July 2026 10:38:49

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[Lee Hart]

Thanks Norberto. :-) Here is a "baby" photo of the first assembled PCB. I left out the 0.6" chips so you can see the parts underneath. The white connector is for a CH340 USB-serial adapter. There is also a place for a Sparkfun FTDI USB-serial adapter (they have different pinouts).

There is no software (yet). I'd be glad to send one to anyone who would like to help write it. My plan is to start with Heath's PAM8 and modify it for the I/O changes.

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[norberto.collado koyado.com]

It looks great. On the middle battery, I think you will need to add Velcro underneath, so it doesn’t elevate from the pressure of the other two batteries. Perhaps it might not be an issue, but just in case.

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From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>

Sent: Saturday, 18 July 2026 16:54:21

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[Joseph Travis]

'Looks awesome Lee!

To view this discussion visit https://groups.google.com/d/msgid/sebhc/CAF__8hfJLSTqSWgcJA%3DpGjt2S_GyHXywUDmCfSOvwJGSC9Atqg%40mail.gmail.com.

[Randy E (OoMOR)]

Lee,

That looks really nice. Thank you for doing this.

Randy

[Lee Hart]

You're right; the center cell does need support. I have a plastic battery tube salvaged from something. But the plan is to suggest wrapping the cells with a strip of paper glued or taped to form a tube. Here's a photo of the board with the batteries and 0.6" ICs installed.

Now the fun begins.😀 My first test will be a program that just echoes the SID input to the SOD output to confirm that it works.

I made up some parts kits, and will be sending them out on Monday to people that requested one to help with development.

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[norberto.collado koyado.com]

Board looking great. Do you think the display will drain the battery very fast?

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From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>

Sent: Sunday, 19 July 2026 14:05:44

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[Lee Hart]

I'm guessing it will indeed have a relatively short battery life. LED segment current is designed for about 3ma. If half the segments are lit, that's about 30 segments or 100mA. The rest of the circuit draws 29mA at 5v, so the total load is about 130mA. AAA cells are good for around 500mAH, which is around a 4-hour battery life.

But I imagine most people will mostly use it with a USB adapter supplying 5v power (especially once we get HDOS or CP/M going).

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[ocl...@earthlink.net]

Hi again Lee

 

Regarding “(especially once we get HDOS or CP/M going)”, I hope that having the H8 BASIC is still something that is planned. I imagine that being able to play with the computer in BASIC will be more immediate and accessible than anything in C/PM. I suppose it comes down to what the most likely use of a “badge” computer would be.....fairly brief playing and demonstrations, or getting real work done......

 

Paul

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Lee Hart
Sent: Sunday, July 19, 2026 6:22 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

I'm guessing it will indeed have a relatively short battery life. LED segment current is designed for about 3ma. If half the segments are lit, that's about 30 segments or 100mA. The rest of the circuit draws 29mA at 5v, so the total load is about 130mA. AAA cells are good for around 500mAH, which is around a 4-hour battery life.

 

But I imagine most people will mostly use it with a USB adapter supplying 5v power (especially once we get HDOS or CP/M going).

 

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On Sun, Jul 19, 2026 at 5:04 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:

Board looking great. Do you think the display will drain the battery very fast?

 

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From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>
Sent: Sunday, 19 July 2026 14:05:44
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

You're right; the center cell does need support. I have a plastic battery tube salvaged from something. But the plan is to suggest wrapping the cells with a strip of paper glued or taped to form a tube. Here's a photo of the board with the batteries and 0.6" ICs installed.

 

Now the fun begins.😀 My first test will be a program that just echoes the SID input to the SOD output to confirm that it works.

 

I made up some parts kits, and will be sending them out on Monday to people that requested one to help with development.

 

Virus-free.www.avast.com

 

On Sat, Jul 18, 2026 at 8:55 PM 'Randy E (OoMOR)' via SEBHC <se...@googlegroups.com> wrote:

Lee,

 

That looks really nice. Thank you for doing this.

 

Randy

 

On Saturday, July 18, 2026 at 5:57:08 PM UTC-7 Joe Travis N6YPC wrote:

'Looks awesome Lee!

 

On Sat, Jul 18, 2026 at 7:54 PM Lee Hart <electr...@gmail.com> wrote:

Thanks Norberto. :-) Here is a "baby" photo of the first assembled PCB. I left out the 0.6" chips so you can see the parts underneath. The white connector is for a CH340 USB-serial adapter. There is also a place for a Sparkfun FTDI USB-serial adapter (they have different pinouts).

 

There is no software (yet). I'd be glad to send one to anyone who would like to help write it. My plan is to start with Heath's PAM8 and modify it for the I/O changes.

 

Virus-free.www.avast.com

 

On Tue, Jul 14, 2026 at 5:49 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:

Great work!👍

 

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From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>
Sent: Tuesday, 14 July 2026 10:38:49
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

Progress report: I got my mini H8 PCBs last friday, and have been building up the first one. Testing as I go. So far, so good. I'm using socket pins for the 0.3" wide ICs that hide under the 0.6" ones, so everything is socketed for troubleshooting. Will post photos when I finish getting it built. :-)

 

On Wed, Jul 8, 2026 at 3:01 PM Lee Hart <electr...@gmail.com> wrote:

Norberto>  On the 82C55 you want to use OKI "MSM82C55A-2”  as it can operate at 3V.

 

Good point. The OKI 82C55 is the only one whose datasheet explicitly says it works at 3v. The parts I have are Intersil, but work down to at least 3.5v. I have OKI MSM80C85A CPUs, which are also spec'd to work at 3v.

 

I didn't think of including a 3v-to-5v switching regulator. (I'm too olde-skool I guess.) It would allow use with a single 3.7v lithium cell.

 

Virus-free.www.avast.com

 

On Wed, Jul 8, 2026 at 2:54 AM norberto.collado koyado.com <norberto...@koyado.com> wrote:

Thanks Lee!  The only small boards, I have done are the "RCBus-80pin” to run the H89 monitor on it. 

I think to keep the battery supplying VCC, it will be nice to add the 5V Step-Up Voltage Regulator U3V9F5 which will provide VCC with a battery input of 2.6v. The user could run longer the CPU with such regulator. 

On the 82C55 you want to use OKI "MSM82C55A-2”  as it can operate at 3V.

To view this discussion visit https://groups.google.com/d/msgid/sebhc/CAF__8heqLAVrWKYah5McfHodOAC6j4tuoyHX-nQuLW0c4e4Phg%40mail.gmail.com.

[Douglas Miller]

The LED display is multiplexed, right? So battery life will be better than calculated for segments lit continuously.

[glenn.f...@gmail.com]

We may be able to do some clever tricks to automatically dim or disable LED update

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Douglas Miller
Sent: Sunday, July 19, 2026 7:50 PM
To: SEBHC <se...@googlegroups.com>
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

The LED display is multiplexed, right? So battery life will be better than calculated for segments lit continuously.

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[norberto.collado koyado.com]

Lee, if you still have any left blank pcb's, I would like to get one along with the BOM to get buy the parts.

[Douglas Miller]

My point being, if each segment draws 3mA and there are 30 segments lit across 9 digits, and each digit is on 11% of the time, then that would be about 10mA total for the display. Unless I've missed something critical.

[Lee Hart]

Norberto (and Glenn): I'd be glad to send you a PCB, but I'm not sure I have your current address. Can you send it to me at <leea...@earthlink.net>?

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[norberto.collado koyado.com]

Done.

Thanks Lee!

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>
Date: Monday, July 20, 2026 at 6:51 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

To view this discussion visit https://groups.google.com/d/msgid/sebhc/CAF__8he%2BT_YBqR2wSV9iBZJZF-jDvVvu2FKomEpLFZ6647GJeQ%40mail.gmail.com.

[Lee Hart]

Douglas, I think you're right. I forgot that the multiplexing will lower the total LED current, so it won't be as bad as my off-the-cuff estimate.

The high-state output resistance of the 82C55 is about 100 ohms. The LEDs have about a 1.8v forward drop. The 74LS145 has about a 0.5v drop. So the LED current is about 5v-1.8v-0.5v, so 2.7v / 100 ohms = 2.7ma. But only one digit is "on" at a time. Half the segments would be 2.7ma x 4 = 11ma.

When spread across 9 digits, I'm wondering if I may have a problem with not enough brightness.

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[Lee Hart]

The keys on the mini H8 are on 0.4" centers. Paul Schmidt is working on some 3D printed keycaps for it. I seem to recall that someone made replacement keycap stickers for the H8. They would be 0.4" square and could be used for the mini H8. Does anyone remember who made them?

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[Douglas Miller]

I think you'll need to experiment and see. As I recall, our eyes (brains) tend to alter how we perceive pulsing light sources vs. steady ones, and so the perceived brightness may not be (as bad as) the expected 1/9. At one point, early in the days of multiplexed displays, there was a lot of research done on this (I think). I seem to recall some articles on that, as people were trying to figure out how to make digital displays "optimal".

On Tuesday, July 21, 2026 at 3:49:01 PM UTC-5 Lee wrote:

...

[ocl...@earthlink.net]

Hi Lee

 

I did a little bit of planning work on the H* keycaps. Had quite a headache for most of the last few days, so did not feel much like doing anything, but better today.

 

I have a few questions and observations on the subject of the keypad labels.

 

• I pulled out my H8 from storage, and indeed the labels measure somewhere between 0.4” and 0.41”; I suspect that the recessed keytops are actually right at 0.4”, as you said, and that the larger dimension is measurement error,
• That said, the keytops that I am designing will be smaller than 0.4” square. If they were exactly 0.4”, none of the keys would push, due to friction with other keys on 0.4” centers. So, any repro key labels that might turn up from somebody will require at least some trimming to fit the new 3D printed key caps, so no extra hardship for me to design my own laser-printable key cap label artwork, which would also need to be cut out. People making the kit, if they want to use key caps, could go either way on which labels to use.....EXCEPT some artwork on 0.4” square labels might be too close to the edges and thus might end up being cut off during trimming.
• I compared the PCB silkscreen legends with the label artwork on my H8. Some disparities I need your help with:
• S7 label says “SI” while the silkscreen says “STEP”.....the latter will fit, but I wonder if your version might do something else as noted by “SI”....?
• SP label says “REG”, but the silkscreen is blank in this regard......is this function not likely to make sense/be implemented?
• SM (?) label says “MEM” at the upper left and “RTM/0” at the lower right, but the silkscreen says only “MEM”......?
• SR label says “ALTER” at the upper left and “RST/0” at the lower right, but the silkscreen says only “ALTER”......?
• I am doing some experiments with different adhesives for the labels. I usually use Scotch Extra Strength adhesive roller/tape runner, which is truly strong and permanent. I am also trying Scotch Permanent Glue Stick, and CA glue. The glue stick has the advantage of being briefly repositionable during the first few seconds, but it is intended for paper and does not grip plastics nearly as well.

 

I hope to finish the 3D design and print the first experimental samples tomorrow.

 

Paul

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Lee Hart
Sent: Tuesday, July 21, 2026 4:37 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

The keys on the mini H8 are on 0.4" centers. Paul Schmidt is working on some 3D printed keycaps for it. I seem to recall that someone made replacement keycap stickers for the H8. They would be 0.4" square and could be used for the mini H8. Does anyone remember who made them?

 

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On Tue, Jul 21, 2026 at 3:48 PM Lee Hart <electr...@gmail.com> wrote:

Douglas, I think you're right. I forgot that the multiplexing will lower the total LED current, so it won't be as bad as my off-the-cuff estimate.

 

The high-state output resistance of the 82C55 is about 100 ohms. The LEDs have about a 1.8v forward drop. The 74LS145 has about a 0.5v drop. So the LED current is about 5v-1.8v-0.5v, so 2.7v / 100 ohms = 2.7ma. But only one digit is "on" at a time. Half the segments would be 2.7ma x 4 = 11ma.

 

When spread across 9 digits, I'm wondering if I may have a problem with not enough brightness.

 

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On Mon, Jul 20, 2026 at 11:30 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:

Done.

 

Thanks Lee!

 

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>
Date: Monday, July 20, 2026 at 6:51 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

Norberto (and Glenn): I'd be glad to send you a PCB, but I'm not sure I have your current address. Can you send it to me at <leea...@earthlink.net>?

 

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On Sun, Jul 19, 2026 at 8:57 PM Douglas Miller <durga...@gmail.com> wrote:

My point being, if each segment draws 3mA and there are 30 segments lit across 9 digits, and each digit is on 11% of the time, then that would be about 10mA total for the display. Unless I've missed something critical.

On Sunday, July 19, 2026 at 6:50:01 PM UTC-5 Douglas Miller wrote:

The LED display is multiplexed, right? So battery life will be better than calculated for segments lit continuously.

On Sunday, July 19, 2026 at 6:22:38 PM UTC-5 Lee wrote:

I'm guessing it will indeed have a relatively short battery life. LED segment current is designed for about 3ma. If half the segments are lit, that's about 30 segments or 100mA. The rest of the circuit draws 29mA at 5v, so the total load is about 130mA. AAA cells are good for around 500mAH, which is around a 4-hour battery life.

 

But I imagine most people will mostly use it with a USB adapter supplying 5v power (especially once we get HDOS or CP/M going).

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[Glenn Roberts]

IMO the SI (single instruction) and REG (register) labels are important and should be retained. The RST/0 and RTM/0 refer to the two-key combination actions (the subject key and the ‘0’ key) for either resetting the system or returning to the PAM monitor. They are both important functions but if space does not allow perhaps they could be omitted from the labels

Once you have a 3d model to share I’m happy to print some keycaps and experiment. I’ve had good luck with the Brother pTouch labeled printer for such things…

Sent from my iPad

On Jul 22, 2026, at 12:14 AM, ocl...@earthlink.net wrote:



Hi Lee

 

I did a little bit of planning work on the H* keycaps. Had quite a headache for most of the last few days, so did not feel much like doing anything, but better today.

 

I have a few questions and observations on the subject of the keypad labels.

 

• I pulled out my H8 from storage, and indeed the labels measure somewhere between 0.4” and 0.41”; I suspect that the recessed keytops are actually right at 0.4”, as you said, and that the larger dimension is measurement error,
• That said, the keytops that I am designing will be smaller than 0.4” square. If they were exactly 0.4”, none of the keys would push, due to friction with other keys on 0.4” centers. So, any repro key labels that might turn up from somebody will require at least some trimming to fit the new 3D printed key caps, so no extra hardship for me to design my own laser-printable key cap label artwork, which would also need to be cut out. People making the kit, if they want to use key caps, could go either way on which labels to use.....EXCEPT some artwork on 0.4” square labels might be too close to the edges and thus might end up being cut off during trimming.
• I compared the PCB silkscreen legends with the label artwork on my H8. Some disparities I need your help with:
• S7 label says “SI” while the silkscreen says “STEP”.....the latter will fit, but I wonder if your version might do something else as noted by “SI”....?
• SP label says “REG”, but the silkscreen is blank in this regard......is this function not likely to make sense/be implemented?
• SM (?) label says “MEM” at the upper left and “RTM/0” at the lower right, but the silkscreen says only “MEM”......?
• SR label says “ALTER” at the upper left and “RST/0” at the lower right, but the silkscreen says only “ALTER”......?
• I am doing some experiments with different adhesives for the labels. I usually use Scotch Extra Strength adhesive roller/tape runner, which is truly strong and permanent. I am also trying Scotch Permanent Glue Stick, and CA glue. The glue stick has the advantage of being briefly repositionable during the first few seconds, but it is intended for paper and does not grip plastics nearly as well.

 

I hope to finish the 3D design and print the first experimental samples tomorrow.

 

Paul

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Lee Hart
Sent: Tuesday, July 21, 2026 4:37 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

The keys on the mini H8 are on 0.4" centers. Paul Schmidt is working on some 3D printed keycaps for it. I seem to recall that someone made replacement keycap stickers for the H8. They would be 0.4" square and could be used for the mini H8. Does anyone remember who made them?

 

<image002.jpg>

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On Tue, Jul 21, 2026 at 3:48 PM Lee Hart <electr...@gmail.com> wrote:

Douglas, I think you're right. I forgot that the multiplexing will lower the total LED current, so it won't be as bad as my off-the-cuff estimate.

 

The high-state output resistance of the 82C55 is about 100 ohms. The LEDs have about a 1.8v forward drop. The 74LS145 has about a 0.5v drop. So the LED current is about 5v-1.8v-0.5v, so 2.7v / 100 ohms = 2.7ma. But only one digit is "on" at a time. Half the segments would be 2.7ma x 4 = 11ma.

 

When spread across 9 digits, I'm wondering if I may have a problem with not enough brightness.

 

<image002.jpg>

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On Mon, Jul 20, 2026 at 11:30 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:

Done.

 

Thanks Lee!

 

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>
Date: Monday, July 20, 2026 at 6:51 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

Norberto (and Glenn): I'd be glad to send you a PCB, but I'm not sure I have your current address. Can you send it to me at <leea...@earthlink.net>?

 

<image002.jpg>

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[Douglas Miller]

I did realize/remember something regarding the display recently. The H8 Front Panel (which includes the 2mS clock) generates a "clear" on the segment refresh register at the end of the 2mS cycle, which effectively blanks the current digit at that time. This means that the software must update the digit/segment select registers "immediately" after the 2mS Clock interrupt signal, after which that digit will be displayed for about 1.5 mS. I think the main reason for this is so if (when) the software crashes - or interrupts get stuck disabled - that the display will go blank. Otherwise, the most-recently refreshed digit will be stuck on. I don't think there's any practical solution here for this hardware, but it's just some behavior to be aware of.

[norberto.collado koyado.com]

The 8085 cannot do single stepping as it does not generate /MI. It requires a GAL, a flipflop and some logic to create single step. The 8080A CPU has that build-in.

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From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Douglas Miller <durga...@gmail.com>
Sent: Wednesday, 22 July 2026 04:32:18
To: SEBHC <se...@googlegroups.com>

Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

I did realize/remember something regarding the display recently. The H8 Front Panel (which includes the 2mS clock) generates a "clear" on the segment refresh register at the end of the 2mS cycle, which effectively blanks the current digit at that time. This means that the software must update the digit/segment select registers "immediately" after the 2mS Clock interrupt signal, after which that digit will be displayed for about 1.5 mS. I think the main reason for this is so if (when) the software crashes - or interrupts get stuck disabled - that the display will go blank. Otherwise, the most-recently refreshed digit will be stuck on. I don't think there's any practical solution here for this hardware, but it's just some behavior to be aware of.

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[Lee Hart]

Douglas, I think the H8 had the LED turn-off hardware because LEDs at the time were so inefficient. Heath used a 15 ohm current-limiting resistor for each segment to set the normal current at 10-15ma. But that would be something like 120ma if a segment stuck "on"! That would kill the LED.

I didn't think this was needed on the mini H8, as modern LEDs are so much more efficient. 1ma is plenty of brightness, and 10ma won't hurt them.

BTW: Yes, the human eye exaggerates the brightness of blinking objects like multiplexed LEDs. Photographic film is the opposite. I worked for Kodak and actually have a patent that makes use of this effect.

Glenn: I changed the key labels printed on the PCB slightly in an attempt to make them more mnemonic (STEP instead of SI, RESET instead of RST/0, MON instead of RTM/0 etc.) The keycaps can have the original names if that is preferable.

SI (or STEP) will be harder to implement without the H8's hardware single-step. It will only be able to step through RAM, by walking a RST7 instruction through the program like CP/M's DDT.

PS: Does anyone know how to make Gmail stop displaying the entire history in every post?

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On Wed, Jul 22, 2026 at 6:32 AM Douglas Miller <durga...@gmail.com> wrote:

I did realize/remember something regarding the display recently. The H8 Front Panel (which includes the 2mS clock) generates a "clear" on the segment refresh register at the end of the 2mS cycle, which effectively blanks the current digit at that time. This means that the software must update the digit/segment select registers "immediately" after the 2mS Clock interrupt signal, after which that digit will be displayed for about 1.5 mS. I think the main reason for this is so if (when) the software crashes - or interrupts get stuck disabled - that the display will go blank. Otherwise, the most-recently refreshed digit will be stuck on. I don't think there's any practical solution here for this hardware, but it's just some behavior to be aware of.

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[Douglas Miller]

The LEDs in the old FND500 are rated, per segment, at 20mA and able to sustain higher. They can handle 20mA easily continuously. I believe the clear circuitry was only to ensure the display blanked promptly when not being refreshed.

[Lee Hart]

Ah, but there are saturated transistors from VCC to anode, and cathode to GND, with only a 15 ohm resistor to limit the current. The average current while scanning is about 150ma / 9 = 16ma. But if the display isn't being scanned, then one digit gets the full 150ma per segment!

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[Douglas Miller]

The 15 ohm resistors are on the segment drivers, so I don't think you can exceed the recommended current per segment even if no scanning is going on. Only one digit can be enabled/driven at a time.

[Douglas Miller]

Oh, my math is off. The LED segment wants to drop 1.7V and so the 15 ohm would carry 3.3V and drive 220 mA. But, that seems too high, even for just 1.5 mS at a time. The schematic implies that the digit driver transistors drop 1V C-E which makes it more like 150mA but still too much. The FND500 data sheet specifies a max of 200mA for 100uS, but these pulses are 1500uS. If I had a front panel here, I'd measure with an oscilloscope and see what actually is happening.

[norberto.collado koyado.com]

I had a bad front panel in which the 74123 failed to turn off the LED’s when the CPU was not operational , and the LEDs got very hot. 

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From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Douglas Miller <durga...@gmail.com>

Sent: Wednesday, 22 July 2026 12:29:15
To: SEBHC <se...@googlegroups.com>

Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

To view this discussion visit https://groups.google.com/d/msgid/sebhc/50941e7e-1010-4518-985e-334195cc81b0n%40googlegroups.com.

[Darrell Pelan]

Hi Paul,

For what it's worth, Glenn and I used a Brother P-Touch PT-D610BT Label Maker to make labels. I 3D printed a jig to cut them with an Exatco knife. The jig is shown in my H8 video at 12:39. I also printed key caps for Terry Smedley's keyboard. Let me know if you want any more info.

  Darrell

[Lee Hart]

Thanks Darrell. Paul has printed some keycaps to fit the mini H8. They are 10mm square with a flat top, so H8-size labels would probably work! 

I have a Brother PT-D200. I experimented, and it won't let me mix font sizes on a label. The number and text had to be the same size, i.e. pretty small. Is your PT-610BD able to do that? Or did you have to make two labels, one with a big number and a second with smaller text?

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[ocl...@earthlink.net]

The P-Touch label design software, common to at least most of the Brother P-Touch label printers, don’t let you mix different fonts or font sizes in the same “text frame” within a label design. But the software DOES allow having more than one text frame within a label, and each frame can have its own font & font size. But doing that, one soon runs into issues with overlapping frames, unintended cropping, the less than precise and always irritating limitations with margins within a text frame, and the software’s tendency to spontaneously override your desires when it thinks some boundary, etc; has been violated. I have found the whole P-Touch product to be of immense help on so many projects, but for little/precise things like the H8 keycap labels, I have found that approach to be inadequate.

 

That is why I did not go that way with my efforts regarding the H8 Mini. Instead, I am using the free design software from Front Panel Express, which lets you do almost anything you want, and with great precision. But it requires LOTS of calculations to figure all the coordinates (it SUCKS at drag & drop positioning).

 

I have attached an image of where I am currently on the layout design. I have populated “placeholder” text at the three main positions in the first row of labels; this is just to allow me to adjust for closest appearance to my original H8 keypad. The software does not allow me to precisely mimic the original Heathkit font (but I think I have come pretty close).

 

Anyone wanting to use these will be able to get a PDF, which when printed on a laser printer (B&W or color) at 100% scaling should result in a very accurately sized set of labels. They are separated by bold white lines, making it easy to accurately cut them apart with a paper shear or pair of scissors, resulting in 9.5x9.5mm labels, just a hair smaller than the faces of my 3D printable keycaps.

 

They can be printed on paper, or on adhesive label sheets, etc. For my OWN H8 Mini, I will be printing to either 3M “Print To Last” paper or Xerox “Revolution Never Tear” paper; the two products are identical (I think 3M sold the product to Xerox a few years ago). This is a porous plastic ‘paper’ that is intended for making durable documents and labels using a laser printer (any xerographic printer/copier). The toner fuses into the surface structure and it will not come off, ideal for key labels. The material is impervious to liquids, sweat, oils, etc; and is dimensionally stable. The only downside is that it is not available with adhesive backing, so the user needs to apply the adhesive of their choice to either the keycap or the label and stick them together. I personally like the Scotch Extra Strength (permanent) “Tape Runner” for small labels, but many other adhesives will work well, including CA glue applied sparingly. One thing I can verify will NOT work is the Scotch Permanent Glue Stick product (it only works well on actual paper).

 

Paul

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Lee Hart
Sent: Friday, July 24, 2026 1:59 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

Thanks Darrell. Paul has printed some keycaps to fit the mini H8. They are 10mm square with a flat top, so H8-size labels would probably work! 

 

I have a Brother PT-D200. I experimented, and it won't let me mix font sizes on a label. The number and text had to be the same size, i.e. pretty small. Is your PT-610BD able to do that? Or did you have to make two labels, one with a big number and a second with smaller text?

 

 

 

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On Thu, Jul 23, 2026 at 8:45 AM Darrell Pelan <pel...@gmail.com> wrote:

Hi Paul,

 

For what it's worth, Glenn and I used a Brother P-Touch PT-D610BT Label Maker to make labels. I 3D printed a jig to cut them with an Exatco knife. The jig is shown in my H8 video at 12:39. I also printed key caps for Terry Smedley's keyboard. Let me know if you want any more info.

 

  Darrell

On Wednesday, July 22, 2026 at 12:14:15 AM UTC-4 Paul Schmidt wrote:

Hi Lee

 

I did a little bit of planning work on the H* keycaps. Had quite a headache for most of the last few days, so did not feel much like doing anything, but better today.

 

I have a few questions and observations on the subject of the keypad labels.

 

• I pulled out my H8 from storage, and indeed the labels measure somewhere between 0.4” and 0.41”; I suspect that the recessed keytops are actually right at 0.4”, as you said, and that the larger dimension is measurement error,
• That said, the keytops that I am designing will be smaller than 0.4” square. If they were exactly 0.4”, none of the keys would push, due to friction with other keys on 0.4” centers. So, any repro key labels that might turn up from somebody will require at least some trimming to fit the new 3D printed key caps, so no extra hardship for me to design my own laser-printable key cap label artwork, which would also need to be cut out. People making the kit, if they want to use key caps, could go either way on which labels to use.....EXCEPT some artwork on 0.4” square labels might be too close to the edges and thus might end up being cut off during trimming.
• I compared the PCB silkscreen legends with the label artwork on my H8. Some disparities I need your help with:

• S7 label says “SI” while the silkscreen says “STEP”.....the latter will fit, but I wonder if your version might do something else as noted by “SI”....?
• SP label says “REG”, but the silkscreen is blank in this regard......is this function not likely to make sense/be implemented?
• SM (?) label says “MEM” at the upper left and “RTM/0” at the lower right, but the silkscreen says only “MEM”......?
• SR label says “ALTER” at the upper left and “RST/0” at the lower right, but the silkscreen says only “ALTER”......?

• I am doing some experiments with different adhesives for the labels. I usually use Scotch Extra Strength adhesive roller/tape runner, which is truly strong and permanent. I am also trying Scotch Permanent Glue Stick, and CA glue. The glue stick has the advantage of being briefly repositionable during the first few seconds, but it is intended for paper and does not grip plastics nearly as well.

 

I hope to finish the 3D design and print the first experimental samples tomorrow.

 

Paul

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Lee Hart
Sent: Tuesday, July 21, 2026 4:37 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

The keys on the mini H8 are on 0.4" centers. Paul Schmidt is working on some 3D printed keycaps for it. I seem to recall that someone made replacement keycap stickers for the H8. They would be 0.4" square and could be used for the mini H8. Does anyone remember who made them?

 

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On Tue, Jul 21, 2026 at 3:48 PM Lee Hart <electr...@gmail.com> wrote:

Douglas, I think you're right. I forgot that the multiplexing will lower the total LED current, so it won't be as bad as my off-the-cuff estimate.

 

The high-state output resistance of the 82C55 is about 100 ohms. The LEDs have about a 1.8v forward drop. The 74LS145 has about a 0.5v drop. So the LED current is about 5v-1.8v-0.5v, so 2.7v / 100 ohms = 2.7ma. But only one digit is "on" at a time. Half the segments would be 2.7ma x 4 = 11ma.

 

When spread across 9 digits, I'm wondering if I may have a problem with not enough brightness.

 

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On Mon, Jul 20, 2026 at 11:30 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:

Done.

 

Thanks Lee!

 

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>
Date: Monday, July 20, 2026 at 6:51 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

Norberto (and Glenn): I'd be glad to send you a PCB, but I'm not sure I have your current address. Can you send it to me at <leea...@earthlink.net>?

 

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[ocl...@earthlink.net]

I have laid some of my new 3D printed H8 Mini keycaps face-down on the keypad labels on my old H8. With some VERY careful and tight trimming, it would just barely be possible to get the full-size labels to fit the new keycaps without actually losing any text.

 

I have attached the latest version (JPEG) of my own keycap label design, dimensioned optimally for the 10mm square faces of my new keycaps. I made the secondary text yellow, which I think looks better. But if printed as B&W, all text will appear white, so no separate B&W version is necessary. To those readers who saw my first version earlier yesterday, the only change here is that I increased the size of the secondary text slightly, which helps with clarity where certain letter combinations are closely adjacent.

 

Note that my design has the 16 labels in a 4x4 array, just like the keypad, and separated by 2mm-wide white lines. This will make it easier (than with tinner lines) to cut them apart. I recommend printing onto Xerox “Revolution Never Tear” laser-printable plastic paper. Choice of adhesive will be up to folks who choose to use my keycaps on their H8 Mini’s.

 

Once I get Lee Hart’s approval, I plan to put my 3D printer file, the PDF of these labels, etc; up on my fileshare webpage, and will make that URL known here.

 

Paul

 

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Lee Hart
Sent: Friday, July 24, 2026 1:59 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

Thanks Darrell. Paul has printed some keycaps to fit the mini H8. They are 10mm square with a flat top, so H8-size labels would probably work! 

 

I have a Brother PT-D200. I experimented, and it won't let me mix font sizes on a label. The number and text had to be the same size, i.e. pretty small. Is your PT-610BD able to do that? Or did you have to make two labels, one with a big number and a second with smaller text?

 

 

 

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On Thu, Jul 23, 2026 at 8:45 AM Darrell Pelan <pel...@gmail.com> wrote:

Hi Paul,

 

For what it's worth, Glenn and I used a Brother P-Touch PT-D610BT Label Maker to make labels. I 3D printed a jig to cut them with an Exatco knife. The jig is shown in my H8 video at 12:39. I also printed key caps for Terry Smedley's keyboard. Let me know if you want any more info.

 

  Darrell

On Wednesday, July 22, 2026 at 12:14:15 AM UTC-4 Paul Schmidt wrote:

Hi Lee

 

I did a little bit of planning work on the H* keycaps. Had quite a headache for most of the last few days, so did not feel much like doing anything, but better today.

 

I have a few questions and observations on the subject of the keypad labels.

 

• I pulled out my H8 from storage, and indeed the labels measure somewhere between 0.4” and 0.41”; I suspect that the recessed keytops are actually right at 0.4”, as you said, and that the larger dimension is measurement error,
• That said, the keytops that I am designing will be smaller than 0.4” square. If they were exactly 0.4”, none of the keys would push, due to friction with other keys on 0.4” centers. So, any repro key labels that might turn up from somebody will require at least some trimming to fit the new 3D printed key caps, so no extra hardship for me to design my own laser-printable key cap label artwork, which would also need to be cut out. People making the kit, if they want to use key caps, could go either way on which labels to use.....EXCEPT some artwork on 0.4” square labels might be too close to the edges and thus might end up being cut off during trimming.
• I compared the PCB silkscreen legends with the label artwork on my H8. Some disparities I need your help with:

• S7 label says “SI” while the silkscreen says “STEP”.....the latter will fit, but I wonder if your version might do something else as noted by “SI”....?
• SP label says “REG”, but the silkscreen is blank in this regard......is this function not likely to make sense/be implemented?
• SM (?) label says “MEM” at the upper left and “RTM/0” at the lower right, but the silkscreen says only “MEM”......?
• SR label says “ALTER” at the upper left and “RST/0” at the lower right, but the silkscreen says only “ALTER”......?

• I am doing some experiments with different adhesives for the labels. I usually use Scotch Extra Strength adhesive roller/tape runner, which is truly strong and permanent. I am also trying Scotch Permanent Glue Stick, and CA glue. The glue stick has the advantage of being briefly repositionable during the first few seconds, but it is intended for paper and does not grip plastics nearly as well.

 

I hope to finish the 3D design and print the first experimental samples tomorrow.

 

Paul

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Lee Hart
Sent: Tuesday, July 21, 2026 4:37 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

The keys on the mini H8 are on 0.4" centers. Paul Schmidt is working on some 3D printed keycaps for it. I seem to recall that someone made replacement keycap stickers for the H8. They would be 0.4" square and could be used for the mini H8. Does anyone remember who made them?

 

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On Tue, Jul 21, 2026 at 3:48 PM Lee Hart <electr...@gmail.com> wrote:

Douglas, I think you're right. I forgot that the multiplexing will lower the total LED current, so it won't be as bad as my off-the-cuff estimate.

 

The high-state output resistance of the 82C55 is about 100 ohms. The LEDs have about a 1.8v forward drop. The 74LS145 has about a 0.5v drop. So the LED current is about 5v-1.8v-0.5v, so 2.7v / 100 ohms = 2.7ma. But only one digit is "on" at a time. Half the segments would be 2.7ma x 4 = 11ma.

 

When spread across 9 digits, I'm wondering if I may have a problem with not enough brightness.

 

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On Mon, Jul 20, 2026 at 11:30 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:

Done.

 

Thanks Lee!

 

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>
Date: Monday, July 20, 2026 at 6:51 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

Norberto (and Glenn): I'd be glad to send you a PCB, but I'm not sure I have your current address. Can you send it to me at <leea...@earthlink.net>?

 

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To view this discussion visit https://groups.google.com/d/msgid/sebhc/CAF__8hewmzf7_E1DK__eN67Cbwp4bHg%3D4iGi%2BYvjGka4sCgYXw%40mail.gmail.com.

[Darrell Pelan]

Yes, the labels were a single print. When you use the label printer with your PC there is a lot of flexibility, including graphics.

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[ocl...@earthlink.net]

Darrell, that is a good point. Even though I use the Brother P-Touch stuff a LOT, I had forgotten about its ability to print graphics is using the PC software. It is still low-res, but it allows layouts that might not be possible in the software’s normal “text” mode. One can for example design the desired label in other software, save it as graphics file, and import it into the P-Touch software for printing.

 

Paul

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Darrell Pelan
Sent: Saturday, July 25, 2026 6:51 AM
To: se...@googlegroups.com
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

Yes, the labels were a single print. When you use the label printer with your PC there is a lot of flexibility, including graphics.

 

On Fri, Jul 24, 2026 at 2:59 PM Lee Hart <electr...@gmail.com> wrote:

Thanks Darrell. Paul has printed some keycaps to fit the mini H8. They are 10mm square with a flat top, so H8-size labels would probably work! 

 

I have a Brother PT-D200. I experimented, and it won't let me mix font sizes on a label. The number and text had to be the same size, i.e. pretty small. Is your PT-610BD able to do that? Or did you have to make two labels, one with a big number and a second with smaller text?

 

 

 

Virus-free.www.avast.com

 

On Thu, Jul 23, 2026 at 8:45 AM Darrell Pelan <pel...@gmail.com> wrote:

Hi Paul,

 

For what it's worth, Glenn and I used a Brother P-Touch PT-D610BT Label Maker to make labels. I 3D printed a jig to cut them with an Exatco knife. The jig is shown in my H8 video at 12:39. I also printed key caps for Terry Smedley's keyboard. Let me know if you want any more info.

 

  Darrell

On Wednesday, July 22, 2026 at 12:14:15 AM UTC-4 Paul Schmidt wrote:

Hi Lee

 

I did a little bit of planning work on the H* keycaps. Had quite a headache for most of the last few days, so did not feel much like doing anything, but better today.

 

I have a few questions and observations on the subject of the keypad labels.

 

• I pulled out my H8 from storage, and indeed the labels measure somewhere between 0.4” and 0.41”; I suspect that the recessed keytops are actually right at 0.4”, as you said, and that the larger dimension is measurement error,
• That said, the keytops that I am designing will be smaller than 0.4” square. If they were exactly 0.4”, none of the keys would push, due to friction with other keys on 0.4” centers. So, any repro key labels that might turn up from somebody will require at least some trimming to fit the new 3D printed key caps, so no extra hardship for me to design my own laser-printable key cap label artwork, which would also need to be cut out. People making the kit, if they want to use key caps, could go either way on which labels to use.....EXCEPT some artwork on 0.4” square labels might be too close to the edges and thus might end up being cut off during trimming.
• I compared the PCB silkscreen legends with the label artwork on my H8. Some disparities I need your help with:

• S7 label says “SI” while the silkscreen says “STEP”.....the latter will fit, but I wonder if your version might do something else as noted by “SI”....?
• SP label says “REG”, but the silkscreen is blank in this regard......is this function not likely to make sense/be implemented?
• SM (?) label says “MEM” at the upper left and “RTM/0” at the lower right, but the silkscreen says only “MEM”......?
• SR label says “ALTER” at the upper left and “RST/0” at the lower right, but the silkscreen says only “ALTER”......?

• I am doing some experiments with different adhesives for the labels. I usually use Scotch Extra Strength adhesive roller/tape runner, which is truly strong and permanent. I am also trying Scotch Permanent Glue Stick, and CA glue. The glue stick has the advantage of being briefly repositionable during the first few seconds, but it is intended for paper and does not grip plastics nearly as well.

 

I hope to finish the 3D design and print the first experimental samples tomorrow.

 

Paul

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Lee Hart
Sent: Tuesday, July 21, 2026 4:37 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

 

The keys on the mini H8 are on 0.4" centers. Paul Schmidt is working on some 3D printed keycaps for it. I seem to recall that someone made replacement keycap stickers for the H8. They would be 0.4" square and could be used for the mini H8. Does anyone remember who made them?

 

Virus-free.www.avast.com

 

On Tue, Jul 21, 2026 at 3:48 PM Lee Hart <electr...@gmail.com> wrote:

Douglas, I think you're right. I forgot that the multiplexing will lower the total LED current, so it won't be as bad as my off-the-cuff estimate.

 

The high-state output resistance of the 82C55 is about 100 ohms. The LEDs have about a 1.8v forward drop. The 74LS145 has about a 0.5v drop. So the LED current is about 5v-1.8v-0.5v, so 2.7v / 100 ohms = 2.7ma. But only one digit is "on" at a time. Half the segments would be 2.7ma x 4 = 11ma.

 

When spread across 9 digits, I'm wondering if I may have a problem with not enough brightness.

 

Virus-free.www.avast.com

 

On Mon, Jul 20, 2026 at 11:30 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:

Done.

 

Thanks Lee!

 

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Lee Hart <electr...@gmail.com>
Date: Monday, July 20, 2026 at 6:51 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Re: An H8 Badge for VCFMW

Norberto (and Glenn): I'd be glad to send you a PCB, but I'm not sure I have your current address. Can you send it to me at <leea...@earthlink.net>?

 

Virus-free.www.avast.com

To view this discussion visit https://groups.google.com/d/msgid/sebhc/CAKhgrKs%2BuNmEgcEvzs3ft1EfyVbcOaEQnoSRzcCaQaYcDp01Yw%40mail.gmail.com.