Converter/adapter to hook up conventional PC keyboard to H19/H88/H89?

[Bob Groh]

While working on my H-89s 'back in the day' (and again with the two I now presently own), I remember a strong desire to replace my H-89 keyboards with a conventional PC based keyboard - preferably with a 'converter/adapter' between the PC keyboard and my H-89 (both for a better feeling key action and to have a remote keyboard.

Does anyone have a links or ideas to throw my way?

Bob Groh

(Heathkit engineering, 1977 to 1981)

[Joseph Travis]

I'm unaware of anything currently out there that does that.  I think most would attempt to interface another keyboard to the TLB using the existing interface with a microcontroller; however another possibility would be to utilize the serial connection between the TLB and CPU boards.  That method would allow the existing keyboard and/or the external keyboard to be used.

Joe

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[Steven Feinsmith]

Utilizing an IBM-compatible keyboard and devising an interface for the H-8x series presents challenges due to the disparate keycaps on the top row. I advocate the development of a new PCB integrated with reliable Cherry MX switches to supplant the original ones. The keycaps can be meticulously customized to replicate their original counterparts. A pivotal task involves creating a microcontroller to supplant the original one and establish compatibility with the H-8x series. It has come to my attention that the original keyboard encoder, referenced as MM5740, exhibited heightened susceptibility to static electricity and was susceptible to damage or no longer function due to aging. Regrettably, this chip is presently obsolete. The updated PCB iteration would facilitate seamless keyboard replacement without modifying the remaining circuitry. I have had the privilege of owning the H19, H88, H89, and H110 keyboards, all of which have been functioning impeccably as of late. However, it is essential to acknowledge that their longevity is not indefinite.

Steven

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[Lee Hart]

The stock MM5740 is indeed quite susceptible to static electricity. I confirmed this the hard way when I added a longer keyboard cable so the stock keyboard could be extended and used in my lap.

But in the stock configuration, it's pretty unlikely to be able the "zap" its inputs. The danger occurs when handling the chip out of its socket, or touching the keyboard cable inputs when the keyboard is unplugged. This is a place where antistatic practices are important!

Replacing the keyboard and MM5740 is quite a project; but possible. One thing that helps: There is a 2716 2k ROM between the MM5740 and the bus. It functions as a key row/column to ASCII converter. Your PS2-to-H19 adapter could just create the 8-bit ASCII codes produced by this ROM (plus the shift and control keys that are not routed through it). A PS2-to-ASCII parallel adapter may well have already been designed by somebody.

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[Steven Feinsmith]

I found an application sheet for the MM5740 keyboard encoder. It is possible to use an FPGA to create an MM5740 emulator, but I have no programming skills. Perhaps anyone has the skill to create the FPGA into an MM5740 to run the Heathkit H-x series.

https://telcontar.net/KBK/National_Semiconductor/docs/National%20Semiconductor%20application%20note%20AN-80.pdf

Someone capable of doing that project will significantly benefit the H-x series.

Thank you,

Steven

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[Lee Hart]

It will be a real challenge to build a replacement without programming. The PS2 keyboard format basically *requires* a micro to read its special serial output format. Newer PC keyboards with USB or other interfaces are even harder. You may have to find someone that has already built and programmed a PC keyboard to ASCII converter for you.

On the other hand, replacing the MM5740 with a non-programmed circuit is fairly straightforward. See Don Lancaster's classic "CMOS Cookbook" for one example (figs 3-34 and 7-18).

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[Joseph Travis]

This could be a good candidate for a Rasberry Pi project...

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[geneb]

On Fri, 17 May 2024, Joseph Travis wrote:

> This could be a good candidate for a Rasberry Pi project...
>

A Pi Pico maybe. A full-on Pi would be WAY overkill. :)

g.

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[Lee Hart]

A microcontroller to replace the MM5470 is going to need at least 36 I/O pins.

But if you're replacing it with a PS2 or USB PC keyboard interface, the pin count is a lot more reasonable.

The "horsepower" needed to do the job is trivial. But everyone loves over-complicated solutions; so a Pi is peachy keen! :-)

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[Terry Smedley]

I think the pieces to do this exist for use without any further development work.

The H89 console can be easily piggybacked to another serial device using "auctioneer diodes".  Chris Elmquest published such a circuit a while ago (see the attached PDF).

The hardware and firmware to generate serial H19 ASCII codes from a USB keyboard are included in the Propeller "H19 Serial to VGA" project described here: https://groups.google.com/g/sebhc/c/o_ECreoLUtQ/m/61sQfzObGQAJ (Search "H19 in a Box").  You don't need any of the VGA circuitry from that project - that circuit and firmware can be used to do only the keyboard translation.   That box uses the FTDI Vinculum II V2DIP1 module to handle the USB interface.  The V2DIP is fully USB HID compliant, so it works with any similarly-compliant PC keyboard.  You can, for example, use a Logitech Unifying dongle to support a wireless connection to a Logitech keyboard.

Can't argue that there are simpler processors that could be used to do the PC scan code translation, but this solution doesn't cost much, and the firmware and PCBs have already been developed.

Here's an example of a PC USB keyboard with custom-printed keycaps for the H19 functions.  

I don't have an H89 to proof this, but I'd be happy to send an assembled "keyboard only" PCB to someone willing to connect it to their H89 using Chris Elmquest's piggyback circuit and report their results.

tas

[Peter Higgins]

Here is a PS/2 keyboard adapter with ASCII output via both a parallel and RS232 serial output:

https://store.go4retro.com/ps-2-keyboard-encoder/

[Glenn Roberts]

Ah. So Elmquist’s auctioneer diodes let this coexist in parallel with the original keyboard? Clever. I’m happy to give this a try, but also happy to let Bob or someone else run with the ball…

Sent from my iPad

On May 17, 2024, at 9:22 PM, Peter Higgins <higgin...@gmail.com> wrote:

Here is a PS/2 keyboard adapter with ASCII output via both a parallel and RS232 serial output:

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[dwight]

This is likely not exactly what you are looking for. On:

https://github.com/prog4004/Blue-EForth

you'll find some programs that I fiddled with using a "Blue Pill" These are like an Arquino but a lot cheaper ( under $5 each ).

I do not use the Arduino loader ( that you can use to load nice C programs with). My code is based on  EForth and I use the manufactures method to program it with EForth and the AT to parallel decoding.

Unlike the one shown on the picture, you only need some 9 each 10K pullup resistors, some wire, the connectors to the keyboard and whatever the H89 uses. It is a parallel output that with a strobe. I don't recall if the H89 uses such but it seems I recall the H89 scans the keyboard so it would take some additional programming, as the code I have reads the AT keyboard and generates the parallel out with a strobe to tell the computer there is a key waiting.

To program the Blue Pill, you'd need a RS232, 5V drive ( not typical RS232 +/- voltages )

I've written my own programming code, that I think runs on FPC Forth to a serial port.

Since I don't use the Arduino interface, I don't waste space on the Blue Pill to have a loader but it does have a nice Forth to do experiments on the Blue Pill. The Forth has a typical Forth interpreter/compiler that only needs a RS232 communication to make programs on and it has code to make the application code self booting in the flash memory.

If you prefer to use C and the Arduino IDE you still need the 5V RS232 interface to download the Arduino loader code.

The STM32F103 has the advantage that there are a number of 5V I/O that only need the pullup resistors to drive typical 5V logic on one of the ports.

Dwight

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From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Peter Higgins <higgin...@gmail.com>
Sent: Friday, May 17, 2024 6:22 PM
To: SEBHC <se...@googlegroups.com>
Subject: [sebhc] Re: Converter/adapter to hook up conventional PC keyboard to H19/H88/H89?

 

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