ZX81 Nixie Clock

[Michel]

After cleaning out the garage a few weeks ago and stumbling across my
good old ZX81 (well, TS1000 really), I thought it would be quite
interesting to turn it into a Nixie Clock!

Here's the result:
http://xiac.com/Images/ZX81NIXIECLOCK.jpg

I designed it with TTL logic, no SMD components here. It is direct
drive using 4 K155ID4 drivers.

If there is enough interest, I will offer this clock as a kit.

Michel

[Quixotic Nixotic]

Sir Clive Sinclair is very cranky these days. He lives on the south side of Trafalgar Square in central London and depending on his mood you never know whether he's going to get bored and fall asleep, throw you out or take you to his favo(u)rite lap dancing club.

He's an enigma, for sure. He gets a bee in his bonnet about something and finds it hard to take any constructive criticism. A flawed genius.

John S

[Michel]

Seems like you personally know him? :-)

I actually made this clock so that my wife wouldn't mind a ZX81
standing in the living room :-). If it wasn't a clock, it would have
ended up in the bin I guess.

The design was pretty straight forward of course but the real
difficulty was to make it an accurate clock. The ZX81 frame interrupts
(50Hz or 60Hz) don't come at exactly 20ms or 16.67ms intervals, in
fact, without calibration routines the clock will run about 7 seconds
fast every 10 minutes!! I made some calibration algorithm that could
do additive calibration. Suppose you start with "roughly" 7 seconds
per 10 minutes (skipping about 1 tick every 85 ticks @ 50Hz), then
after say 2 hours you measured the clock runs 3 seconds slow, so you
add to the previous calibration a 3/7200 correction. Then you take a
measurement over 24hours and say it now runs 2 seconds fast, so you
add a correction of -2/86400. If you do this, you eventually end up
with a routine that can skip a tick every say 91.13579 ticks and it
will (in theory) run as accurate as 1.5sec/year. Of course, not
including effects of ambient temperature.

I was surprised to see how active people still are with the ZX81/
TS1000, I haven't used mine for like 25 years or so. They cost peanuts
on ebay. This kit is about AU$175 so including the ZX81 it is less
than $225.

Michel

[J Forbes]

Looks good! Old computers are fun, they still do what they used to do when they cost a lot, but now they're cheap and we can discuss them on the internet....

 I cheated on my vintage computer nixie clock....I used one of David's old kits, and just stuck it into an early IBM case (which also houses our media computer, so it gets to be front center in the living room)

http://selectric.org/ibmpc/atxpc33.jpg

[Quixotic Nixotic]

On 22 Apr 2013, at 12:31, Michel wrote:

> Seems like you personally know him? :-)

He's a close friend of my inventor brother in law who took me along to meet Clive Sinclair last year. We didn't do the strip club and fortunately he wasn't grumpy that day either.

John S

[Michel van der Meij]

Thanks Jim, that's a great looking IBM you got there!

No cheating on the ZX81 clock though. I posted the schematics to a dedicated facebook page:

https://www.facebook.com/Zx81NixieClock

It is really not much more than an address decoder and some latches :-).

The hours and minutes are written to the latches with a simple instruction OUT (C), A with the hours in B and minutes in A (both in BCD of course).
Every time the latches are written, the state of the colon lights is inverted. So writing the latches twice per second keeps the colon flashing. The HV power down is active when $0C is written to the minute register. You would need to write this twice, I did that because I didn't want the HV circuit to turn on in the case power was restored after a power failure.

Michel

[Wayne de Geere]

OMG where did you get the old XT enclosure? I finally threw mine out in 2010, it had been in the garage since I got it in the early - mid 1980s.

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[Oscilloclock]

Michel, that is beautiful! I love it!

Being in Oz you may also know the Dick Smith CAT computer, an Apple II clone also known as the Laser 3000. Several years back I designed a 'graphics card' to interface my CAT to a modern *SVGA LCD screen.

Now you give me an idea - interface it to my Oscilloclock!!

Aaron
http://oscilloclock.com

[Michel]

Thanks Aaron,

I've only been in OZ for about 10 years so I know Dick Smith but not
his Apple II clone :-)

Yes, the possibilities of retro clocks is basically endless. The ZX81
only has 1k RAM including the screen memory and system variables... It
is actually pretty hard to write some clock software in so little
memory! I can finally set the time (had not yet implemented that). I
think I got about 10 bytes free or so, not a lot :-). Anyway, this has
been a fun project writing some code for the good old Z80! I remember
in the 80's I wrote the assembler down on sheets of paper, then
converted it to machine language through a look up table in the
manual, then had to type all these numbers into a REM statement. It's
a bit easier now having a decent editor and assembler!

Another funny idea would be to take a matrix of INS-1 tubes (say 64x48
or so) and then make a pong game for an Apple II :-)

Michel

[threeneurons]

That's a beauty ! I've got an old Sinclair ZX80 stashed away. Its the white bodied one that, I think, precedes this one. I'll have to dig it out, and see what I can do with it.

[Michel van der Meij]

It's a bit more difficult to turn a ZX80 into a nixie clock as it doesn't have a NMI circuit (you can add that by using a ZX80 to ZX81 conversion). The NMI is used to build up the screen in SLOW mode (ZX80 doesn't have SLOW mode) and this interrupt vector can be re-directed to your own interrupt routine to run a clock routine.

Alternatively, you can generate a 2Hz NMI with external parts but you would have to patch the ROM as there is probably no NMI interrupt vector set.

You can find all the details here:
http://searle.hostei.com/grant/zx80/zx80nmi.html

Michel

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[Michel]

Uploaded a video to youtube:
http://youtu.be/WbNsSN-XIdg

I added some cathode poisoning prevention to it, couldn't do much more
than just revolving the digits as there's no more RAM left :-)

The INS-1 colon tubes are now lighting up in the back of the tube
rather than the front. Anyone knows why is that? I think I connected
them the right way, the glass envelope has a small dot at one of the
leads which I am pretty sure is the cathode. I drive them just over
0.5mA which is slightly too much, but that shouldn't reduce their
life span to just a couple of days, right?

Michel

[Michel]

The open source code is now available for download:
http://xiac.com/ZX81/ZX81NixieClock.zip

Further instructions on how to use it can be found on the Sinclair ZX
World forum:
http://www.sinclairzxworld.com/viewtopic.php?f=6&t=1127

Michel

[Dan Harboe Burer]

Hello Michel,

If you make a kit (or a batch of PCBs , then I am interested :)
I just stumbled over - and bought - a ZX81 with Printer and 32K memory
expansion at a local Ham market !

Regards
Dan


-----Oprindelig meddelelse-----
From: Michel
Sent: Saturday, April 27, 2013 8:11 AM
To: neonixie-l
Subject: [neonixie-l] Re: ZX81 Nixie Clock

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[Michel van der Meij]

Hello Dan,

That's a nice buy! Is it a real ZX81 or a TS1000? I would advice you to put a heatsink on the ULA and replace the 7805 with a switched mode regulator. Especially if you want to run it 24/7 as a nixie clock as the ULA's get uncomfortably hot (a known problem of the ZX81/TS1000). The heatsink and SMPS will for sure extend the life span. If you have a TS1000, it is very simple to replace the 7805 and re-use its original heatsink for the ULA. I glued it to the ULA with some silver epoxy.

 

I don't have a complete kit but I can sell you the PCB. I got some extra tubes and K155ID1 drivers so you can either buy the PCB only or with the tubes & drivers. I got to see how much I actually paid for these items but I guess the board was around $25 and the tubes + driver about $6. So the whole set would be around $55 including 1 spare tube & driver ex postage. There are a few mods that need to be made to the board as I had put the tubes up-side-down (.....). This is a relatively easy mod though as most is done in the software, so it ended up only having to re-route 2 pins of the IN12 tubes.

 

If you have troubles connecting your ZX81 to an LCD TV, I got a simple mod here on the facebook page:

https://www.facebook.com/Zx81NixieClock?ref=hl

 

This mod only works for 210 type ULAs, other ULAs require a special circuit:

http://www.sellmyretro.com/offer/details/Sinclair-ZX81-ZXVid---Composite-Video~~ULA-Fix-%28self-fit%29-2338

 

Join the SinclairZxWorld forum, there's lots of information available. The software was writtent in PokeMon's ZX-IDE which is a fantastic tool for ZX81 assembly programming.

 

OK, have fun!

Best regards,

Michel

 

 

 

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[Michel van der Meij]

Oh heck, why do these emails reply default to neonixie-I ???

Sorry Dan, anyway, there was nothing secret going on here :-)

 

Michel