Militarised ZX81

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
sirmorris
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Militarised ZX81

Post by sirmorris » Thu Aug 30, 2012 10:44 pm

This machine is being prepared for the rigours of live performance. When complete it's heading to Poland to hopefully take a place on stage with Yerzmyey and the AY Riders.

The zxpand has a pin header where the edge connector would normally be. This mates with a precision socket connector soldered to the zx81's edge connector. The machine itself is bolted to a plate of 1/8th inch plexiglas, and the plate will have a neoprene non-slip surface applied. There is a PCB guide there which will prevent any further movement of the zxpand. The AY boards will also have these. Oh did I mention it'll be a twin AY board? 8-)

The video conditioner is courtesy of our very own Pokemon, and I'm looking at a cool regulator option.

Power entry will most likely be available via a locking barrel connector at the rear.

I'm looking at options to fix the machine's lid at the moment - hence the questions about shortening membrane tails earlier.
milspec.JPG
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Last edited by sirmorris on Fri Aug 31, 2012 10:29 am, edited 1 time in total.

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Andy Rea
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Re: Militarised ZX81

Post by Andy Rea » Fri Aug 31, 2012 12:38 am

nice ;)

Will this be an upgrade option for All ZXpand users :?:
6 x ZX81, 1 x TS1500 , 1 x +3e, 1 x timex 2040 printer, 1 x timex 2020 cassette deck, siclair printer and some spectrum

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Paul
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Re: Militarised ZX81

Post by Paul » Fri Aug 31, 2012 7:19 am

Wow, the ULA has a date code 8119, so on the bottom side there will the printing 2c158?
Did this Zeddy have any mods? Which version is the ROM? The very early or was is it replaced since then?

If this is beeing used on stage, I would advise to have the ULA conserved and replaced against a AndyRea type to prevent overheating troubles.
12:23 ARRG I just saw this Zeddy comes from the small period where the old ULA was soldered in :evil: before Sinclair was aware there were problems with the ULA :(
I haven't seen this often on issue one boards.
Last edited by Paul on Fri Aug 31, 2012 12:26 pm, edited 1 time in total.
In theory, there is no difference between theory and practice. But, in practice, there is.

sirmorris
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Re: Militarised ZX81

Post by sirmorris » Fri Aug 31, 2012 10:40 am

Good spot, Paul!

<And say Hi from me to your family!>

XorA
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Re: Militarised ZX81

Post by XorA » Fri Aug 31, 2012 2:15 pm

Paul wrote:Wow, the ULA has a date code 8119, so on the bottom side there will the printing 2c158?
Did this Zeddy have any mods? Which version is the ROM? The very early or was is it replaced since then?
Is there something special about this ULA? I might have one but Im currently travelling so I cannot check.

sirmorris
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Re: Militarised ZX81

Post by sirmorris » Fri Aug 31, 2012 2:46 pm

I can't remember where this board came from; I think it was one which arrived in a job-lot. All I know about it is that this is how it appeared :)

C

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Paul
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Re: Militarised ZX81

Post by Paul » Fri Aug 31, 2012 3:04 pm

XorA wrote:Is there something special about this ULA? I might have one but Im currently travelling so I cannot check.
I have not yet found any documentation about the 2c158 ULA
I own one with date code 8127. That is nine weeks later than the one from SirMorris.
I would like to find more infos about this "unknow" ULA. E.g. Differences to the 2c184.
And if any mods were neccessary to get this working. And why a new one was made. There must be an error inside. Otherwise Sinclair would not have made a 2c184.
In theory, there is no difference between theory and practice. But, in practice, there is.

XorA
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Re: Militarised ZX81

Post by XorA » Fri Aug 31, 2012 3:10 pm

I shall try and remember to check if one of my machines has this when I get home next week. I shall if I do take hires pictures for you.

G

sirmorris
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Re: Militarised ZX81

Post by sirmorris » Fri Aug 31, 2012 3:16 pm

I guess the only way to know for sure is to get them de-capped and examined under a microscope:)

C

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RetroTechie
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Re: Militarised ZX81

Post by RetroTechie » Fri Aug 31, 2012 6:45 pm

A circuit board sticking out vertically isn't rugged in any way, shape or manner... Put the whole into a bigger case that's safe to bump into. Perhaps a suitcase / toolbox style case, where you can open the top to access the keyboard, but leave it closed when you use other controls (joystick etc). Plexiglass would be cool, but make ventilation holes in that case. Make sure that a pull on ANY cable doesn't rip a connector from the circuit board, but causes a pull on the case only.

Also I suggest reverse polarity protection (for example a 1A smd Schottky diode) in series with the unregulated DC input. Plus a power LED, so that it's easy to see when the machine is powered, before someone rips out ZXpand or an AY board by accident. If peripherals don't need it, consider cutting the track from unregulated DC to edge connector, to limit damage when cards are pulled / inserted with the machine powered.

Unless those AY boards have good power supply filtering, a linear regulator (7805) might be preferred for sound quality reasons alone. If this machine sits inside a bigger box: use a metal one, and screw 7805 to that (perhaps electrically isolated). Another option: cooling plate that's 2-3 times longer (or is that: wider?) than original one. Consider adding a few extra 100 nF decoupling capacitors here & there on the board - electrically speaking, a musician's stage might be a very noisy environment.

And yes I'd go for a replacement ULA too. And new SRAM (to keep it simple: 16K mod?). And perhaps CMOS Z80 + freshly burned EPROM instead of 30 years old ROM.

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