Found this interesting use of a ZX81 on twitter

[blackdalek]

A ZX81 controlled radio linked Dalek...

https://twitter.com/Toymaker2/statuses/889860628004966401
https://twitter.com/Toymaker2/status/893133861030432768

[Gryzor]

That'd have been the most harmless Dalek ever. Climbing stairs? Pah!

[Bryce]

Best use for a ZX81.

Bryce.

[Gryzor]

True story - for some time I used one to prop up some binders at my office because they would keep sliding downwards. Its slope fitted perfectly, and also saved everyone from the temptation of 'typing' on that keyboard.

[VincentGR]

I like this machine, I have a timex 1000 with expansion ram and hi-res mod.
The problem is the keyboard, you can't play games with this shit.

[tjohnson]

Best use for a ZX81.

Bryce.

Lol, was this the computer that had something like 4kb of memory?

Sent from my E5823 using Tapatalk

[Bryce]

Only if you owned 4 of them. It came delivered with a whoping 1kb of RAM, but could handle up to 16kb. The keyboard is a wreck and it only does black and white.

I have one here, but I haven't switched it on in years.

Bryce.

[tjohnson]

I knew it didn't have much memory as my mate justin who now works as an engineer for the bbc said he had one as his first computer.  I never saw one myself,  a school friend had a zx spectrum with the rubber keyboard, that was my only real experience of a sinclair machine.  I remember playing skool daze on it and wishing i could get it for the amstrad.

Only if you owned 4 of them. It came delivered with a whoping 1kb of RAM, but could handle up to 16kb. The keyboard is a wreck and it only does black and white.

I have one here, but I haven't switched it on in years.

Bryce.

Sent from my E5823 using Tapatalk

[VincentGR]

Actually the Timex (ZX-81 U.S model) has 2KB 

[ThomH]

It's actually a pretty interesting machine, at least in terms of video generation. It uses the Z80's program counter as an address counter for video fetching*, the I register as a base address for its character set** and the refresh counter to keep track of horizontal position***.

* the Z80 thinks it is executing the display area. Except that the video circuits are stealing whatever is actually on the bus and forcing all lines to 0 before they get to the Z80. So it's actually just performing NOPs, at sequential addresses.

** video fetch actually happens in the refresh cycle that follows each matching instruction fetch and replaces only the low part of the refresh address, which from the Z80 uses I as the high part.

*** during applicable refresh, bit 5 of the refresh address is fed back to the Z80 as the interrupt input. So the refresh address is used to break the Z80 out of the video memory-reading NOP cycle as soon as it reaches 32.

EDIT: regarding the 1kb RAM, the scheme above is really helpful. Lines of text needn't be the full 32 characters in length. Just chuck a HALT in there and the part that forces a NOP will let it through. So your storage for an empty line is just one byte. Indeed for any line less than the full 32 characters long it's (number of visible characters from the left + 1). If they hadn't done that, you'd always have to spend a full 768 bytes on the display.

As soon as you have more than 1kb, it just uses an ordinary 32 byte by 24 line buffer, as the manipulations are faster.

[Bryce]

If anyone wants to explore the "power" of this machine, let me know. I have one that's looking for a new home.

Bryce.

[EgoTrip]

Best use for a ZX81.

Bryce.

You have to admire the foresight of Clive, he certainly knew the strengths of his machines and designed the cases accordingly.

[Gryzor]

Actually the Timex (ZX-81 U.S model) has 2KB 

Those Americans and their size insecurities...