Thursday, June 21, 2012

Breadboard Z80 computer under-clocked to 6.8 Hz

Yes, you heard right, not MHz, not kHz... but Hz. Yeah, and I bet trying to get actual work done on such a contraption just plain hurts too. ;) Sorry.


I was pretty floored to find this simple NOP tester circuit at Slight change to the circuit, I used a 555 in an Astable mode for the clock source. By changing capacitors I can run at either 6.8 Hz, or a crazy-fast 68 Hz.

I've been on quite the inexplicable retro-computing kick, likely from the NSL Assembly Language class. Its bringing back memories of the Z80 asm class I took at Mt. Sac long ago, and before that, of the weird PC-looking device I bought at a government warehouse back at the dawn of the Internet age when I was in College. I had hoped my $7 was buying a PC that I could get on the (test-based) Internet with, instead my nerdy dorm-neighbors informed me that it was some sort of gubmint data terminal, and even though it looked sorta like a PC, there was no way in hell it'd run MS-DOS, due to the Zilog Z80 CPU it had.

Going waaay farther back in time... In 5th grade we got to play with the Commodore PETS at school, and later that year I got my own C=64 for my birthday. Oh, how rich I'd be today if I would have only learned machine language back then! ;) Sure...

Anyway, I had always thought building a computer from discrete components, though a total waste of time from a practical standpoint today, would still be cool as hell.

The other day I found this site, The guy sells blank boards for his single board computer for $20, and I likely have all of the other pieces in my junk box, so I think I'll order one.

And yes, I have seen , I'm trying to justify the expense. ;)

I do want to cobble a dumb terminal together with a pair of Arduinos and and old trash-day CRT TV, to re-create the carppy video experience of those old Commodore 64 days. Maybe even snip the driver wires to the Blue and Red guns so I get that awesome Green-a-chrome screen.Would be the perfect thing to use with the Z80 single board computer. Or, I could use my Teletype, hmm... ;)

Video of the NOP tester running. The video clearly shows a wiring error I made... Its in the still picture above, too, can you find it?

Tuesday, June 5, 2012

Venus Transit, 6/5/12

I only set my telescope on fire a little bit. ;)

Look, sunspots!

Venus transit, 6/5/12