ZX81 (7)
Retro Challenge 2024/10 - Schrödinger's PCB
The ZX81 Module I designed in 2016 has been an example of Schrödinger's PCB. It has sat around for 8 years in both a state…
Retro Challenge 2024/10 - Defeating The Riddler
The schematic for the ZX81 Module I designed in2016 had been designed in a very old version of KiCad, and hadn't survived all the upgrades…
Retro Challenge 2024/10 - Finding a donor
If you remember from my initial post at the start of the month, the first thing that I needed to do in order to make…
Retro Challenge 2024/10 Update 1 - The Riddler
When I failed to complete the Retro Challenge in 2016 I finished by saying that the dog ate my homework. That sounded like a reasonable…
Retro Challenge 2024/10 - Intro Post
It has been a while since I entered Retro Challenge, but I think I remember what to do. It goes something along the lines of…
Retro Challenge 10/2016 - Still a work in progress
So, who remembers my entry for Retro Challenge in January? It was quite devoid of effort and results I think you'll agree. Well, this time…
Retro Challenge 2016 - My Dog Ate My Homework
So, all the way back in deepest darkest December, I announced I would enter the Retro Challenge 2016 competition that ran throughout January. Those of you that followed by blog or Twitter account when I did this in 2014 will know that I blogged and Tweeted relentlessly for the whole month, but, this time around, almost nothing. Obviously, I'm keeping some secret about an amazing breakthrough or something, right? Well, truth is, I've done almost nothing.
Things started well, and on 1st January, I designed a new backplane for the RC2014. Although I hadn't studied the circuit diagrams for the ZX81, Jupiter Ace or ZX Spectrum yet, I knew that there were resistiors between the Z80 CPU and other devices. The stripboard backplane I'd been using had served me well, but it was time to progress to a better solution, and one that could be adapted better to my needs. Knowing that PCB delivery times could be against me, I thought it best to crack on and get this ordered.
The basic circuit is very very simple - however, I wanted to get this just right, not only for Retro Challenge 2016, but for other possible RC2014 uses. Essentially, there are 8 40 way connectors that are linked straight through - however, the data lines and address lines for the leftmost 2 connectors and rightmost 2 connectors are separated by a pair of pads. These can either be shorted together for up to 8 commoned connectors, or have resistors soldered across them. I also added a power connector and the option of either running 5v directly in to the board, or regulating a higher voltage down via a LM7805.
