Buying a Gigatron
At PyCon UK 2022, Peter Russell gave a talk on the Gigatron "a minimalistic retro computer" that you make yourself. By the end of Peter's talk, I'd found an eBay listing for a Gigatron printed circuit board (PCB). A few minutes after the talk, I'd bought the PCB.
Considering how little I know about computer architecture or electronics, not to mention the very little soldering experience, it wasn't the wisest decision I've ever made. But after getting home from PyCon, I figured I might as well follow through and started working out how to buy the other parts.
The inventors of the Gigatron, Marcel van Kervinck and Walter Belgers, used to sell Gigatron kits. These days it's a DIY affair. (A few companies do sell Gigatron kits but not in the UK. The kit prices are high enough that they seem likely to fall foul of import duty, VAT and the associated delivery fees.)
Luckily the Gigatron website has a detailed assembly guide and a bill of materials. Even more usefully, the bill of materials has links to the components on various electronics websites, including Mouser, DigiKey and Farnell. Mouser seemed to have the best reviews and promised to handle things like UK VAT, avoiding nasty delivery fee surprises, so I went with them.
Putting together a basket of 37 components veered wildly between straightforward and confusing. Some items had lead times of a year or more and I wasn't patient enough to wait that long. The ERPOM (erasable programmable read-only memory), the microcontroller for the PS/2 keyboard adapter, zener diodes, and several of the simpler chips seemed to be in very short supply.
Swapping out parts meant a lot of Googling, trying to work out the difference between a CD74HCT244E, a SN74HCT244NE4 and a SN74HCT244N. The most important part seemed to generally be in the middle, e.g. 74HCT244, with other letters being manufacturer codes.
Nearly all the chips in the Gigatron are 74HCT, which I learned is a specific "logic family". The most important thing for me was that chips with that code are compatible with each other, for example they expect the same power supply. There are closely related chips, like the 74HC or 74LS, that seem to be compatible if you fiddle a bit with the circuit. I was absolutely not going to do that and stuck to the 74HCT chips.
For the items with long lead times, like the EPROM and the ATtiny85 microcontroller, I went to eBay. eBay had the components, or seemingly compatible ones, but the listings seemed expensive. (Surely a 1MB EPROM didn't cost £6 before the electronics shortage happened??) But in for a penny, in for a pound. (Too many pounds...) The information in the Gigatron bill of materials was fantastic again and I managed to find components. Hopefully I got something workable.
There are still a few things on the shopping list, not least the famicom-style controller and a box to hold the Gigatron. But with small and large parcels falling through my post box most days, ordering those can wait a while.