Re: 20/20
I added an external keyboard (adapted from a Tandy keyboard by repainting the conductive tracks on the flexible membrane and keyboard legends cut out from a magazine picture stuck on to the top of the keys with clear tape), together with a power switch on the keyboard. The ZX81 then sat untouched on a shelf, well away from poking fingers.
Once there and safe from unwanted movement, I added a Quicksilver expansion board and sound card, together with an additional modulator to add the sound to the TV signal. I also hacked around with the internal 1K of memory, mapping it into a different address in the memory when the RAM pack was installed so it could be used, and also added a second 1K of static memory on the ULA/ROM side of the bus isolation resistors which allowed me to use it as a programmable character map by manipulating the I register that was used to hold the page address of the base of the character table.
I never had any problems with it until my (homebrew) power supply popped it's bridge rectifier and fried the rampack!
Good memories.
Biting the hand that feeds IT
