Sourcing a ZX81 ROM or replacement

[Moggy]

I referenced an EEPROM, as they can be programmed with an Arduino, and be erased the same way. I think the EPROM will require a special burner with different voltages, and erasing them requires UV light.

A 2764 which is the common one used for zeddies only requires two pins lifted and two wires soldered. It needs 21volts for programming which is usually outside the range of modern PC based programmers, the 27c64 as found on the early ZXpands requires only 12v.
Erasers can be picked up for a round a tenner from the land of the rising price, I've had mine about seven years and it does the job well.
The programmer I use was built at the time and can be powered by either the zeddy or in my case a ZX Spectrum.

If none of these things are available then perhaps contact Sell My Retro who I believe once offered a pre programmed device service though this may have changed.

https://www.sellmyretro.com/

[Orac]

I looked at programming an EEPROMas I thought that might be easier but the kit, not including the arduino Mega which I already have was as much as some of the eBay programmers. Bit much for a one time thing.

I know sellmyretro used to do rom’s but I can’t find the link anymore, things there seem to have gone downhill a lot recently after the European vat issues, etc. it’s obviously badly affected business and taken up a lot of time. I’m in the uk btw and looking for a ZX81 rom, ideally the bug fixed more common one, not the last one.

[mrtinb]

Writing an EEPROM with an Arduino is quite simple, and only requires 2 x 74HC595.

Ben Eater has schematic and Arduino source here: https://github.com/beneater/eeprom-programmer

M. Keller has a different design here: https://github.com/mkeller0815/MEEPROMMER

If you look at the schematics, you can see the idea is quite similar, but yet different.

That means that each design needs their dedicated software.

Ben Eater's design has the ROM hex values hardcoded in the Arduino source, and M. Keller's design is with a Java application, where binary files can be loaded and written to the EEPROM. The Java application needs a RXTX Java Native Library (JNI) for your operating system, to access the serial port hardware.

I have some spare PCBs for M. Keller's design.

[Orac]

Writing an EEPROM with an Arduino is quite simple, and only requires 2 x 74HC595.]

Actually that looks a lot better in terms of total components needed. So this is something I think I might explore just for fun anyway. Thank you.

[valentin]

I looked at programming an EEPROMas I thought that might be easier but the kit, not including the arduino Mega which I already have was as much as some of the eBay programmers. Bit much for a one time thing.
[...]

If you already have the Arduino Mega, you can build this simple EEPROM programmer. I purchased the PCB only for under £8 as I already had the other components. The ZIF socket is £2.79 on eBay and the other components (headers, resistors and LEDs) are pennies.

I built this programmer and it works quite well. I have successfuly written a 28C256 EEPROM.

I have no connection with the designer / seller other than being a happy customer.