EPROM Emulator is a tool that can temporarily replace an EPROM memory chip inside your "target" device. You can plug it into your computer and "upload" a new version of code in seconds

Imagine you are developing software (well, firmware more likely) and you need to change the “program” in your EPROM memory. That means, remove the EPROM from its host computer, subject it to 20-30min of UV light exposure, program it with EPROM programmer, and re-install it on the host computer. The entire process is extremely slow and has to be repeated every time you want to make even a tiny one-bit change! And yes, there are modern EPROM alternatives based on Flash technology, that could save you the 20-30 min erase time, but the rest of the process is still the same and still annoyingly slow if you’re writing code and trying to “debug” it. This is where the EPROM emulator comes in handy, a device that can temporarily “replace” your EPROM chip, it is controlled by a computer and can be reprogrammed in seconds. Once you finish testing you can replace the emulator with an EPROM chip programmed with the final version of your code.

It's perfect for developing code for older 8-bit computers, Z80 "monitor" development etc. I even use it as a "universal" cartridge for my commodore 64.

Links to the BOM from Digikey are posted on my GitHub, you can swap the hard-to-get 25LC512 EEPROM with CAT25512VI or M95512 but since those are only available in SMT you will need a SOP8-DIP8 adapter - all those are included in the Digikey BOM)

Update (July 10 2022): uploaded new Gerbers for hardware version 2.2d (added support for the cheaper and easier to get DIP28 probe TLY 3100-28P)

Update (Apr 10 2021): uploaded new Gerbers for hardware version 2.2 (minor changes to the schematic and PCB, just part designators updated)

Update (Jan 23rd 2021): uploaded new Gerbers for hardware version 2.1 (changed from two small SRAM to single larger SRAM, firmware and software is the same)

Update (Jan 10th 2021): uploaded new Gerbers version 1.9 (added pull up resistors to the EN_RST and WE signal to improve behavior when Arduino serial port opens)

Update (Nov 18th 2020): uploaded new Gerbers version 1.8b