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cosmac elf

The next step in my homebrew computer adventures is the Cosmac Elf. The Cosmac Elf was a DIY computer that appeared in Popular Electronics is 1976 and 1977 using the RCA 1802 microprocessor.

The schematics that I used are here. ELF Schematic 1 Elf Schematic 2

Other good resources can be found here:

I was able to find all of the parts except for the TIL311 displays. Well, I could find them, but the cheapest I saw was $30 per display, so I ended up using regular 7-segment displays with an arduino driving them. The arduino code is below.

The code runs a timer based interrupt and each pass reads the data from the bus, and outputs the correct character to the 7-segment display. That’s all it does really. There are probably better ways to do this, but this works and I didn’t spend too much time on it. You can see the arduino hiding in the hideous mess of wiring below.

Below is a quick video demo of a program that reads the input from the switches and outputs them on the 7-segment displays.