Relay Notes

If you’re following along at home here are some initial notes and designs for the ALU portion of the computer.

First up is this sketch of how relays will be used to create the various gates used. There is an inverter, a 2 input AND, a 2 input OR and a 2 input XOR. Making the 3 input versions of the OR and the AND are easy in that you simply add another relay in series or parallel as indicated.

Next up is my design for the full adder. This is a traditional design using 2 XOR gates, 2 AND gates and an OR :

Next is a 3 input Multiplexor. This will select an input (A, B or C) using the S0 and S1 inputs. This is a big unit and uses 16 relays to do its job:

When we put all this together we have the basic logic design for one bit of the ALU. There will be 4 of these units, each one on its own board in the ALU unit.

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