In essence, the Digi-Comp I contained three mechanical flip-flops, providing an ability to connect them together in a programmable way using thin vertical wires that are either pushed, or blocked from moving, by a number of cylindrical pegs. The whole arrangement was ‘clocked’ by moving a lever back and forth. Different configurations of these cylinders caused the Digi-Comp to compute different boolean logic operations. With a three binary digit (3-bit) readout of the state of the flip-flops, it could be programmed to demonstrate binary logic, to perform various operations such as addition and subtraction, and to play some simple logic games such as Nim.[1]

Original Manual [PDF]:

3D printable version, another example:


Interesting. So this is the type of logic that things like pinball machines used. You have solenoids, relays, and cams with contacts. Similar things used things such as decoders (mechanical position sensors), motors, and servos.

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