Inside an Electromechanical Pinball Machine, Part 2—Relay Logic

Implementing all of the scoring and play gimmicks built in to electromechanical pinball machines at their apogee with ratty AC relays and stepper switches took a great deal of cleverness and respect for the limitations of these devices. It is almost painful to watch the sparks and arcs as these relay contacts make and break circuits many times per second, but the tacky-looking hardware was admirably robust and kept on working for remarkably long between breakdowns. The design also employed redundancy where possible, to allow it to soldier on in the face of dirty contacts, intermittent switches, and transient mechanical failures.

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