Pre-1960, it was not rare for electronic devices to contain some kind of wheel or roller with circuit board traces on it. These traces would temporarily form connections between contacts as the wheel turned. The wheel could store a musical composition, and it could also contain more complicated kinds of programs including finite state machines.

These devices obviously fell into disuse after transistors became cheap and widely available.

I call these things rotary relays because they're rotary and they are relays. But I doubt that is the usual name for them.

Here are my questions:

  1. By what name(s) were these things commonly known?

  2. Does anyone still make them?

  • \$\begingroup\$ I doubt that such a thing would be at all common. The more common technology for "electromechanical ROM" would be punched cards or paper tape. The only common example I can think of would be the sequencer in an appliance like a clothes washing machine. \$\endgroup\$
    – Dave Tweed
    Commented Jun 15, 2023 at 22:03
  • \$\begingroup\$ I know they aren't common. I'm asking what they are called. \$\endgroup\$ Commented Jun 15, 2023 at 22:13
  • 2
    \$\begingroup\$ What you're describing sounds similar to, but not quite the same as, a stepping switch as used in early automatic telephone exchanges. \$\endgroup\$
    – user85471
    Commented Jun 15, 2023 at 22:18
  • \$\begingroup\$ It might be worth rephrasing this and asking on retrocomputing.stackexchange.com \$\endgroup\$ Commented Jun 15, 2023 at 23:25
  • 1
    \$\begingroup\$ @user85471 Those are also called Strowger switches, after their inventor. (The term more properly refers to a specific type of stepping switch, I believe.) \$\endgroup\$
    – Hearth
    Commented Jun 16, 2023 at 3:47

1 Answer 1


It's known as an electromechanical / motorised cam timer.

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It comprises motor - driven cam sets that actuate their respective switches. Each cam set may be adjusted for switch operating position and duration.

  • \$\begingroup\$ That's what I needed! Thank you :) \$\endgroup\$ Commented Jun 16, 2023 at 22:35
  • \$\begingroup\$ Anytime, James! \$\endgroup\$
    – vu2nan
    Commented Jun 17, 2023 at 3:05

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