Interface with a pinball machine

Using Arduino Project Guidance
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I need my Arduino to see when a motor turns on in a pinball machine (the "Time Machine" motor). The motor is 24V AC and is activated from a 20V DC signal to a relay board (+20V is constant, switched with ground). Right now I have a current switch on the 24V motor input. While this works, the switch is expensive and bulky, looking for a lower cost solution.

My next idea is to use a solid state relay triggered with 24V AC (~ $15). The relay board has a pigtail connector where I can tap into the wires (I do not want to cut/splice wires on the pinball machine). The pins and Molex housings to make the tap will probably be ~ $15 so this solution is ~$30. Any ideas for a cheaper way to read when the motor is on?

AP TimeMachine
AP TimeMachine1195×464 90.1 KB

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The motor will make a field that a cheap Hall switch -may- detect from very close. Ditto for any relay inside.

1 Like
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Hi, @Mamushka

Try an opto coupler across the motor relay coil?

Tom.. :smiley: :+1: :coffee: :australia:

3 Likes
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Thanks for the suggestions, gives me some ideas to try. :slightly_smiling_face:

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24v ac relay on the motor but.......if it doesn't turn you're out of luck.
A small magnet on the motor shaft with a reed switch will give a pulse to Arduino and verify it is actually turning.

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You could connect that "switching" ground to arduino input. Put diode in series to protect arduino in case there are pullups on that line. Optocoupler is a good option as well.
Or ACS712-module...