Speedlimiter circuit using lm2917 ..#2

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Joined Aug 1, 2022
See the attached schematic.

SW1 is actually your reed switch; it's normally open and closes for a brief moment when a magnet on a wheel passes by. I used a relay and signal source so that I could simulate it.

R2 is where you set the speed limit. Once you find the correct setting, you should really remove the pot, measure it, and replace it with a fixed resistor, as pots are not as reliable as fixed resistors.

U1 has a time-out of about 95mS when R2 is adjusted properly. If triggers from the reed switch occur too often, U1 does not time out, and it's output never goes low. This causes U2 to time out a short time later, and its' output goes low, energizing the relay.

As shown, the output to "points" would be connected to the high (coil) side of the points, but that might result in the coil getting overheated. I don't know what arrangement you have for your ignition, but a relay could be wired up in whatever arrangement that's appropriate for your ignition - perhaps to disconnect power from it.

If your scooter is fuel injected, it would be preferable to interrupt the injector circuit. Otherwise, when the ignition system is disabled, you will be dumping a raw air/fuel mixture into the exhaust system that is extremely flammable, and will likely ignite with a loud "BANG!" when the ignition is again enabled.

I build your circuit, and now I'm trying to test it in bench.

I don't have reed switch yet, so I'm testing without it. When I turn power on, relay is energized instantly and circuit use some power. If I connect voltage meter to GND and U1 trigger pin, it show about 1.5v and circuit using power drops but relay is still energized. I have oscilloscope and pulse generator, can I trigger U1 directly with that for bench test until I get reed switch?

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