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Switch design question

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New Member
I apologize for my ignorance in the electronics field up front.

What I want to make is a switch that is triggered based on the TP(throttle position) sensor on my motorcycle. What I know is that the input is spec 4.5v-5.5v and tested I am getting 5.01v. The sensor has 3 leads which when tested for resistance give: (leads in order on sensor-1 2 3)

Throttle is closed

Throttle is wide open

Lead 3 seems to be the input(+) and I am not sure how the other two leads relate. The way the sensor and connector are set up I can't test it while in operation without stripping the wires. But I may do it anyway.

I want to turn a device on (which is connected directly to the ignition) when the throttle registers as wide open.

Thank you for any help, ideas, or suggestions!!


New Member
Ok, I tested the sensor during operation and it gives an output of 4.6-4.7v while at full throttle.

The load of the device will be 12v ~25Amp, which needs to be switched on when the TP sensor reports ~4.6v and switched off when it drops below ~4.6v.


Active Member
Things that I'd worry about are related to reliability, safety, preservation of your investment.

1. What happens of the device is triggered on too soon?
2. What if the TPS or signal fluctuates ever so slightly so that the device toggles on/off quickly.
3. How temperature and other varying conditions affect things. Have you addressed electrical noise or transients, mechanical vibration, etc.
4. Are there conditions when the TPS could look like or actually be wide open but you would not want to turn the device on?
5. If the TPS or a wire related to it fails, will it turn on, if so, is that bad?

If none of this is a problem then a simple circuit may be appropriate. If there are other worries such as I've mentioned here (there certainly could be plenty more) you might employ a microcontroller or similar electronics to address the issues.


New Member
Those are great questions

1. I'm not worried about it
2. It would be an annoyance, but the only thing it would do is probably wear the device out faster
3. This one I don't know, it will get quite warm but I plan to have the circuit/relay/switch away from the engine compartment so hopefully it will alleviate some of those possibilities.
4. I have a kill switch that turns the whole thing on and off directly from the battery.
5. It wouldn't be good, but I could use the kill switch.

This is for a very experiment device that I am using this switch to test it with while doing performance testing so it wont see alot of action. I've been looking at relays and everything I find that can handle the current (30A) requires too much voltage to turn on and anything that needs teh correct voltage to turn of wont turn off until around 1v and can't handle more then 1A of current.

It needs to handle 12v at 25-30A (more is even better), switch on at ~4.3v and switch off at ~3.0v. I can't find a relay that will do this...any ideas?
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