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# Clutch Switch Config

### Tech Articles

Discussion and questions related to the course Practical Standalone Tuning

Im struggling with wiring and setting up a clutch switch with ecumaster emu black. Car is bmw e46 and clutch switch is "switching" 12v to stock ECU input, if i understand correctly Analog Input on EMU Black, can only handle 5V? Can i use different Input on EMU, or do i need to rewire whole clutch switch to use +5v.

Why don't you use a voltage divider? A voltage divider is just two resistors. Use this page to calculate what size resistors you should use:

https://ohmslawcalculator.com/voltage-divider-calculator

Assume your input voltage is 15V (battery fully charged, or charger attached with bad regulation), you want to produce 5V maximum in this situation.

So if you enter 15 in the top box, and say 10k (10000 ohms) in the R1 box, and 5V in the output voltage box, the calculation will tell you you need a 5000 (5k ohm) resistor. Your resistors won't pass much current so you can use inexpensive 1/4watt axial resistors. To see what the output voltage would be at 12V, just enter that in the top box, delete the value in the output voltage box and click the calculate button.

Hopefully you can set a threshold at like 3 volts in the ECU Master software.

I was thinking about that, but if divider fails, then there is instant battery voltage on ecu input. I think it would be safer to just find different analog switch for my clutch and just scrap the bmw one.

I would research the specs for the ECU -- often while it measures 0-5V, it can tolerate up to battery voltage.

But you can certainly wire in your own switch, my suggestion is that the switch go to ground, and use a 5V pull-up resistor on the input side of the switch.

ECU Specs says 0-5V analog inputs, so i doubt it will tolerate 12V.

Just bought a old type bmw brake light switch, will use it as You said, switch to ground with pull-up.

Thanks for help!

I was skeptical. According the the EMU Black manual found here. The Analog inputs measure 0-5 volts but are protected up to 20V.

Over-voltage protection would be a sensible precaution for any electronic device, especially those using 5V sensors in a 12V environment.

However, as resistors are virtually failure-proof, using one to drop the voltage, or better a voltage divider, should be fine.

That said, itmay not be needed if the ECU has a simple high/low 12V option for the input?

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