dropping a signal voltage proportional to signal

Question

Basically i have a car that im installing at aftermarket ecu in, The tps signal is normally a 0-5v signal (varible resistor on a 5v output from the ecu) that the ecu uses for various things, However on this car the factory ecu also would output a 0-3v signal for the tps signal to send to the awd control module in the car,

I was thinking could i splice into the main tps signal (0-5v) that goes to the ecu and send it to the awd control module, and if i did this and used resistors to drop the signal using a voltage divider circuit with r1 = 1400 ohms and r2 = 2200 ohms, this should give me a 0-3v signal thats proportional to the original 0-5 signal correct? also would this effect the signal voltage before r1, as the aftermarket ecu still needs the 0-5v signal ?

Thanks

Scott

Answer 1

This should work fine, but with one gotcha.

Basically if the potentiometer in the ECU has quite a high resistance, then your potential divider circuit (R1+R2) would load the output of this, causing the voltage to drop. In this scenario, the behaviour of the potentiometer would become roughly logarithmic which could make it much harder to control - at one end, tiny movements will translate into larger voltage changes than at the other end which may be very undesirable.

A way around this loading effect would be to use larger resistors for R1 and R2 - if you make sure that they are larger than the overall resistance of the potentiometer, it will reduce the loading. You could also use an op-amp to buffer the signal prior to your resistors, or even use it to do the attenuation.