Speedo sensor wire tap

[Neophyte]

I am trying to tap into the speed sensor for some data logging and displaying on an Android device.

I am looking for tips on getting a good clean signal from the speed sensor wire.

If I put a LED onto the signal it isn't totally on and off but dim and bright. If I put a pull-down resistor on then I get on and off BUT then the stock speedometer shows nothing. This dim/bright scenario then obviously makes the transistor I use, to get a signal to the Arduino, always see an "on" state.

 

[ottafish]

Use an basic op-amp to drive the resistor.

 

[Neophyte]

Use an basic op-amp to drive the resistor.

Thanks. Not to be spoon fed or anything but unfortunately my electronics knowledge is quite basic and don't really know op-amps. BUT I will go an research myself too. It helps just to be pointed in the right direction.

 

[Boosted Cycle Perf]

The signal from the seed sensor is not a voltage based signal. It’s a frequency.

For future reference, when tapping in to factory sensors to grab signals to datalog, pull-up resistors are only needed on 2 wire sensors like the engine coolant temp sensor. 3 wire sensors like the speed, or map sensor you can connect directly to signal wire.

 

[Neophyte]

The signal from the seed sensor is not a voltage based signal. It’s a frequency.

For future reference, when tapping in to factory sensors to grab signals to datalog, pull-up resistors are only needed on 2 wire sensors like the engine coolant temp sensor. 3 wire sensors like the speed, or map sensor you can connect directly to signal wire.

Cool thanks for the tip.

Yes, I do understand it is a frequency based signal but my problem is to get a good clean pulse. Getting a clean pulse from the RPM was not a problem but speed not so easy