Frequency to Voltage Converter for Ethanol Sensor

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Thread Starter


Joined Nov 14, 2011
Hello all, I have a basic understanding of electronics. I have built circuits and designed a couple simple schematics for myself in the past. But I have come across something that is a little above my knowledge and I was wondering if I could get some help with it.

I am reprogramming a Subaru ECU to take input from an ethanol content sensor and use it to adjust fuel trims and ignition timing. I have an available port on the ECU that takes a 0v-5v input, but the problem is the ethanol sensor outputs in square wave frequency. The output of the sensor is 50hertz for 0% ethanol and 150hertz for 100% ethanol. So I need to build a small circuit to convert this into 0v-5v so that the ECU can read it.

I would like to use a lm2907 (or lm2917?). At first I was going to run a Vcc of 5v but later found out that I would need to run a higher value so I guess 12v it is. But the vehicles 12v source fluctuates a lot (12v-16v) so I'm not sure how I would keep that from effecting the output voltage of the circuit. Also I need to figure out a way to limit output voltage to 5v so that it doesn't send too high of a voltage to the ECU. What do you guys think?

Here is a link to info about the sensor (about halfway down the page under "Fuel Composition Sensor Description"

And the lm2907 datasheet

Thank you



Joined Apr 5, 2008

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