## Converting from resistance to voltage

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paulbutcher
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### Converting from resistance to voltage

Forgive what is, I'm sure, a dumb question.

I'm switching to a Bosch oil temperature sensor. The datasheet gives calibration information in ohms:

http://www.bosch-motorsport.de/content/ ... 0EQ3EZ.pdf

But clearly I need to configure my RaceCapture in volts. I'm sure that there's an easy way to convert from one to the other - perhaps someone would be kind enough to enlighten me?

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BigLobsterDude
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Paul,

No such thing as a dumb question.

Basically you need:
- Ohms Law (voltage = current * resistance) (note: units are volts, amps, ohms respectively),
- Series resistance rule ( Resistance Total = Resistance1 + Resistance2), and
- an understanding of the complete circuit.

Your entire sensor circuit needs to look something like this:

5 volt supply --- pull-up resistor(R1) --- temp sensor(Rsensor) --- ground

Your RCP measures the voltage at the connection between R1 and Rsensor.

So what's a reasonable resistance for R1? Your datasheet suggests 1000 ohm is a reasonable value.

The voltage the RCP measures will be: Rsensor / (R1 + Rsensor) * 5 volts

Assuming R1 is 1000 ohms, than your voltage at a given temperature is:

30 deg (C): volts = 3.2 = 1707 / (1000 +1707) * 5
100 deg (C): volts = 0.8 = 187 / (1000 + 187) * 5

Hope this helps

John Robertson
Schumacher Taxi #189

paulbutcher
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Thank you! Much appreciated.
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