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VoltageDivider (voltage across resistor to GND when another resistor present to +5V). See http://www.ohmslawcalculator.com/voltage-divider-calculator Example * 5V * 2700 Ohm (R1) (typical MAT pullup for NTC type MAT sensor) * 1000 Ohm (R2) * 1.35 V output = '''5/(R1/R2+1)''' Example * 5V * 429 Ohm (R1) (typical MAT pullup for PTC type MAT sensor) * 1000 Ohm (R2) * 3.5 V output = '''5/(R1/R2+1)''' So '''easy to decide what kind of pullup is inside the ECU''' (analog input, trigger input, wheelspeed input or MAT input): with '''just 1 measurement''' (using known resistor, or sensor with measured known resistance at the actual temperature) EasyTherm/SensorTable shows a table: typical voltage values for different R2 (=NTC sensor resistance values): with R1=2700 Ohm pullup resistor ---- '''Parallel resistors (not voltage divider; actually same voltage)''' * '''510 replus 2700 = 429''' = 1/(1/510 + 1/2700) = 1/(1/R1 + 1/R2) ** For example a 2700 Ohm pullup resistor inside the ECU, ** and an 510 Ohm (physically inside or outside, parallel either way) pullup resistor to +5V ** is '''equivalent to 429 Ohm''' (roughly 430 Ohm) '''resistor'''. * Hint: if ECU was ordered with standard MAT input (not requesting special PTC type MAT input) an external 510 Ohm "pullup" resistor to +5V can be used for more precise MAT reading (otherwise PTC calibration would not be very precise...) ---- '''Hint''' : [http://jansson.us/resistors.html resistor values, resistor ratio and voltage divider calculator]
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