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)
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...)