VemsAudiAan mot55/pin41 A/C idle up => voltage divider to protect mch3 (raw extra ADC mcp3208/3 ).
The assumption was : between 4.5V and 15V when AC active, and appr. 0V when off
- correct !
The mch3 has an 1 + 100k / 75k voltage divider (from EGT2 ad597 output), so
Voltage divider options (47..68k resistor in series with the "upper" 100k 0805 SMD onboard)
68k series with the 100k (in heatshrink coming from mot55/pin41) makes the voltage divider ratio:
- 1 + 168k / 75k
- Vdiv=1+168/75 ( = 3.24 )
- V=[5, 10, 12, 16]
- V ./ Vdiv = 1.54 3.08 3.70 4.94
So dividing 5V, 10V, 12V and 16V to => 1.54V, 3.08V 3.7V and 4.94V respectively (activation threshold is normally around 0.9 .. 1V). So it should clearly detect on and off condition. (and apparently it does, A/C idle up function became popular).
Alternatively 47k series with the 100k
- Vdiv=1+147/75 ( = 2.96 )
- V=[5, 10, 12, 16]
- V ./ Vdiv = 1.69 3.38V 4.05 5.41
Actual measurements - Voltage in view gauges / raw ADC ( mch3 ) when A/C clutch is on and off
mswanson: going from memory on my workbench, I had 3.3V when active, and 0v when inactive. => perfectly matches the 47k series resistor (with the 100k SMD on PCB) voltage divider above.
Worked with an inverted' control strategy on the activation channel in the 1.2.38 firmware settings for idle control AC activation
When measuring the voltage on the car the pin seems to put out somewhere around 10V (lower than VBATT of 12-14V). I think this voltage is actually coming from the a/c control head, so its probably regulated down for some reason in the OEM application.
Thanks for your measurements and notes.