@nicolaufg wrote:
Hi all,
I built myself an infrared RPM sensor (although I’m quite bad at electronics). It works well with a teensy and I can quite accurately read the RPM with a custom program for that (see here).
I then moved to a Pixhawk and it doesn’t work anymore. The settings are fine because I get the 3000rpm when I hook an RC channel, so the problem may be in the signal from my sensor. Here some data:
- An IR led lights the backplate of the propeller cone which is divided in 8 parts (4 whites, 4 blacks).
- It is a voltage divider where the upper resistance is the IR sensor (changing from 1.7KOhm to 25KOhm when going from white to black)
- The lower resistance is 6KOhm
- In open circuit, powered with 5.3V, readings go from 1V to 4.1V
- Using a voltmeter capable of reading frequencies, I can read the RPM easily
Now, when i plug the sensor to the Pixhawk (be sure settings are right cause I can read the 50Hz of a RC channel as 3000rpm when multiplier is 1), the two voltage readings are 2.2V and 3.5V and Ardupilot can’t get any RPM reading at all. It remains at -1.
As I said, I do not know too much about electronics, but… does it has something to do with pull-up and pull-down resistances? Am I missing something? I know teensies tend to make our live easier and may be missing something when bringing my sensor to the Pixhawk, but I hesitate trying things bravely to avoid frying my Pixhawk.
Cheers
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