I am trying to add a flow sensor to the Pixhawk GPIO as described in Fuel Flow and Level Sensors — Rover documentation but face the challenge of getting the right Voltage levels. Which i guess is related to a Pullup-Pulldown issue.
My sensor provides a nice PWM in a “dry” setup with a 1,5k pullup 5v power supply.
However, when plugging into the Pixhawk V3.0 the pullup seems to fight an internal pulldown. The voltage drops to about 0.9V. It still provides a good pwm but with the wrong levels.
After some searching in the docu I tried 2 things so far: Base on Buttons — Rover documentation I tried removing the pullup completely since it states that
These pins will have an internal pullup assigned to them automatically,
that did not work. It was a bit like a very noisy PWM on 5V level.
based on Fuel Flow and Level Sensors — Rover documentation I tried a pullup to 3.3V with a 10K even though that does not comply with the specs of my flow sensor.
Any GPIO capable pin on the autopilot can be used to connect to the sensor’s output. If it is an open-collector output, a 10Kohm external resistor pull-up to 3.3V will be required
This also did not give me the desired result just a very low level PWM at around 0,3V
I have no idea about the inner schematics of the Pixhawk, maybe someone in this forum has a good idea, thanks!!