Jetson NANO GPIO problem


I am using a Jetson NANO with my Jetbot AI kit. I want to install a motor wheel encoder (lm393 based MH Sensor Series FC03).

I connected the VCC to 3V3, GND to GND and D0 to many GPIO ports, but the symptoms are totally the same:

  • if D0 is not connected: HIGH
  • if I connect D0 when the sensor is covered: HIGH
  • if I remove the “cover” (so the light goes through): LOW
  • if I place the cover again it is still LOW
    Removing and replacing the cover makes the led on the sensor to go to LOW and HIGH (I guess, but it is NEVER totally off, except if I disconnect the D0 from the GPIO board), but this is not detected by the Jetson.GPIO package.

I can see that it is going from HIGH to LOW if I follow the steps above (disconnected D0, then cover + connect, then remove cover), but I am unable to change it back to HIGH, so basically my motor wheel encoder will never work.

Is it possible to fix this issue?

I am using the latest jetbot ai software with the official jetson nano OS.


hello balint.tahi,

may I know what’s your pin connections, is this module sending analog signal?
since the analog input is unavailable for Jetson Nano. you may have to add external ADC, and read this value on the Jetson Nano via the GPIO.

Hello JerryChang,

The specification of the encoder is here: link

  • Output: digital switch output (0 and 1)
  • It have the output state light, if output high level, the lights are off. if output low level ,it on.

I tried the default (, which is in the jetson-gpio package (BCM-18;PIN-12) and many others (do you need a complete list? ). Could you please suggest some I should try or do you have any possible problem in mind?

Currently I am trying to use (in BCM mode) 20 and 26 (PIN 38 and 37) for the left and right wheels, but it is the same for both of the encoders on all of the GPIOs I tried …

If the D0 (or DO … as Digital Output is NOT connected to Jetson Nano, the leds on the encoders are turning completely off, when I cover them. However when they are connected to the GPIO, the leds have some pale light still.

Thanks in advance!

hello balint.tahi,

you may refer to Jetson Nano Product Design Guide for the details info for each pin,
please also refer to application note of 40-Pin Expansion Header GPIO Usage Considerations.

Thanks. I will take a look at it, but as I said I would like to get a solution how to connect these guys rather than an electrical specification of the board.

Is it possible to somehow connect them to the GPIO of the Jetson Nano AND read out a reliable value?


hello balint.tahi,

please refer to Jetson-GPIO sample, such as, you may use the API to detect GPIO state changes. please also check voltage levels match, Jetson would normally use a 3.3V “TTL” logic level.