Cannot set the output pin to 0V

Robotics & Edge Computing Jetson Systems Jetson Nano
1

I want to set pin 35 to 0V, to reduce the current at the position I marked in the picture (A to GND)
So that modulate the amplitude of the pwm signal by pin 35.

  • What I expected:
  1. If I set pin 35 as input, the current A to GND increase.
  2. If I set pin 35 as output and set to LOW, pin 35 will go to 0V and the current A to GND will decrease.

  • In real:
    The voltage of pin 35 is ~0.35 V and doesn’t change. (PWM signal voltage is ~1.5v)
    When I just simply connect 35 pin - register - GND and set pin 35 HIGH/LOW, voltage of pin 35 changes.

  • Question:
    Why I cannot pull-down the signal even if I set the pin 35?
    Is pin 35 being pulled-up to the signal pin?)

Is there any solution?

3

Assume you are talking about the pin 35 of 40-pin header. Please read the 40-pin docs in DLC first. There are some requests to the external device attached to the header.

https://developer.nvidia.com/jetson-nano-developer-kit-40-pin-expansion-header-gpio-usage-considerations-applications-note

https://developer.nvidia.com/embedded/dlc/Jetson-Nano-40-Pin-Expansion-Header-1.1

4

Thanks for quick reply. I read it but I have too little knowledge about HW stuff to understand it.
I don’t even know what “level shifters”, “driving”, “buffers” mean.
Could you explain with a picture please? (ex> how should I fix the circuit)

5

After reading the document many times, I think I kind of understand.
So the GPIO pin are connected to the level shifters and if I set the GPIOs as outputs,
they are pulled up/down with the 4 k ohm registors inside the level shifters.
In my case, even if I set the pin 35 to LOW, there is a 4k ohm inside the pin so I cannot directly pull down the signal.

@Trumany
One more question! Do all the Jetson developer kits(not only Nano, Xavier NX, etc) have these level shifters inside the GPIO pin header?

6

Most Jetson have that. You can check the carrier board schematic first.