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Thread: Program pin set from RPI GPIO

  1. #1
    Junior Member
    Join Date
    Dec 2019

    Program pin set from RPI GPIO

    I've got a Christmas light display in my front yard that I setup using a teensy 4.0 and FastLED. It's worked well. I also have a raspberry pi 4.0 at the tree that I use to modify the code and upload to the teensy. (I access it over NoMachine over wifi.) Sometimes some of my sketches will 'crash' the teensy, or at least that's what I think is going on. After I load them it doesn't work and I can't program again without going out and pushing the program button on the teensy. That is a bother that I thought I could remedy by hooking up one of the GPIO pins on the Pi to the program pin on the teensy. I believe it is active low. I wrote a little python program on the Pi to toggle pin 8. I thought the GPIO pins are high impedance, but whenever the pin is connected the Teensy reboots constantly. Am I doing something else wrong or do I need a pull-up resistor on the program pin?

  2. #2
    Senior Member
    Join Date
    May 2015
    San Francisco
    Your assumptions sound correct. The program button on T4 just shorts the program pin to ground. Assuming you have a solid shared ground and a high impedance GPIO on the Pi, pulling that pin low should cause the teensy to trigger programming. Can you check the voltage on that pin with a meter or scope?

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