I'm working on a project that uses a raspberry pi as a music player but some of the controls are going to be handled via an Arduino Nano. I need to pull GPIO 4 on the Raspberry Pi LOW in order to mute the audio. However, the Raspberry Pi uses 3.3V as a logic high so I don't think I can hook up a 5V pin on the arduino to it. Is there a way to set the Arduino pin to put out 3.3V instead of 5V on a specfic pin? What are my options here?

Probably the simplest solution is to use a resistive divider to scale the rpi input to 3V

The BSS138 (a type of mosfet) with two pullup resistors is a common level shifting method, I think adafruit sells a board with a few of these on it, or you solder a BSS138 and the necessary resistors to a board of your own if you're designing a custom PCB. Th BSS138 is a bidirectional level shifter, the same circuit can be used just as easily when the Pi's pin is and output and the arduino's pin is an input as when vice-versa. You need one BSS138, and two resistors, for each separate data wire run between the Arduino and the Pi.

Assuming the Pi pin has an input pullup, I think you could do this, but I'm not certain as I've never tried doing it. Hopefully someone will tell us why it's wrong, or confirm it's okay. const byte piPin = 2; // Change to the pin you want to use void setup() { pinMode (piPin, INPUT); } void loop() { // Call piPinLow() when you want to set it low // Call piPinNotLow() when you want to set it to not be low } void piPinLow() { digitalWrite(piPin, LOW); // Probably not necessary pinMode(piPin, OUTPUT); } void piPinNotLow() { pinMode (piPin, INPUT); } My rationale is: When the Arduino pin mode is INPUT, it's floating, so as far as the Pi is concerned it won't see any voltage from the Arduino and the Pi's pull up will cause the Pi to see a high on its input pin. When the Arduino wants to take the Pi pin low, it changes the Arduino pin mode to OUTPUT, having already set the pin to low. The Arduino should never set its output pin to high, and the Pi should never receive 5V from the Arduino

Now that's an interesting idea.. Definitely curious to hear others thoughts.. would save me some soldering time and board space for sure.

So in your haste to get everything working, you accidentally wrote some code that set the output high.

[image] hoss75: Now that's an interesting idea.. Definitely curious to hear others thoughts I was curious enough to try it. I modified the code to include a signal to trigger my oscilloscope when the Nano was rebooted. The commented out lines aren't necessary, the Nano is already in that state by default after power up. const byte piPin = 2; // Change to the pin you want to use const byte scopeTriggerPin = 3; // For Oscilloscope only void setup() { // digitalWrite(scopeTriggerPin,LOW); // For Oscilloscope only pinMode(scopeTriggerPin, OUTPUT); // For Oscilloscope only delay(100); // For Oscilloscope only digitalWrite(scopeTriggerPin, HIGH); // For Oscilloscope only pinMode (piPin, INPUT); } void loop() { // Call piPinLow() when you want to set it low // Call piPinNotLow() when you want to set it to not be low piPinLow(); delay(10); piPinNotLow(); delay(10); } void piPinLow() { // digitalWrite(piPin, LOW); // Probably not necessary pinMode(piPin, OUTPUT); } void piPinNotLow() { pinMode (piPin, INPUT); } This is how I wired it: [image] This is the oscilloscope trace after pressing the reset button on the Nano: [image] [Edit: I forgot to add a conclusion, which is that it works in the way I expected it to]

Controlling Rasperry Pi Pin from Arduino

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EmilyJane May 14, 2025, 1:17pm 10

As long as it's impossible for the Arduino to ever set its output pin high.

Does switching pinMode from INPUT to OUTPUT produce reliable output LOW?

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Controlling Rasperry Pi Pin from Arduino

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