I want to read the data line from a device that normally interfaces with a controller. It has 3 pins, 3.3v power, gnd, and data. I don't need the power line since the Arduino will be USB powered and I obviously don't want to just connect it straight to ground. What would be the best way to handle this without introducing extra hardware components. Can I just connect the power to an input pin, and then I can use that to see if the device is on?

I'm using an Arduino Mega2560

  • What is the "device that normally interfaces with a controller"? If the device is meant to talk to a controller or Arduino and provides power, ground and data, it's likely that you now need to provide the 3.3V so the device has power to operate. But perhaps it's a passive device? Tell us more. Commented Apr 14, 2019 at 2:12
  • 1
    No, I'm connecting to the controller socket of a Nintendo 64. The Nintendo is powered, and normally supplies power to a controller. I want my Arduino to be a controller.
    – Makaque
    Commented Apr 14, 2019 at 2:16
  • Only connect data and gnd. Assuming the data pin is an output of the N64 and the Arduino only reads it. Otherwise you would need some voltage shifting circuit, as the N64 is 3.3V and the Mega is 5V. Beside that, I'd add a resistor between the data and the arduino INPUT, so you can't damage any of the two device if they aren't power on and off at exactly the same time.
    – Gerben
    Commented Apr 14, 2019 at 16:04

2 Answers 2


You don't need to "discard" power. You just ignore it.

If you don't need a connection, then don't connect it. The only important connection is the ground connection. Everything else can be used, or not used, at your discretion.

There's nothing "magical" about a power connection. It's just a voltage that comes from a source that happens to be able to provide more current. If you want to use it to power something, you can. If you want to just sense what the voltage is, you can. If you want to ignore it, you can.

It's not like a mountain: just because it's there, it doesn't mean you have to climb it...


I believe you want to check whether your device is on or not without drawing power from it. Something like the following circuit could be useful:


simulate this circuit – Schematic created using CircuitLab

R2 limits the current going into Arduino input pin. Resistor with value around 1K should be good given the voltages you mentioned. Arduino can read the input pin to see whether the device is on or off.

R1 pulls Arduino input pin to ground in when the device is off. This gives a "0" value at the input pin. R1 can be a high value ~10K. High value would limit current leakage to ground via R1. Though this answer won't exactly satisfy your requirement of not using additional components.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.