GPIO input voltage from sensors - need clarification

Question

I apologize if this has been answered, I couldn't find any definitive answer.

I wanted to connect ultrasonic range sensor (based on this tutorial http://www.modmypi.com/blog/hc-sr04-ultrasonic-range-sensor-on-the-raspberry-pi) but here the author notes that you need some resistors to limit the 5V output the sensor is sending.

This info is kind of new to me and I didn't care when I was connecting previous sensors. Apparently PIR ones also send 5V outputs when they detect movements. I have been using those sensors for some time.

So the question basically is. Can Pi handle 5V input on GPIO pins or it could damage it? Thanks.

I have version 3 and also Zero.

Answer 1

The Pi's GPIO are all 3V3.

There appears to be limited protection for higher voltages such as 5V but the advice will always be use a level converter (such as a voltage divider) if you can.

If you must connect 5V direct to a GPIO use a series resistor to limit the current to about a quarter of a milliamp (0.00025 amps). The protection circuitry should be handle that sort of load.

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Most of the hobby PIRs I've seen output 3V3 even when powered by 5V.