inputmicrocontrolleroutputraspberry pivoltage
I have a microcontroller and a Raspberry Pi, both running off of the same 5v supply, in parallel. The microcontroller has 4 5v output pins and the other is a Raspberry Pi, that can only accept inputs of 3.3v and less.
Obviously I cannot directly connect the outputs to the inputs – that'll fry the Raspberry Pi.
How can I connect 5v outputs to the GPIO pins on the Raspberry Pi?
It is not guaranteed to work. You could use a level converter chip xx145, or you could use a 74HCT595, which will accept valid TTL levels at the inputs (and a 3.3V CMOS chip will give you that).
Edit: The margins are fine for 3.3V input, as alexan_e mentioned. See below.
Note that you should not connect any outputs form the HC595 or HCT595 directly to the 3.3V circuit.
A simple single-transistor level shifter was discussed here:
If you use a MOSFET you don't need the base resistor, so it can be even simpler.
This should work fine. As long as the 3.3v high level is high enough to register as a high level on the AVR, this should work correctly.
You should also add series resistors for current limiting so that the 5v level from the AVR pins do not damage the input on the SoC.
Best Answer
Use a level translator such as the one sold by sparkfun.
Hook one VCC to 5V and the other to 3.3V on the Rasberry Pi.