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Topic: Are any ATmega328P input pins 5V tolerant when VCC is 3.3V? (Read 2113 times) previous topic - next topic

BlueBill

I want to connect a 433MHz RF receiver running at 5V to an Arduino running at 3.3V, or do I have to build a resistor / diode clamp.

Some (PIC) MCUs have 5V tolerant input pins but I'm new to AVR & Arduino's.

Bonus question, are any inputs better suited to capture? e.g. IR or PWM (on PIC it's called a Capture Compare module). I suppose INT inputs would do in a pinch.
Bill

retrolefty


I want to connect a 433MHz RF receiver running at 5V to an Arduino running at 3.3V, or do I have to build a resistor / diode clamp.

Some (PIC) MCUs have 5V tolerant input pins but I'm new to AVR & Arduino's.

Bonus question, are any inputs better suited to capture? e.g. IR or PWM (on PIC it's called a Capture Compare module). I suppose INT inputs would do in a pinch.



Basically no. The AVR chips use internal clamping diodes on all the I/O pins and as such if the signal input voltage is higher then Vcc +.5vdc or so the diode starts to conduct high current and damage is sure to follow. So if you run a AVR chip at 3.3vdc on Vcc then inputs must not go above 3.3vdc.

Lefty

BlueBill

Thank you. I guess the choice is a 100ohm resistor & Schottky diode clamp to 3.3V or a 3.3V 433/315 MHz module.
Bill

retrolefty


Thank you. I guess the choice is a 100ohm resistor & Schottky diode clamp to 3.3V or a 3.3V 433/315 MHz module.


There is also the method of just using a high enough ohm series resistor between the 5 volt signal to the input pin that will limit the current flow to a safe enough value to not damage the now conducting high side clamping diode. I don't recall what that value is  for a 5 volt signal using a Vcc of 3.3 volts, but it is a valid method to use and have seen it described in various AVR and PIC application notes I've stumbled across in the past.

Lefty

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