Interfacing 5V with PI GPIO.

[lilzz]

The SRF02 ultrasound runs at 5V, but it seems safe to connect its output directly up to the Raspberry Pi’s 3.3V I2c bus, which saves the headache of having to convert from 3.3v to 5v in both directions on the same two wires. I guess this didn’t blow up my Pi because the I2c pulses are relatively short and infrequent so don’t transmit too much excess energy for the Broadcom chip to dissipate as heat. Health Warning: overloading voltages like this can destroy your Pi, be careful!

what does this mean? OK to interface 5V I2C or not?

[joan]

No, it is not safe to feed 5V into the gpios.

However the SRF02 does not feed 5V into the gpios.

The SRF02 may be powered from 5V. It does not provide 5V to the I2C lines. To transmit a 0 bit it pulls the I2C lines down to ground. To transmit a 1 bit it lets the line float up to the 3V3 pull-up provided by the Pi.

As long as an I2C device does not have pull-ups, or its pull-ups are not to a voltage higher than 3V3 it will work fine with the Pi.