I2C - Pullups and Voltages

[espruino-discuss2]

Posted at 2014-05-05 by mgg1010

Hi

I've been attaching my Espruino board to my existing I2C busses which have previously been tested with Arduino and other devices.

One interesting question is bus voltage: the I2C devices I'm using are on PCBs that require a 5V power supply. In the past, I've connected up a 3.3v Arduino - I just used pullups to 3.3v instead of 5v, and this worked. But it didn't work work with Espruino.

Then I realized that the Espruino pins used for I2C are 5V tolerant, so I've changed the pullup to connect to 5v - and it seems to work now :)

However, I am using 2k7 pullups, which I suspect may be a bit too low. I think the general advice is 4k7 to 10k?

Thoughts?

[gfwilliams]

Posted at 2014-05-06 by @gfwilliams

Yes, so most pins on Espruino (apart from ADC pins) are 5v tolerant and pulling up to 5v is fine. Personally I use 4k7 pullups to 3.3v, so it may be that just having a 3.3v pullup with a higher resistance would be fine for you?

Having said that I've only tried maybe 5 different I2C devices, so some of them may require that 5v pullup.