SparkFun Forums

[seawood7]

Morning, I am new to this forum so howdy folks

I am running the Arduino 1.8.0 IDE on Windows 7 ( probably irrelevant).

I am messing around with a project that will potentially use 20 arduino i2c slaves to drive a whole bunch of led arrays

I am looking at the Leonardo pro micro (5v) (LPM) which in most ways is ideal for my needs ( low cost and DIL package ).

I have hit a snag, I2C works just fine as a master, but will not work as a slave.

I have tried it with another LPM as master and also with with a arduino uno as master. no receive event is generated. I have confirmed that my wiring and sketch works fine, if I run the receiver on the Uno and the master on the LPM it works fine.
I also have the LPM working as a master with a BMP180 weather sensor.

I don't have the experience to hack the source libs, so has anybody found a way to get the LPM to work as a slave, or suggest an alternative low cost tiny arduino compat that has working I2C

kind regards
Pete

[darrellg]

Do you have 4K7 pullups on the SDA and SCL lines?
https://learn.sparkfun.com/tutorials/i2 ... ware-level

[seawood7]

Yes indeed I do.

According to this doc http://www.ti.com/lit/an/slva689/slva689.pdf - for TI's implementation of i2c, 4k is about the lowest reqd resistance.

The 2 devices are 2cm apart, the wires between them are 6cm long, and 3mm apart, so far higher resistance pull ups should work.

I have i2c working fine with a number of configs, so I think it's a problem withe the leonardo micro i2c libs.

Pete

[seawood7]

doh

I had pull up resistors pulled up to sky, the 5v line on the breadboard had come part out of socket, pushed it back in and it all sprung to life.
I found it then worked happily with 15k resistors.

Pete

[darrellg]

Glad you were able to figure it out. Most I2C issues are pullup related.