i2c and barebone


I'm trying to use the i2c bus on a self build 'bare bone arduino' with the atmega 328p chip (with uno bootloader). I used the instruction for the bare bone from the following website:


I uploaded the Wire example sketch but nothing happens.

Do you need some additional hardware to use i2c on the 'bare bone' setup?

Thanks in advance

No, it should be working.

The capacitor from reset to DTR should be 100nF. And an extra 100nF is needed as decoupling capacitor near the ATmega chip to 5V and GND.

Can you make a led blink ? To be sure that it is running ?
Which I2C device did you connect ?

Thanks for your reaction,

I have 2 'barebone' arduinos of one I use as slave and one as master. But I can't make it work with i2c. The 'barebone' works ok, digital in/out, analog and serial all work. Uploading a sketch works but only no i2c...

I have in the power supply a 100nF between 5V and GND (which is next to the chip).

Show us the sketch for both the Master and the Slave.
A common mistake is to use a Serial function in the interrupt routine, or use multiple Wire.write in the interrupt routine.

Did you know that you can start two Arduino IDE instances, both connected to an Arduino (or barebone) and both with a serial monitor. So you can develop and test both at the same time.

I made two other barebone's and the i2c comm of them works. So i think its a hardware problem. The arduino freezes when I connect the i2c wires. When I upload the same code on the other barebones it runs without a problem.

I will check my soldering...

What kind of wires do you use for the I2C ?

You can only use short wires for the I2C bus. The total length (total length of all wires added) can be about 2 meters, but only when the wires are seperate wires. When the wires SDA and SCL are next to each other in a cable, perhaps the total can be only 50cm.

Solved: little crack in the isolation of the SCL wire on the circuitboard. ::)

You found the problem. Nice 8)