Want an ATtiny85 and an Arduino Uno communicate together?

Hi there

I'm not an expert in the Arduino environment.

I've realized my own, small project on an Arduino Leonardo. After all went well, I decided to "migrate" the code to an ATtiny85, because the Leonardo is somehow an overkill for my small project.

I programmed the ATtiny85 within der Arduino IDE an all went well. But I realized, that I cannot debugging on the ATtiny85 using the Serial Monitor to observe data and get some variables.

So I dealt with I2C or TWI respectively and found many hints and tips within and outside this forum, e.g. this one.

But I'm still slightly confused how to start the right way; how can I establish a communication with I2C / TWI between my ATtiny85 and my Arduino Uno or Leonardo respectively (only during development an for debugging purposes)?

Hope my question is not very silly... :confused:

Regards Roman

If it's just for debugging purposes it may be worth implementing some sort of SoftwareSerial that just transmits on one pin. Then you can connect directly to the PC with a USB-TTL converter.


Yes, only for debugging purposes. I really only need to get to content of some variables during the development of an ATtiny85 sketch.

Your hint sounds very interesting, but - to be honest - it is too high level for me. :frowning:

What do you mean with “…some sort of SoftwareSerial”? And how can I use it together with an “USB-TTL converter”? How should I imagine this “USB-TTL converter”?


You buy a USB-TTL converter. One end plugs into a PC's USB port and the other end has Rx Tx and GND etc connections.

This Thread may be of interest. I have a feeling I wrote an even shorter "send only" version that uses very little SRAM but I can't find it right now. Probably I just deleted all the Rx stuff.


Thanks a lot.

A USB-TTL converter is ordered and on the way to me... ;-)