ATtiny85 breakout boards

The ATtiny85 is one of the smallest microcontrollers in the AVR ATtiny series. In a SO-8 package it’s the size of a small opamp, perfect for tight boards. It’s not much of a beast though, with effectively only 5 free I/O pins, but surprisingly often that’s just enough.

Tiny MCUs like this come especially handy for prototyping, where you might just want to try something that needs a couple of control voltages, and the bulky Arduino is already hooked up to some other ongoing project. So I drew up some breakout boards and ordered them from DirtyPCBs. Leds and buttons come handy too, so I added one of each…

Since most forces will be exerted on the ISP connector and the button, I placed those in the middle of the pins. The ISP connector has the standard pin layout, and any AVR ISP programmer will work. Most components are 0603, only the 10uF cap has a bigger footprint.

If you like the boards, order the PCBs from DirtyPCBs!

The schematic is like this:

Only one of the two resistors “RESET H” or “RESET L” should be placed; “H” pulls reset up to VCC, “L” down to GND. I used 10k for these. R1-R3 can be smaller, such as 1k ohm; these resistors are in place so that the ISP connector can work correctly when the board is connected to the prototype breadboard.

My breadboard prototypes invariably turn into these messy knots of wire… here the ATtiny85 drives an ENC28J60 ethernet controller (and some extra stuff):