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A way to program and live-prototype with your Attiny85 with one board, without having to move the chip around.

What’s it all about? Well, I was doing some programming and prototyping with the Attiny85 for my other project and figured out, that doing it all on a breadboard is rather tedious, compared to using a dedicated Arduino board. I had to build a programming breadboard (connected to Arduino UNO configured as a programmer), build my prototype and move the Attiny back and forth between the 2 boards to test various iterations of my software.

So I decided to make a little more efficient solution to help myself with further projects. And thus a little board was born. It combines some ideas from this tutorial: and from various people on Reddit and Facebook (thanks guys!). The main features are:

- works as a hat for Arduino UNO (very easy to connect & disconnect);
- allows for live code uploading to the Attiny, thanks to the “ArduinoISP” sketch;
- has some status diodes to help the programming;
- allows for prototyping without the need to remove the Attiny from the board (a continuous upload-and-test workflow), thanks to a header that extends all the pins of the housed Attiny;
- allows to reset the Attiny.
Building it is pretty easy, so let’s get to it!

- a universal board (at least 3x7 cm) or a dedicated PCB;
- 3 LEDs (LED1-3);
- 1 tact switch (KEY1);
- 1 10μF capacitor (C1);
- 1 0.1μF capacitor (C2);
- 1 DIP-8 socket (under U1);
- 1 8-pin female header connector (or 2x 4-pin) (H1);
- 3 330 ohm resistors (R1-3);
- breakaway male header connector (at least 12 pins);
- a breadboard and some more DuPont wires for prototyping (optional);
- soldering iron, soldering wire, flux, desoldering pump (optional);
- Arduino IDE (or other similar platform);
- additionally: Arduino Uno & Attiny85 (without them the board is quite useless :-) ).”

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