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Test programming the ATtiny85

Just got my ATtiny85 chip today from the postman and playing with it now.

There are quite a number of ways to program the ATtiny85, from the very cheap (USBasp, Tiny AVR Programmer, USBtinyISP) to the more expensive (AVRISP mkII). The Tiny AVR Programmer is probably the most convenient of the lot because it targets the ATtiny family specifically, so no cables are required. Just plug the chip into the provided socket.

Since I already have a spare Arduino Uno lying around, I am going the no-cost way, using the Uno to program the ATtiny85. You basically need to hook up the Uno to the ATtiny85 on a breadboard via 6 jumper wires. It's actually easier than it sounds, and took all of a couple of minutes to do.

Configuring the Uno to become an ISP

The next step is crucial. You need to upload a sketch to the Uno so that it has the necessary code to become an ISP. That's how you can then program the ATtiny85 through the Uno.

The first step is to load the ArduinoISP sketch from the built-in examples:

Make sure you have the board type selected as "Arduino Uno"

Now click "Sketch, Upload" and the upload should be completed without errors.

Installing ATtiny85 support

Under "File, Preferences", in the "Additional Boards Manager URLs" field, add this URL:

Then under "Tools, Board. Boards Manager...", type in "attiny" in the Filter field. You should see "attiny by David A. Mellis". Select and install.

Now that we have ATtiny85 support, under "Tools, Board", scroll to the end of the menu and select "Attiny 25/45/85".

Under "Tools, Processor", select "ATtiny85".

Under "Tools, Programmer", select "Arduino as ISP".

We are now ready to program the ATtiny85! Open up the sample "Blink" sketch:

 Change all references of LED_BUILTIN to 1. So the code looks like this:

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(1, OUTPUT);

// the loop function runs over and over again forever
void loop() {
  digitalWrite(1, HIGH); // turn the LED on (HIGH is the voltage level)
  delay(1000); // wait for a second
  digitalWrite(1, LOW); // turn the LED off by making the voltage LOW
  delay(1000); // wait for a second

Select "Sketch, Uploading Using Programmer" to upload the compiled sketch to the ATtiny85. Using "Upload Using Programmer" is important, as it indicates to upload the sketch through the Uno which we have setup as an ISP.

Once the sketch is successfully upload, we can connect a LED to the ATtiny85 (longer lead (+) to Pin 1, shorter lead (-) to GND) and watch it blink.

► Breadboard diagram created using Tinkercad.
► Source code formatted using ("manni" style).


  1. Arduino: 1.8.9 (Windows 10), Board: "ATtiny25/45/85, ATtiny85, Internal 1 MHz"

    Sketch uses 956 bytes (11%) of program storage space. Maximum is 8192 bytes.
    Global variables use 17 bytes (3%) of dynamic memory, leaving 495 bytes for local variables. Maximum is 512 bytes.
    avrdude: Yikes! Invalid device signature.
    Double check connections and try again, or use -F to override
    this check.

    An error occurred while uploading the sketch

    This report would have more information with
    "Show verbose output during compilation"
    option enabled in File -> Preferences.


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