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Flashing the ATtiny85 with an Arduino Uno

1. Upload the Arduino ISP sketch to the Uno

The sketch is included in the default examples of the Arduino IDE. It allows the Arduino to be used as a bridging device between the USB of the computer and the ATtiny chip.

To quote the Arduino website on the subject:

Serial Peripheral Interface (SPI) is a synchronous serial data protocol used by microcontrollers for communicating with one or more peripheral devices quickly over short distances. It can also be used for communication between two microcontrollers.

Navigate to File->Examples->ArduinoISP.

Upload the sketch to the Arduino Uno. It is now ready to be used as a bridge in order to flash the firmware to the ATtiny.

2. Download and install the ATtiny cores package

Theses files contain the parameters used by the IDE to compile and upload the sketches to the various chips or microcontrollers compatible.

Several are already included, you can find them under Tools->Board. The ATtiny was unfortunately left out so we need to add it manually.

Install on Arduino IDE >= 1.6.4

The new version of the Arduino IDE introduces an easier method to add cores packages.

You can check in the boards tab if the ATtiny is listed.

Install on Arduino IDE 1.6, 1.5 and 1.0

Several versions of the cores are available.

Link for 1.6 Link for 1.0 Link for 1.5 and 1.0

In order to manually install a cores library, follow these steps:

  • Download the version of your code that suits your IDE/requirements.
  • Uncompress the zip file and locate the attiny folder.
  • Find the Arduino IDE sketchbook folder (the one that also contains the libraries).
  • Create a new subfolder called /hardware in the sketchbook folder in which you will copy the attiny.
  • Restart the IDE.

Once again, you can check in the boards tab if the ATtiny is listed (there should be a bunch of them).

3. Connect the Uno to the ATtiny

The circuit connects the Arduino ISP pins (MISO, MOSI, SCK, SS) to their ATtiny counterparts.

The connections go as follow:

Arduino ATtiny85
10 RESET
11 0
12 1
13 2
GND GND
5V Vin

4. Set-up the clock rate at 8Mhz

The clock rate of the ATtiny out of the factory is 1Mhz but the internal oscillator can go up to 8Mhz (you'll need to add a crystal for more).

  • Select the ATtiny85 board with a frequency of 8Mhz on the internal oscillator in the board tab.
  • Select Arduino as ISP in Tools->Programmer.
  • In the same Tools menu, click on Burn bootloader.

There you go. Your chip is now running 8 times faster!

4. Upload the famouse Blink sketch

It's always good to perform a very simple test. And what could be easier than blinking an LED?

  • Grap any LED in your parts bin and connect it to pin 4 on the ATtiny through a resistor in serie. Choose a common value between 270Ohms to 1k.
  • Open the Blink sketch found in Files->Examples->1.0 Basics
  • Change the LED pin number from 13 to 4
  • Watch amazed as the LED starts blinking