Programming an ATTiny85 with an Arduino

image credits

A microcontroller (MCU for microcontroller unit) is a small computer on a single metal-oxide-semiconductor (MOS) integrated circuit chip. – Wikipedia: Microcontroller

As a farewell gift for a colleague who is also a fireman 👨‍🚒, I thought of the following:

  • I take a coloring book with a firefighter. In former times Grisu der kleine Drache (Grisu the little dragon) was popular, today it is Sam der Feuerwehrmann (Fireman Sam).
  • The book should show a fire truck with blue lights.
  • I replace the blue lights with blue LEDs.
  • To make it blink, I could use two transistors, NE555 or simply an ATTiny85.

The ATTiny85 is a MCU similar to an Arduino, but a bit smaller, with less IO pins and cheaper. It can be programmed, but not as easy as an Arduino, which you just connect to a computer with a USB cable.


The ATTiny85 has 8 pins in total. Two of them are needed for the power supply. That leaves 4 to 5 pins which I can use as output or input. I only need two pins to connect the LEDs and one pin to switch between different flashing modes. I use two wires as a switch and when you touch both the ATTiny85 reacts. I leave the input pin open and if it is more than 1 second HIGH I switch to the next mode.

ATTiny85 schem

Programming ATTiny85

It’s not the first time that I program an ATTiny85 and there are also different guides on the internet: Programming ATtiny85 with Arduino Uno

What is important?

  • proper wiring
  • Capacitor
    • observe the polarity
    • do not use it until the Arduino has been programmed as ISP
  • the programme

The following picture shows the setup for programming the ATTiny85: Programming an ATTiny85 - Setup

ATTiny85 programmed and wired for blinking: Programming an ATTiny85 - Blink

Flash modes

As you can see in the source code I have the following 5 flashing modes:

  • both LEDs blink at the same time
  • LEDs flash alternately
  • LEDs only light
  • LEDs are off
  • LEDs flash S.O.S.


After the ATTiny85 was programmed, I tested it first of course. For this purpose I built the circuit which I also installed in the book.

ATTiny85 blinking

I put the LEDs through the paper and bent the feet, with the ATTiny85 too. Then I soldered everything with the resistor, added the USB cable and tested it. The USB cable is only for power supply. There are also examples to control V-USB with ATtiny45 / ATtiny85 without a crystal. This can be used for example to make the LEDs of the fire engine blink when a tweet with the text “fire” is received.

All electronic parts soldered: ATTiny85 soldered

The front of the coloring book with the blue LEDs and ATTiny85: ATTiny85 coloring book

The mode selector at the wiper: ATTiny85 mode selector


A simple gift for less than 10 Euros and something to tinker. And the best thing is that many colleagues have perpetuated themselves in the coloring book.