The ATtiny is in most ways a smaller version of the ATmega – the brain of an Arduino – and I will be attempting to program it using the Arduino for ISP. If you want to learn what ISP is you can briefly look at the wiki article or this finely detailed article which deals with programming ATMEL microcontrollers. But basically, ISP lets you program your chip when its already been placed into your circuit, which is why its known as In-System Programming (ISP).
To guide me through this process I will be using this tutorial by MIT Media Labs(which is somewhat outdated) and this more easily digestible guide on Instructables. As described on both website, I will be needing:
- Arduino Uno or Duemilanove (with an ATmega328)
- ATtiny85 (but you can also use an ATtiny45, ATtiny44, or ATtiny84)
- 10 uF Capacitor
- a breadboard
- jumper wires
- an LED
- a 220 Ohm resistor
First, we’ll need to install ATtiny support (also known as “cores”) into the Arduino IDE. I’m going to assume you already have the latest version of Arduino IDE (1.0.1 as of this posting), if not, you should go update it.
EDIT: While the above linked cores will work just fine with this tutorial, a much better version can be found here. The install process is much the same as below, simply copy and overwrite any files into the hardware folder.
- Locate your main Arduino folder
- In it should be a sub-folder called “hardware”
- Copy the ATtiny folder from inside the .zip to the hardware folder. You should end up with a folder structure something like Documents > Arduino > hardware > ATtiny that contains the file boards.txt and another folder called variants.
- Restart the Arduino development environment.
- If done correctly, you should see multiple ATtiny entries in the Tools > Board menu.
Next, we need to connect the Arduino to the ATtiny. It may be a good idea to make sure that the Arduino isn’t running anything. You can do this by uploading the “BareMinimum” sketch found under File > Examples > Basics. Then, connect the ATtiny to the Arduino in this way:
Here’s how my setup looked:
(NOTE: In the picture I reversed the GND and 5V on the Arduino. Don’t do that.)
The pin connections are:
- ATtiny Pin 2 to Arduino Pin 13 (or SCK of another programmer)
- ATtiny Pin 1 to Arduino Pin 12 (or MISO of another programmer)
- ATtiny Pin 0 to Arduino Pin 11 (or MOSI of another programmer)
- ATtiny Reset Pin to Arduino Pin 10 (or RESET of another programmer)
NOTE: Dont confuse the output pins (0 – 4) above with the actual IC pins (1 – 8), refer to the Fritzing diagram above and the diagram below to connect everything correctly. You can use the dot in the corner of the ATtiny to orient it properly. Double check everything before powering up unless you want to chance frying your ATtiny.
Configuring the Arduino to act as a serial programmer to program other chips is simple;
- Make sure the board being used is still the Arduino (you can see what board is being uploaded to at the bottom right of the Arduino IDE)
- Open the “ArduinoISP” sketch from the File > Examples menu.
- Upload the sketch to your Arduino.
- The Arduino should now be ready to work as an ISP.
NOTE: At this point the capacitor should NOT be used to connect ground and reset as it may prevent the sketch from being uploaded successfully.
Configuring the ATtiny to run at 8 MHz
Before we program the ATtiny with our first sketch, its a good idea to configure it to run at 8 MHz to it so that we can have our sketches run at a normal speed and use the SoftwareSerial library. You will only need to do this once for each microcontroller.
- Place the 10uF capacitor between ground and the Arduino reset pin. Be sure to connect the negative of the capacitor to ground.
- Select which board you are programming by going to Tools > Board. In my case I will be programming a ATtiny85 and running it at 8 MHz.
- Check to make sure the Arduino is serving as ISP by going to Tools > Programmer, and selecting “Arduino as ISP”.
- Finally, run the “Burn Bootloader” command from the Tools menu.
Programming the ATtiny
Now that we’ve gotten through all the steps of setting everything up, programming the ATtiny is easy! I’ll be uploading the Blink sketch in this example.
- Make sure that the ATtiny is still the board being uploaded to. (Check the bottom right corner of the Arduino IDE)
- Open the basic blink sketch.
- Remember to change the LED pin number from 13 to 0! (Check the ATtiny pin diagram above to see which pins you can use.)
- Finally, upload it as you would any other sketch.
It should give the following error twice:
“avrdude: please define PAGEL and BS2 signals in the configuration file for part ATtiny85“
Simply ignore the error message and you should be good to go.
If all went well, you should be able to get an LED to blink by connecting it from ATtiny “Pin 0″ (pin 5 of the IC) to ground with a resistor in series. Here’s how my ATtiny85 looks running the sketch:
Note how I don’t need to have it connected to the Arduino any more! All I’m doing is giving the ATtiny a 5 volt supply via a voltage regulator. But really, the ATtiny85-10PU can run just fine with 1.8 – 5.5 volts (depending on the frequency you run it at). I should also note that the maximum current rating per I/O pin is 40 mA, so don’t plan on powering anything too big with this IC.
If you’re looking for somewhere to buy ATtinys check out Mouser. Here is a through hole ATtiny85-20PU for $1.29, but you can also get the ATtiny85-20SU* for $0.83, which is in a very solderable SOIC package if you are interested in saving some money and getting into surface mount soldering. I would go so far as to suggest buying at least 5 of them, because once you start using them you will think of all kinds of tiny projects that you could put them in.
*(20PU means that it runs at maximum 20MHz, 2.7 – 5.5 volts. PU/SU is for package type.)
To make a dedicated ATtiny prototyping platform for the Arduino you can use a protoshield such as this and wire it up as shown here:
The space in the upper part of the mini-breadboard can be used for testing small circuits and debugging, though I would suggest using only Pin 3 and Pin 4 (left of the ATtiny in the image above) for this, as Pins 0 – 2 are used for programming. The bottom portion is used for programming status indicators, GREEN being all is well, YELLOW is programming in progress, and RED is error. Here is how it looks in real life: