Rocky Mountain College * Department of Computer Science * 406 208 3193 * turn on javascript to see my email

Blinky lights badge

I've wanted to try and use the Arduino-family of products to try and get middle-school students interested in computers. While I've seen a number of "blinky lights badge" kits at different places, the goal of this project was to 1) design something that could be programmed like an Arduino, 2) could be made from scratch so that at the end of the project the student could walk away with something in their hands that they made and worked, 3) had a much lower cost than the kits I've seen online. This project shows one such result. The only chip is an Atmel attiny85 which currently is available for a single unit cost of $1.29. It can be programmed using the Arduino programming environment following the instructions here. Additionally, we used an ordinary Arduino board as a programmer, as described here.

Here are some pictures of the finished product. The circuit was simple enough for him to "design" it (with prompting and some good old Socratic method). He did the parts layout, I did most of the wiring. About half of the soldering joints were done by me, and the other half by a rising 8th grader who had never soldered before.

One unusual aspect to the circuit is that all of the ground pins of the LEDs are tied together, and that ground pin is connected to a single 100 ohm resistor which is then connected to the negative side of the coin battery. Normally, there should be a single 100 ohm resistor that independently connects each LED to the ground. This design saved on parts with the restriction that if multiple LEDs are turned on at the same time, they will appear dimmer than if only one is turned on.

Of course the resistor is probably the cheapest part in the entire project, but doing it this way also saved on the number of soldering joints needed to finish the project. In the end, I think the soldering is what takes the most time and is the most frustrating, so it's probably worth it for that.


To see the original, download Fritzing and open up The fritzing file. If you'd prefer to not use fritzing, here is the breadboard layout and schematic.

Parts list

All of the parts in this project are readily availble through multiple sources. All links/costs valid as of July 2013.

# neededNameSupplierCostRadioShackRSCost
1 attiny85 digikey $1.29 n/a n/a
5 generic led thaishine $3.51 for 30 nte30043 $1.51
1 100-220 ohm resistor (1/4-1/8 watt) thaishine $2.20 for 100 271-1108 $1.49 for 5
1 cr2032 battery dipmicro $0.47 23-802 $5.99
1 cr2032 holder dipmicro $0.30 270-009 $1.49
1 8 pin dip socket thaishine $3.17 for 40 276-1995 $0.99
1 circuit board ? ? 276-148 $2.49 for 2


And I would be horribly negligent if I didn't mention the following mind blowing site: The really push the limits on what you can do with low tech electronics in non-standard ways.

You know we're constantly taking. We don't make most of the food we eat, we don't grow it, anyway. We wear clothes other people make, we speak a language other people developed, we use a mathematics other people evolved and spent their lives building. I mean we're constantly taking things. It's a wonderful ecstatic feeling to create something and put it into the pool of human experience and knowledge. -- Steve Jobs, Rolling Stone, November 1983.