At our local CoderDojo we wisely use the SparkFun Inventor's Kit. If you have not seen this I encourage you to take a look. Lots of nice components and a great guide (PDF). Many people undervalue the amount of work going into the guides for these kits. Good writing is hard to find, are rarely included in many lower-cost projects. However, since the cost of full Inventors Kit is still around $100 (without shipping) it is beyond the budget of most Maker events to let kids take these home. So here is my answer: lets find a way to use the low-cost Arduino Compatible Pro Mini combined with a short strip of addressable LEDs in a kit that we could sell for around $10.
Here is a picture of my initial design:
Arduino Moving Rainbow Kit
Now lets go through the components to verify that we can do this in the $10 price range.
Here is a place on eBay that sells the Pro Mini Arduino Compatible for around $2.00. Although I suspect that we could get them in quantity for less. Note that these do not have a USB port on them. More about that later.
Here is an addressable LED strip with 60 LEDs that we can find on eBay for around $17.00. You can cut these up into 6 strips of 10 LEDs each which gives you a price per kit of around $2.80. What is wonderful about these LED strips is that they only take two power pins and a single data pin to hook up! I use the standard WS2811B which you can program with many libraries. I have some sample code on github that uses the Adafruit NeoPixel libraries, however I have found other libraries work well also. Keeping wiring simple is important for kids that don't yet have the fine motor skills (and patience) to wire up complex projects.
Now the last two components are the mini soderless breadboad (around $.70 in quantity), a switch and a power source. In the kit in the photo above I am using a 3.7volt Lithium Poly battery taken from an old RC helicopter that no longer works. We could also use an external 3 AA or AAA battery holder for around $1.
I also added a power switch and a clear plastic polystyrene box I purchased at the Container Store, although a small plastic leftover box will also work well.
Arduino Pro Mini Rainbow Kit Parts List
- Arduino Compatible Pro Mini $2.00
- 10 element LED strip $2.70
- Solderless mini breadboard $0.80
- Battery holder $0.70
- Plastic Polystyrene Box $2.50
- Wire $.50
- On-off switch $1.00
I also suspect that if we purchase these in quantities of 20 or more the prices would come down a bit and we could get in under $10.
The biggest challenge is that each station must be equipped with a laptop with a FTDI basic breakout programmer with the Arduino software pre-loaded. The Arduino Uno (which runs about $25) does not need the FTDI programmer, but would be 10x more expensive for each Rainbow kit. Getting these setup and configured is not easy.
I should also acknowledge that when we purchase items off of eBay or other sources, we are not using the official mini supplied by the fine people at Arduino. However at over $20 these devices would not fit into our under $10 budget. I still think that for other projects we should encourage people to use original Arduino hardware since the costs go to promote further open Arduino projects and quality educational materials.
Let me know your thoughts on this. Getting high-quality clear plastic boxes that kids could take home, throw in their back and show their friends is still something I am working on. I found one source here that I might try but any suggestions you have would be great. I know other projects use simple baggies for their parts but these seem hard to use and show to others.
There are also other options is to provide a "night light" mode that you could plug into a wall outlet and not have to use batteries. I have seen 5v USB "wall warts" for under $1.
Although I know that this is a very small project to get kids started in Arduino, I think it might be the platform that other projects could be added. Creating a clock (12 LEDs required), putting sensors on to display temperature or adding accelerometers and magnetometers might be the next step for these kids. The key is that they could take them home and show their friends and that keeps them interested and motivate to continue their work.
I also want to thank Gerd Knops for helping me get started on using the LED strips. He is a brilliant engineer, a great friend and wonderful mentor to me. I hope that what I learn from Gerd I can use to get more kids interested in science, technology, engineering and math. We don't really have much time left to do this.