are great. They have a minimal parts count - 2 or 3 depending on whether you use a magnet - and produce a great effect. They are very cheap and easy but not highly efficient:
1) They are on all the time, so on average they waste half of their energy shining during the day.
2) A continuous light is not as visible as a flashing light. An interesting flash-pattern adds to the intrigue and can even convey information.
3) Their Duty cycle is too high - a duty cycle of 10-20% is more than sufficient to be both visible and much more efficient.
This is the first of what I hope to be 2-3 versions of microcontroller projects designed to be so cheap that they can be used as throwies. The plan is to make them more efficient and use that gain to provide a more exciting effect.
This is the "basic" version - it requires only one additional part, three blobs of solder and a few snips. And by magic* it can address all of the issues above. It's programmable using the Arduino IDE, hence "Throwduino".
On a per-hour basis it should even work out cheaper than a normal throwie. The cost analysis is in step 5.
Edit - Morse Code sketch now available - see last step.
- Now you can throw your own message of choice!
* not actually magic - see step 6.