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.
Step 1: Parts
An ultrabright blue, blue-green or white LED*
A CR2032 battery
An ATtiny25/45/85 AVR microcontroller.
Optionally, a rare earth magnet.
You will also need these tools:
Soldering iron & solder
If you want to do this and don't want to bother programing the chip yourself, leave a message and I'll see if I can arrange a source of pre-programed chips.
Assuming that you need to program the ATtiny you will need:
Parts (unless you have a programing shield for ATTinys):
A DIP8 socket
6-pin 0.1" male header (or 4-pin if you use jumper leads below)
About 2x6 inches of essentially any insulated wire or 1-2 jumper leads (ideally two colours)
Or (alternative parts):
An Arduino (an ISP programmer would also work)
PC with Arduino IDE & Arduino Tiny cores (more on this later)
Hot glue or epoxy advisable
* You could use an Red, Orange, Yellow or Yellow-Green LED but you would need to use a resistor or you would risk a brown-out on the controller and will get a very short lifetime. This adds 30% to the parts count but almost nothing to the price. 300-500 Ohms is not a bad place to start if you go this route. Maybe a little less for Yellow-Green.