What you need:
- CR2032 battery. Get them at Digikey for about $0.25 each. I wouldn't trust the ebay ones.
- Diffused 5mm Slow or Fast Fade Flashing RGB LED from Adafruit. $4.95 / 10 pack ($0.50 each!)
- 330 ohm resistor.
- Rare earth magnet. I go to ebay for these. I used 10x1.5mm, but about any type should do..
- Soldering iron and solder.
- Hot glue gun.
Fast fade on the left, slow on the right.
Step 1: Resist!
The lower the LED voltage, the higher the current it will draw! I know you EEs are ready to hand out a dope-slap, but hey, there it is. When I tested a plain old yellow 2V LED with it was pulling more than 40 mA, way more than healthy! A higher voltage LED like blue or white would only pull 10 mA. Still, at 10mA, how long is a 225 mAH battery going to last? Yes, about a day. We still need a resistor.
- Wrap one end of the 330-ohm resistor around the LED's short lead, solder it and clip it.
Step 2: Rare Earth
- Place the magnet on the positive side of the battery and tack it in place with hot glue. Not too much now, or it will leave a gap, preventing the lead from making contact.
- Curl the end of the LED with the resistor attached. This will give you more area for the glue to hold it.
- Hold the battery in place, ensuring it lights, and solder the resistor side to the battery negative side. Make sure the LED stay lit until the glue hardens.
Step 3: Could We Be Done?
Remember, once the battery is dead, peel the LED off and reuse it while recycling the dead battery safely.
We did this for a library event craft project. See more of my projects at MakersBox.blogspot.com
Your challenge is to find a crafty project to encorporate a blinky in to. How about a card-stock lighthouse or a firefly? Send me a picture and I'll post it here!