- 1 US1881 Hall Effect Sensor (SparkFun part #COM-09312, or Digi-Key part #US1881EUA-ND)
- 1 big ass magnet (K&J Magnets part #BY0X02)
- 1 10mm Red LED (SparkFun part #COM-10632)
- 1 CR2032 coin cell (DigiKey part #P189-ND)
- 1 20mm coil cell holder (DigiKey part #103K-ND or part #3003K-ND)
- 1 56ohm resistor
- 1 10Kohm resistor (optional: the datasheet for the US1881 recommends this, but I didn’t end up using it. Worked fine without it. YMMV)
- 1 protoboard (about 1″ or 1.5″. E.g. Sparkfun PRT-08814)
- 1 poster with a robot image
1. Follow this schematic:
It’s pretty simple really, just 4 components. Note that with this setup, the LED will initially be ON. You’ll need to “turn it off” by holding the magnet up to it. The schematic could probably be modified to use a transistor like a 2N3904 to switch the LED the “right” way, but I was too lazy.
2. Print out a big poster with a robot image. Etsy has some great robot images available for sale. My wife found this lovely design for Retro Robots from cloudstreetlab. Then I uploaded the image to Mimeo.com and printed out a large 24” x 36” poster. (Disclaimer: I work for Mimeo.com). This was the perfect size to provide a nice big target for a 4 year old.
3. Put up the poster and place the Big Ass magnet behind the poster where the heart should be. Remember, the magnet in the parts list above is pretty damn strong (hence the “Big Ass” moniker). Do not place this near a CRT TV or hard drive. It will cause issues.
4. Put some double stick tape or a roll of masking tape on the back of the Robot Heart so that it will stick to the poster.
5. Blind-fold a kid, give them a Robot Heart, and see if they can pin it on the heart. The kid who is able to pin the heart and have the LED light up wins!
Here are pictures of the finished board, complete with crappy soldering.
You could get crafty can actually cut out the protoboards into heart shapes. Also, adding a few dummy capacitors, resistors, or extra wires might dress this up a bit, too. It’s a good chance to get creative.
Unfortunately, due to an ordering snafu, I didn’t end up getting enough parts for all the kids coming to the party. Therefore, we’ll probably have to save this for a future birthday. If anyone does use this, let me know how it went.