I like the geeky stuff too, but fortunately there’s not much to it. Both the electromagnet and laser beam break sensor are on breakout boards. They already have pull-up resistors on the breakouts so no need to solder external resistors on a prototyping board to ensure there are no floating pins. I just hooked them up directly to Arduino with pre-crimped terminal wires and terminal housings from pololu (I taped the terminals so that they wont come apart):
https://www.pololu.com/category/39/cables-and-wire
so they won’t get loose at school.
Code were snippets from where I bought the breakout boards:
http://www.seeedstudio.com/wiki/Grove_-_Electromagnet
http://www.wvshare.com/downloads/accBoard/Sensor-Kits.7z
[Original trap concept]
The real geeky stuff was our initial concept for the trap. We were going to have 6 features on the trap:
a) Solenoid latch to hold a prison cage door in place (we switched to a barn house and electromagnet when we realized we didn’t have time to print everything on a weekend).
b) Light with a prism to create a rainbow road (getting the angle right and getting a good enough light source was a problem…a white led wont give you rainbow colors)
c) Use one RGB LED breakout board to cycle different through different RGB colors inside the cage or barn house.
d) Mount a microview OLED to with icons like a beer stein, gold coin, shamrock, and leprechaun hat to entice leprechaun to approach the trap.
e) Use Arduino’s tone generator to play Zelda’s Lullaby song to lure leprechaun.
f) Use laser beam break sensor or hall effect sensor to detect leprechaun in trap.
[Challenges]
1) Designing and prototyping mounts for each and 3D printing them will eat up too much time.
2) Running multiple Arduino sketches requires that I time-slice actions in milliseconds to get an equivalent of multithreading on all the different breakout boards attached to the sensor. Arduino runs on a blocking loop so I will need to specify a time range in milliseconds for laser detection, for the tone generator, and so on.
3) How much power do I need to run all devices? Hooking up the laser, rgb led, and electromagnet alone was enough to tax a 4xAA set of batteries. The laser wasn’t sensing correctly and it required time to troubleshoot the power requirements.
4) The OLED requires external pull-up resistors for the 2 I2C wires. I did start a prototyping board with a piezo speaker and pull-up resistors but decided to simplify things. We also needed to code all the icons or even replace them with just text.
5) We only have the weekend and Monday night to get everything completed.
[User Consideration]
1) My kid is in first grade. I won’t be there with him at school during his presentation. Using the trap should be as easy as possible and he should be able to fix things himself like replacing the battery and switching it on. A switch is better than telling him to unhook the battery or coding Arduino to sleep after a certain duration (he might get confused when it stops working). A switch is more intuitive and easy to instruct on usage.
2) Safety. I originally had the Arduino hooked up to an RC 7.4V lipo (continuous discharge of 17A) battery so that it can provide enough juice to all components as needed. Unexpected things can happen like accidental shorts. That much amps can cause a fire on an accidental short. I replaced the lipo battery with 4xAA batteries. It’ll heat up in cases of shorts but should not cause any fire.
