Here are some pictures of the finished product. The circuit was simple enough for him to "design" it (with prompting and some good old Socratic method). He did the parts layout, I did most of the wiring. About half of the soldering joints were done by me, and the other half by a rising 8th grader who had never soldered before.
One unusual aspect to the circuit is that all of the ground pins of the LEDs are tied together, and that ground pin is connected to a single 100 ohm resistor which is then connected to the negative side of the coin battery. Normally, there should be a single 100 ohm resistor that independently connects each LED to the ground. This design saved on parts with the restriction that if multiple LEDs are turned on at the same time, they will appear dimmer than if only one is turned on.
Of course the resistor is probably the cheapest part in the entire project, but doing it this way also saved on the number of soldering joints needed to finish the project. In the end, I think the soldering is what takes the most time and is the most frustrating, so it's probably worth it for that.
All of the parts in this project are readily availble through multiple sources. All links/costs valid as of July 2013.
|5||generic led||thaishine||$3.51 for 30||nte30043||$1.51|
|1||100-220 ohm resistor (1/4-1/8 watt)||thaishine||$2.20 for 100||271-1108||$1.49 for 5|
|1||8 pin dip socket||thaishine||$3.17 for 40||276-1995||$0.99|
|1||circuit board||?||?||276-148||$2.49 for 2|
And I would be horribly negligent if I didn't mention the following mind blowing site: http://web.media.mit.edu/~plusea/ The really push the limits on what you can do with low tech electronics in non-standard ways.