August 25th, 2012 at 10:04 pm (Electronics)
As part of Kids Building Things, we’re hoping to offer kids a basic electronics workshop. Our current plan is to show them how to make Digital Dominoes, which are about the size of an analog domino but, instead of physically toppling, they propagate using LEDs. The first step was for me to give the project a test-run to see how difficult it is and how long it might take.
At right you can see the parts (click to enlarge) that come in a kit of four ($20). (If you look closely, you’ll note that my kit is missing one red LED, so I’ll need to swap in from my own supplies to make all four.)
I carefully inventoried the kit and read through the assembly instructions. Then it was time to plug in the soldering iron and get started! Below you can see the empty board.
Below is the back of the board, after I soldered all 40 joints. The first tricky bit for me was the NPN transistor, whose three joints (the triangle cluster at top) were so close together that I accidentally soldered all three together. This was quickly solved with the solder sucker and re-soldering them separately. The other tricky bit was that due to a “bug” in the board, you have to patch in a connection between two pins from separate components by bending the soldered leg of one onto pin 2 of the IC. Soldering the leg to the already-soldered pin seemed to suck the solder up out of that joint, and I worried that I’d lost the connection. I used my multimeter to check connectivity, and happily all was well. I trimmed the extra leg bit after this image was taken.
And below is the final product! (I manually triggered one for the photo — they don’t actually interact in this configuration.) The black photoresistor at left receives light, turns on the red LED, and also activates the clear IR LED at right, sending out a signal for the next digital domino in a chain.
It took me 70 minutes to make the first one, going carefully, and only 25 minutes to make the second one. Excellent soldering practice! I can’t wait to make some more and play with them — and then teach kids how to make their own!