I originally designed the tiny timer using an MJE3055 transistor. I did this because I had one laying around. Always a great excuse when hacking a project. For production purposes, that’s not usually the best choice. I decided that I would change over to one of my favorite transistors, the BC517. It’s a high amplification transistor with an Hfe rating of 30,000. This means that the signal amplification is 1:30,000. The first time I put a timer together with it I promptly fried it. That was unfortunate but a stark reminder to always check resistor values. So today I setup the breadboard to do some component validation. I wired a relay, BC517, and 1M ohm resistor. I then coupled it to an Arduino Uno. I don’t remember what sketch is on the Uno, but when I put a wire to pin 1 the relay started going off like a door bell. Good enough for testing. After an hour or two I’ll have accumulated enough cycles. It’s running at around 4 cycles a second. That yields 14,400 cycles an hour. I’ll let it go for a couple of hours. 28,800 cycles is a good break in test.
For your amusement I’ve attached a short video I took with my Nexus 4 Android phone.
