Testing a transistor, relay, resistor combination to ensure long term success

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.

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