User:TheHypnotist
Projects
Mains timer hack
This project was meant to be a handy hack which would convert a timed outlet into being controllable from my laptop over bluetooth and then later added to a network of controllable/readable devices using cheap NRF24L01+ wireless modules.
Anyway, this project is now on hold as I let out the magic blue smoke and cant be bothered to fix it right now.
I killed it by causing a ground loop, If I had an isolating transformer it would have been alright but unfortunately connecting the oscilloscope to the microcontroller (msp430) ground pin caused it to pop! I'm sure the microcontroller is fine but not checked yet. Anyway, that resistor in the middle-ish right of the board is what popped and started to smolder. Funnily enough I watched it burn out before I bothered to unplug it lol. Too much fun watching the glow.
I had a firmware on the MSP430 (one of the microcontrollers you get with a TI Launchpad) which toggled a pin high and low every 1000ms so that I could test the relay was switching on and off. There was an issue, which was why I was probing it, the relay wasn't switching unless I touched the output of the microcontroller with the scope probe briefly - then it would switch on and off every second as expected until powering off the device. Weird. Not sure why it wasn't working to start with and shortly after discovering that I blew it up!
I had kind of expected it, but since this is my first time properly trying to do anything remotely near the mains voltage, I figured what the hell I would take a risk probing it since the scope can handle up to 400v max.
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<tweaker> I believe there is a problem with a floating pin on the input so it doesnt know which state its in <tweaker> so when you put the tip from the scope you make it so <tweaker> and then it starts sensing <tweaker> I suggest either a pullup resistor or a pull down
^ good point mate thanks for the advice.
