[Noisebridge-discuss] Long-lived, battery-powered AVRs

[Jake]

Yes, you can bias a FET so that it's ready to turn on, and activate it 
with a coil which is energized by a moving magnet.  If you connect the 
coil through a diode to the gate of the FET, and put a capacitor on the 
FET gate, it will activate the FET for a period of time...

and then you can use the FET to turn on a radio transmitter, something 
REALLY simple, like 2 pieces, and then do the hard work on the other end 
where you have a radio reciever listening for the signal.

no microcontroller needed, zero power consumption when it's off.

and no coding!

everybody better brush up on your analog electronics skills because after 
the crapocalypse there's going to be no more sparkfun, and you'll have to 
build everything with the junk on the shelves and the rails and rails of 
analog and digital ICs that miloh and I catalogued and entered into this 
google doc:

https://docs.google.com/spreadsheet/ccc?key=0Asn-w52SL9z8dHhWLVlOQmkxLUk1YkdIbU1FWThqOHc#gid=1

-jake

Jof wrote:

That's more or less perfect for an application like this, though I
think it may not be a good contender, physically. Since this is to
detect a gate swinging open and shut, we were thinking of placing a
small coil-based sensor on the frame and a neodymium magnet on the
swinging gate.

Thank you everyone for some excellent suggestions. Sleeping the AVR
seems like the way to go, but waking it back up will be the trick.
Since I hope to use the small charge that will build as the magnet
passes over the coil, I was hoping to flip a small transistor. The
only problem I'm having is finding something that will trip with just
the slightest charge.
Would it be crazy to try and bias the gate of a small MOSFET so that
it's nearly triggered?

--j