Sensing a microwave oven operation

I'm currently working on a fun little prank where the microwave will blast dub step after being turned on (OK, well a pair of speakers connected to an arduino with MP3 shield). I'm just missing the proper sensor to trigger the system.

I tried experimenting with the 30A non-invasive current sensor on Spark fun attached to one of the two internal wires of the power cord. The output was too small to read (after factoring in noise) as the current drawn by the microwave is 6A@120VAC. I've also tried using a kill-a-watt's opamp output as per ladyada's tweet-a-watt project but I have a slightly different model and forsome reason, the baseline output is 2.300 vvolts... rising to 2.306 with the microwave on. Also I ended up killing the whole unit somehow.

What other suggestions do you have? Does a microwave output a measurable magnetic field when its on?

What other suggestions do you have?

Mine turns the light on when it is running. Use a LDR.

The light comes on when the door is open too though

Why not use a master-slave power strip http://en.wikipedia.org/wiki/Power_strip to power the whole contraption? That is the microwave would be the master and the Arduino will be powered through a power supply in one of the slave sockets. Once the Arduino is powered up it can immediately go to play.

If you want the Arduino run all the time you could still use such a setup to push a signal to the Arduino by measuring if the power supply has power.

r34p3rex: The light comes on when the door is open too though

Yeah, but the other techniques for tapping into the magnetron power supply or picking up the presence of microwave radiation are difficult and/or dangerous. Powering an MP3 player from the supply to a light bulb via a 'door closed' switch seems trivial in comparison.

Have you tried simply placing your arduino beside the microwave. There may be enough leakage to "excite" it. Yeh I know they are not supposed to leak but who knows.