In order to improve my Bluetooth controlled induction hob (http://johannesc.github.io/induction-hob/) I need a better temperature sensor. Since there is a magnetic field - how hard can it be to harvest energy from that?
Today I took the time to program the ATTINY2313A that is the "brain" of my temperature sender circuit board. I used my Bus Pirate as a programmer together with avrdude and it programmed without any trouble. Getting the software to do what I want took another couple of minutes before I discovered that I soldered one LED backwards. After that the board now turns the LED on when pressing a button and off when releasing :)
A couple of weeks ago I used a grinder to make room for some insulated copper wire. Today I decided to measure how much voltage I get out from it.
Unfortunately almost no voltage at all were present. Instead I made a couple of loose coils and put on the surface and then I got some voltage. It seems like the magnetic field does not travel so long into the frying pan.
After some tests I found that 2 turns were enough to get a good voltage.
In above pictures I have measured the voltage with a 10x probe. The first picture is lowest level (U) and the next one is level 2 and the last maximum level (P). My induction hob has the following levels 0,U,1,2,3,4,5,6,7,8,9,P.
When it comes to current there seems to be plenty, short circuit them makes the warn.
The "tricky" parts here is that I need to "store" the energy for ~1.6s when using the lowest level (or perhaps it is enough to take a measurement and transmit it in 400ms) and that I need a compact circuit to convert an input voltage between 10-25v AC to 5v or 3.3v DC depending.
At some point I wanted to extract the thermistor from my induction cooker to the outside. It offers temperature regulation, but unfortunately the thermistor on the other side of the surface doesn't measure anything realistic.
But before I found good extension wires, I realized that the circuit that involves the thermistor is connected to mains, so having the thermistor flapping in the breeze with no good insulation is a really bad idea. So I stopped.