Got a bit of a surprise today when I looking in the inbox on lookout and there was a new challenge for using Wireless Power. Last Fridays rather left field thoughts about a tracker that uses BlueTooth and GPS and was charged by wireless power. The wireless power is cool as i can then pot the entire unit into a small block (as long as i have got the code right!). I had gone down the road of trying to layout a small spiral on a PCB and now i find that Wurth have coils and Element14 almost stock them... There is also the TI controller in consort with the coil. My original ideas were much simpler as i was going to use microcontroller in the base unit to drive the transmission coil and just simply rectify the receive side of things. I am NOT going to try and push 5W through the coil as the battery i plan to use, the Panasonic Lithium Vanadium Pent-oxide, can't be charged all that quickly anyway. I was also looking at some smarts of communicating over the power link via some sort of modulated m-sequence over the oscillator coil. The communication link from the charger to the unit is easy -- just do a phase flip every x cycles (10 to 20) to keep the signal a reasonably tight bandwidth for coil efficiency. For communicating back to the charger I was just going to modulate an extra resistive load so that the current draw in the charger by the coil would represent the signalling. It wouldn't be fast BUT you would get some sort of ability to throttle back when fully charged etc. I did something reasonably similar for a capacitively coupled signalling over power lines where i had a constrained number of conductors on a cable a few years ago. That used a dsPic30 and was able to punch through the noise on the cable pretty well...