Does it have to be induced across a gap? It should be easy to fit 2 or 3 insulated rings to the rotating shaft (for power in and data out) and fit 2 or 3 spring loaded contacts on a bracket somewhere. If noise is too great a problem when crossing the joints in the rings use the noise as a synchronisation signal for data transmissions. At 3500rpm you have 17ms per rev, more than enough time to send 5 bytes @ 2400 baud 8,N,0 each rev. Bye. -----Original Message----- From: Jinx [mailto:joecolquitt@CLEAR.NET.NZ] Sent: Tuesday, 29 May 2001 22:58 To: PICLIST@MITVMA.MIT.EDU Subject: [EE]: Inducing power Hi all, perhaps someone can help with a wee power problem. I've got a circuit board mounted on a motor shaft. The circuit is there to measure the movement of an escapement mechanism (kind of like a governor) as the shaft turns from 100 to 3500rpm. The circuit itself is not a problem, I've managed to attached a small slider pot to the escapement and it's measuring OK with an ADC. What I'd like to do is induce power to the circuit using some kind of magnet/coil system. I need around 15mA at 6VDC. A possibility is to use a 7-segment LED (synched with the rotation) to indicate the escapement movement, hence the power requirement. Using batteries is not really an option because of the duration of the measurements and particularly if the LED idea goes ahead. I've got plenty of envultured materials - strong HDD magnets and more scrap transformers (enamelled wire of all gauges and laminate cores) you can shake a stick at. I thought I may be able to attach a small DC motor to the main motor's shaft as a generator but that's proved too tricky because of space limitations. So, any ideas on the most efficient way to induce power into coils on the PCB from stator magnets ? TIA -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.