fh03 wrote:
Hello guys,

I am building an RF tag that will transmit some data using a
microcontroller and a 433 Mhz transmitter. But I do not want to place
any buttons on the device nor have it be on at all times. So I was
wondering is there a way to create a magnetic field at the source to
generate an induced current in this tag to perhaps flip a switch to
turn on the internal battery? And once the tag is out of the fields
range the switch will open again?

I know systems such as the Sunpass or other electronic toll payments
use something like this.

If anyone has any information on how this can be done, please help.

Thanks.


Some of the passive RFID stuff powers the card from the incoming carrier
wave -- but I have no direct experience with them. I don't know how
close you need to be other than having heard of them being used on
railroad cars passing a fixed installation.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com