Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Mag induction to power IR transmitter pulse

  1. Feb 26, 2005 #1
    I'm trying to design a simple circuit that will enable a magnet passing by an induction coil to send an IR pulse to a simple receiver plugged into a Linux box. This will be used to measure the speed of a turning wheel without having to worry about batteries or a power block of any sort. Any ideas?

    I have the design of a simple 555-based transmitter and a simple 38KHz receiver, all using parts from Radio Shack. My concern is powering up the capacitor and triggering the pulse with magnetic induction from a magnet attached to the wheel. Very much like a bicycle speedometer, where the magnet passes a reed switch to close a circuit, I want the magnet to pass by an induction coil to transmit an IR pulse.
  2. jcsd
  3. Feb 27, 2005 #2


    User Avatar
    Science Advisor
    Homework Helper

    What you seem to be talking about at this point is designing a generator.
    Probably doable if the wheel has a useful minimum/maximum rotation rate.

    Very difficult if the wheel is going to turn slowly as the power will be limited.
    Also difficult if the wheel turns fast, because there will not be enough time to transmit a complete data word before the next one comes due.

    First the pulse will have to store enough energy in a capacitor to run your transmitter circuit long enough to transmit the data pulse.
    You will also need some sort of voltage regulator or switching power supply circuit to get the voltage correct for the transmitter circuit.

    It will be a lot simpler to use a battery or power the circuit from whatever power source is turning the wheel directly, rather than building what is effectively a brake that will try to stop the wheel.

    You could also try powering the led directly from the coil, but that could lead to issues with other IR sources in the room.
    This is why remote controls use a 38Khz modulated carrier with several repetitions of the data word.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook