Using an inductor to generate a magnetic field?

Discussion in 'The Projects Forum' started by dmonking, Mar 17, 2013.

  1. dmonking

    Thread Starter New Member

    Sep 27, 2012
    Hey guys,

    I'm working of a project for school that revolves around "sending and receiving" magnetic fields to operate a robot.

    Basically, I'm trying to transmit a magnetic field at a fixed frequency generated from an inductor to a receiver composed of two inductors, and a bunch of other components to measure/ modulate the amplitude. Inductors I'm using are all 1.16mH. I asked my professor what frequency wave I should try to generate, and he said 15kHz is what worked best for him.

    I figured I could just build an H-Bridge with PWM from a microcontroller to drive a series LC tank at resonance, but it doesn't seem to be working. The H-Bridge is outputting the correct square wave, but I'm not seeing a sine wave between the inductor. I know the H-Bridge is working right, because I tested it with a motor, and could make it rotate both ways at a variable speed. Also, it looks like my microcontroller (a variant of the intel 8051) can't PWM greater than 1000hz.


    Next, I googled a little bit, and came across this: More specifcally, I tried to build Figure 7 on page 6. The output wave of that circuit was a sine wave, but it was sort of disfigured at both ends.However, what was weird that instead of resonating at 14.8kHz like I hoped for, it did so at 128kHz. Also, changing the capacitor only slightly modified this value, even when replacing a 0.1uF one with a 100uF one. I wish I took a picture of the weird wave but I didn't, sorry.

    I then went on to testing a few more fruitless ideas/designs and googling for information for hours, but came up with nothing. And here I am asking for help. Do you folks know how I could build a magnetic transmitter or what I'm doing wrong?

    I know this is really wordy, and probably pretty hard to understand, given the nature of the project, so I'm really thankful if you got down this far!
  2. Mr.Gadget

    New Member

    Nov 25, 2012
    It looks like your driving either the transistors inside you isolators or your MOSFET's into saturation.