Circuit design/critique: metal detector (college)

Discussion in 'The Projects Forum' started by MrFancie, Mar 9, 2012.

  1. MrFancie

    Thread Starter New Member

    Mar 9, 2012
    Hi everyone!

    This is my first project that hasn't been a list of parts just handed to me by a teacher. They said come up with a project and build it yourself. Very open ended.

    -I found a metal detector schematic
    -Reverse engineered it into block diagrams
    -Researched each section
    -And finally came up with my own authentic schematic (I even chose parts based on local availability for the IC, diodes, and transistor)

    The device premise is that there is a local oscillator balanced to the tank/detector osc. They are fed into a mixer where the sum &difference are output. The sum is filtered along with any harmonics. Then difference is then amplified and output through a speaker. When metal passes the only inductor in the circuit, the detector osc changes it's frequency and the balance is thrown off creating an output noise.

    My problem is I'm not sure how to pick values for the resistors and capacitors.
    I'm also unsure what I should make the resonant frequency that they are balanced to.
    Finally, I'm unsure if the circuit I made is even plausable. Whether the voltage will go properly where I'm intending it to go.

    Can anyone critique it?
    Possibly teach me about value choosing, or share experience that may help?
    I feel over my head :(

    Thanks to all who reply!