seascan

Oh wow.  It will take me a little bit to digest this but, at first glance this does look like the answer!

As for the coils, I am planning on  two separate coils.  One to transmit and one to receive.  Can two SPI channels be opened simultaneously?   I was thinking to use one for the Transmit and One for the Receiver and then compare them to find the phase shift.

Okay...  let me ask about part 2 of all this:

IF a PWM wave of say 25KHz was driving the transmitter coil, is an ND2 fast enough to read say 8 points within the response.  So, the period is 40us.  To read 8 points would be a sample every 5us.  Can the Netduino reliably do this?  Based on this post  it looks doable.  Does anyone have any experience with high speed ADC with the Netduino?

I agree with the DSP approach.  PIC makes one that is somewhat user friendly but, that means learning WAY more than I intended... oh well, part of the fun I guess.

I have read that some detectors do use a square wave instead of a sine wave...  I am not sure if this is accurate information or not.  If it is then I was thinking that if I could use the PWM output coupled to SOMETHING to drive the AC wave then I could use two inputs to measure the phase shift.  One would read the PWM pulse and one the return signal.  Then measure the time delay between them.  Since they are both digital waveforms, I figure this would be a lot easier than trying to do the same with analog waves.

Thanks, Hazibal.  That's definitely an option.  

But, my goal is to see how much I can do with the ND... I'm not so much about the end result as how to get there!

Hi Mario!  Thank you for the reply.

Sorry... I knew I was struggling trying to describe my intentions.

My end goal is to try and make a metal detector... I figured this would be a fun project to help me (and anyone else interested) learn some fundamental concepts of Transmitters/Receivers!

I would like to see if the ND could be used to generate a signal then read the response amplitude and phase shift from a returned signal.

My starting point is the transmitter.  I was thinking of trying to use a PWM output and SOMEHOW converting this to an AC square wave (instead of 0-3.3V, perhaps convert this to +-12V or even +-5V.  Do you know of any devices that can assist in doing this?

Thank you!