newbie experimenting with a diy detector

I'm new to metal detecting, and may be more interested in building a DIY detector than actually using it.  I'm trying to make a partially digital metal detector using a sound card and DSP to do the detection and discrimination, based loosely on the Neco Desarrollo Smart Hunter and TGSL projects but modified to have a slightly different coil and built using whatever I have lying around.  I hope to eventually use a raspberry pi zero w/ usb sound card or a smartphone to handle the calculations.  I've built a direct drive transmitter circuit from an old audio amplifier IC, and wound the TX coil after making a jig:





Working on making an ac coupled non inverting amplifier for the receiver now.  Hopefully this works, I don't really know what I'm doing but it's fun so far.  

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Thanks, after taking this picture I made a lot more constraining knots and dabbed on some varnish with a q-tip between the pegs.  After drying overnight the coil was super stiff (the thick wire helped too).  I made the second coil yesterday, giving it a few more wraps to increase the inductance (not really sure if it's necessary, but all the other DIY metal detectors I've seen do this).  I figured out how to measure the inductance with an oscilloscope too.  Now to build the receiver circuit. 

Interesting point about the wiggling unconstrained wires.  I'll apply varnish fully over both coils now that they're off the frame to reduce the problem.  When I'm done I'll make a wood coil housing and pot it with epoxy. 

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