In this case, a picture is NOT
worth a thousand words. Your picture is almost worthless in understanding what your daughter has cobbled together. What @(*steve*)
requested was that you post a schematic
diagram, NOT a picture of a jumble of wires and barely visible, value unspecified, components on a breadboard. That picture is worse than a Fritzing
image, and those are pretty damn useless except for "monkey see, monkey do" activities.
If you really want our help here, please post a link to where you obtained
a simple metal detector circuit using an example from the internet
And if the link doesn't contain a schematic diagram, perhaps you can draw us up one by hand, photograph and post it? Or maybe your circuit is a variation on this one (copied from this blogspot post
: at first look I thought the OP was using bare copper wire. Typical newbie mistake. It is almost impossible to tell from the picture whether the wire, which appears to be stranded, is covered with a clear plastic insulation or not. The soldered connections to the breadboard wires also look a little hinky. But the worst thing is this a an oscillator running at about 10 MHz. The 2005 datasheet
from STMicroelectronics for this, now obsolete part, says "When using Litz wire instead of single wire, the parallel resistance of the coil becomes higher and value of R1 may be increased, resulting in better sensitivity."
There are several You Tube videos
demonstrating this circuit. It appears to have a very short, probably not a practical, detection range. Mainly useful as a proximity detector, although Hall-effect devices do a much better job if you don't mind having to use a small magnet as the proximity target.
Kaman Nuclear (now Kaman Precision Products
) used to make and sell a similar proximity detector, based on eddy-current induction in an aluminum (typically) target in the 1960s. It was a linear device that provided a precision analog output signal representing distance to the target.
The ST application notes indicate a ferrite pot-core was used as a coil-form to wind the coil for the TDA0161 in various sizes, but it doesn't indicate whether the ferrite was left in place after winding the coil. I doubt whether it was because that would increase the inductance a lot and concentrate the magnetic field to the nearby vicinity of the coil. Most of the videos I have seen use an air-core coil, which "feels" about right for a hundred or so turns about two or three inches in diameter to resonate at somewhere between one and ten megahertz. An oscilloscope would be a big help in getting this contraption to actually work. Stray capacitance plays a huge role with this type of circuit at these MW radio frequencies.