Failed Detector

I designed this metal detector yesterday, and tested it. I labelled it a failure -- but here it is for interest -- it does detect metal. This is the first time one sees a digital-stream CCO metal detector. The two coils mostly overlap. The variable resistor adjusts input potential and frequency. But the whole thing needs jump-starting (twisting the variable resistor does it). And operation is iffy. I picked up a one-inch diameter coin at eight inches -- which is good -- but only once, and I couldn't repeat it.