DIY DD metal detector 2 - coin at 35cm, audio indicator, PCB

Some improvements to my sensitive DIY metal detector with a Double D (DD, 2D) balanced coil (about 15 cm / 6 inch diameter). Now it detects a small aluminium coin (18 mm diameter) at 35 cm distance and a small iron can at 70 - 80 cm distance. It has an audible indicator. Its pitch tells the signal strength. I'm moving it from a breadboard to a prototyping circuit board. It runs roughly at 11 - 12 kHz. Using a resonant capacitor with a lower dissipation factor (tan delta) in the transmitter reduced the power consumption. I also tried to fine balance the detector coils using potentiometers instead of physically moving them.

The first episode:
   • DIY DD metal detector 1 - first success  

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