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Metal detector based on Raspberry pi Pico

Metal detector based on Raspberry pi Pico

 Pulse  induction metal  detection  relies  on the  fact  that  when metal  is  in  a changing  magnetic field,  eddy  currents  are  induced  in the  metal.  

These  eddy  currents  form  complete  circuits  which  are equivalent  to  electro-magnets  which  generate  their  own  magnetic  fields.  As  these  induced  magnetic fields fluctuate, they also induce current in the originating inductor (searching coil).

If the searching coilin this circuit is driven with a current pulse, when the pulse ends, current will continue to flow in the searcing coiland in this case the current will decay because there is a resistive load on the antenna. As the current decays, the magnetic field will also collapse.

The effect of externalmetal in the magnetic field of the searching coiland the resulting fields produced by induced eddy currents is to prolong the decay of the current in the searching coil. 

We can detect metal near the searcing coilby noticing when the decay period starts to extend and measuring voltage difference against normal decay. Principal  advantage  of  this  kind  of metal  detector  is  hardware  simplicity  and  simple  tuning operations. 

The sensitivity is also good. As drawback, is difficult to implement a method to discriminate metal type.

The analog part of the schematic is classic, is inspired by SPIRIT PI 2.0 ESP32 (N.E.C.O) schematicand often used bya lot of people who are manufacturing their own metal detectors.

But idea was to replace the digital part  (usualy ESP32, ATMega8 or Arduino Uno boards) with Raspberry Pi Pico based on RP2040 microcontroller.

some important features of the board:Form factor21 mm × 51 mmCPUDual-core Arm Cortex-M0+ @ 133MHzMemory264KB on-chip SRAM; 2MB on-board QSPI FlashInterfacing26 GPIO pins, including 3 analogue inputsPeripherals2 × UART, 2 × SPI controllers, 2 × I2C controllers, 16 × PWM channels, 1 × USB controller and PHY, with host and device support,8 × PIO state   machineInput power1.8–5.5V DCOperating temperature-20°C to +85°C.

for more find here with all docs,

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