Mdx1

MDX-1

An open, simultaneous multi-frequency + pulse-induction metal detector — hardware, search coil and firmware.

MDX-1 is a from-scratch detector design: a KiCad schematic and 4-layer main board, a 2-layer user-interface board, a hand-wound search coil, portable C firmware with a host simulator and test bench, and iOS/Android companion apps. The receive and transmit engine is specified around a coherent, DSP-first architecture:

• Five simultaneous VLF frequencies — 5.12, 10.24, 15.36, 20.48 and 40.96 kHz (harmonics 1, 2, 3, 4, 8 of a 5.12 kHz fundamental) from a single optimised 3-level look-up-table waveform, so every line falls exactly on a DFT bin and demodulates with one coherent transform.
• Two 24-bit, 512 kSPS converters — one digitises the receive coil, the second digitises the transmit current for exact V_RX/I_TX normalisation. Fixed gain, no AGC or blanking.
• A 100 V bipolar pulse-induction mode on the same H-bridge, plus a hybrid mode that time-interleaves PI bursts between VLF periods.
• STM32H743 (Cortex-M7, 480 MHz) with single-crystal-coherent timing, a Bluetooth audio module, a Sharp memory LCD, GNSS find-logging and an IMU for swing-aware ground tracking.

Status: experimental, design stage

This is a paper design that has not been built or field-tested. The schematic is ERC-checked, the PCBs are placed and routed, the firmware core passes its host test bench, and the STM32 target layer is written against the CubeH7 HAL but has not run on hardware. Nothing here has been fabricated, assembled or measured. Component values, footprints and firmware behaviour may be wrong. Verify everything against the primary datasheets before ordering or building.

The transmit stage switches up to 100 V through an H-bridge into an inductive load. Treat it as a hazardous-voltage circuit: it can injure you and destroy parts if mis-built. Build and power it only if you are competent with high-voltage switching electronics.

Main board, populated (3D view). Per-layer plots for both boards are in hardware/mdx1/images/.

Layout

The toolchain

The KiCad schematic and boards are the source of truth — they are hand-placed and hand-routed. The remaining tools are read-only against the boards or operate on design inputs; none of them modify the .kicad_pcb / .kicad_sch files. (The original placement/schematic generators were removed to prevent accidental overwrites of the finished layout.)

To regenerate the fabrication package after any board change (from KiCad's bundled Python):

/Applications/KiCad/KiCad.app/Contents/Frameworks/Python.framework/Versions/Current/bin/python3 tools/fab_jlc.py

Firmware

cd firmware
make test        # build the portable core against the host simulator and run the test bench
make screens     # render the UI screens from the simulator

The core (firmware/core/) is target-independent C: DSP, detector logic, UI, phone link, audio. The simulator (firmware/sim/) provides a synthetic coil/target/ground model so the whole signal chain runs and is tested on a desktop. The STM32 layer (firmware/stm32/) maps the core onto the H743 peripherals.

Before fabricating

• Run DRC to clean and re-confirm the design rules for your fab.
• Get a live distributor quote against the current BOM (part availability changes).
• Re-verify every configuration strap and value against the primary datasheets in docs/datasheets/.

License

Copyright © 2026 Stephen Packer.

This project — hardware, search-coil design, firmware, apps and documentation — is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). See LICENSE for the full text.

In short, you are free to share and adapt the material for non-commercial purposes, as long as you give appropriate credit. Commercial use is not permitted without separate written permission from the copyright holder.

Note: CC licenses are not designed specifically for software. CC BY-NC 4.0 is applied here to express a single non-commercial intent across the whole project (hardware, firmware and docs together). For commercial licensing of any part, contact the author.

Disclaimer

Provided as-is, with no warranty. This is an unbuilt, untested hobby design involving hazardous voltages. You are responsible for verifying correctness and safety before building or powering anything. Comply with the radio-emissions and other regulations in your jurisdiction before operating a transmitter of any kind.