EM ground conductivity sensor — bill of materials and coil design calculator
Transmitter
| Part | Part no. | Source | ~Price |
|---|---|---|---|
| AD9833 DDS module (GY-9833) Oscillator, 1 Hz–12.5 MHz, SPI | GY-9833 | Amazon | $3–5 |
| TIP31C NPN power transistor Tx coil driver, 3 A / 40 V | TIP31C | Digi-Key | $0.70 |
| 0.5 mm enamelled Cu wire (50 m) Tx coil winding | -- | Amazon | $8–12 |
| Polypropylene capacitor 1 µF (×2) Series resonant cap, Tx | ECW-F2105JB | Digi-Key | $1.20 ea |
| 10 Ω / 5 W current-sense resistor Tx current monitoring | -- | Digi-Key | $0.60 |
Receiver
| Part | Part no. | Source | ~Price |
|---|---|---|---|
| 0.2 mm enamelled Cu wire (100 m) Rx coil, higher-turn windings | -- | Amazon | $10–14 |
| Polypropylene cap (parallel resonance) Parallel tuning cap, Rx | ECW-F2105JB | Digi-Key | $1.20 |
| INA128P instrumentation amp Low-noise preamp, 1.3 MHz BW | INA128P | Digi-Key / LCSC | $11–19 |
| MCP6002 dual rail-to-rail op-amp Active bandpass filter | MCP6002-I/P | Digi-Key | $0.85 |
| Film resistors 1% (assorted) Filter & gain resistors | -- | Amazon kit | $6 (kit) |
Phase-sensitive detection & MCU
| Part | Part no. | Source | ~Price |
|---|---|---|---|
| AD630 synchronous demodulator Analog lock-in, IP/QP separation | AD630ANZ | Mouser / Analog | $12–18 |
| Raspberry Pi Pico 2 RP2350 MCU, ADC + USB | SC1632 | Adafruit / SparkFun | $5 |
| ADS1115 16-bit ADC module External precision ADC, I²C | ADS1115 | Amazon | $4–6 |
| ±15 V dual supply module For INA128 & AD630 | B0505S-1W | Amazon / LCSC | $3–5 |
Mechanical & ancillaries
| Part | Part no. | Source | ~Price |
|---|---|---|---|
| PVC conduit 20 mm dia. (2 m) Coil former, non-conductive boom | -- | Hardware store | $4–6 |
| Aluminium foil tape Coil electrostatic shield (gap!) | -- | Hardware store | $5 |
| Shielded cable 2-conductor (2 m) Coil-to-electronics connections | -- | Hardware store | $6–8 |
| Perfboard / proto PCB (×2) Signal processing boards | -- | Amazon | $5 |
| Misc: headers, decoupling caps, etc. 100 nF, 10 µF bypass caps | -- | Amazon | $5 |
Estimated total (one build)
$115–160
Prices as of April 2025. Note: current 10% US import tariff on electronics and 125% tariff on China-sourced goods may affect Amazon/LCSC prices. Buy INA128P and AD630 from US-stocked Digi-Key/Mouser to avoid tariff exposure.
Adjust parameters for either the Tx or Rx coil. The calculator solves inductance, wire length, and DC resistance.
15 cm
30
0.5 mm
Inductance
--µH
Wire length
--m
DC resistance
--Ω
Construction notes for this coil
Enter your measured coil inductance and desired operating frequency to find the resonant capacitor value. Use an LCR meter to measure L after winding.
5.0 kHz
200 µH
3000 µH
Tx — series resonance (maximise coil current)
Rx — parallel resonance (maximise voltage at input)
Q factor and bandwidth