GPS Soil pH Mapping Rover using Arduino

Soil pH decides which nutrients a crop can actually absorb: below about 5.5, phosphorus and molybdenum lock up; above 7.5, iron and zinc become unavailable. Yet most small farms manage fertility with a single blanket fertilizer dose, because lab soil testing is slow, costs money per sample, and gives one number for a field that may vary widely across it. Precision agriculture fixes this with spatial soil maps, but commercial mapping rigs are far beyond a student or smallholder budget. A low-cost rover that drives to sampling points, dips a pH probe, and stamps each reading with GPS coordinates brings that idea within reach of a classroom: the hardware is an Arduino, a GPS module and a pH probe, and the output is a genuine geo-tagged dataset the student maps, analyzes and defends in the viva.

1. The pH probe is calibrated with pH 4.0 and 7.0 buffer solutions and conditioned per the included procedure before the survey.
2. The operator drives the rover to a sampling point using the Bluetooth remote and presses the sample button.
3. The Arduino holds the rover still, reads the analog pH probe after the configured settling delay, and averages several ADC samples.
4. The NEO-6M GPS NMEA sentences are parsed for latitude, longitude and fix quality.
5. Timestamp, coordinates and pH are written to the microSD CSV and shown on the LCD with the running point count.
6. After the survey, the CSV is copied to a PC and the Python script renders the color-coded pH map and KML overlay.

Tech stack:

• Arduino Uno (ATmega328P), firmware in Arduino IDE (C++)
• NEO-6M GPS module (UART, NMEA parsing)
• Analog soil pH probe with signal-conditioning board
• HC-05 Bluetooth module (serial SPP remote control)
• L298N dual H-bridge, 4WD robot chassis
• 16x2 I2C LCD, microSD card module (CSV logging)
• Python mapping script (matplotlib heatmap + KML export)

• [Geo-tagged pH logging] A NEO-6M GPS module records latitude and longitude with every reading; the Arduino appends timestamp, coordinates and pH as CSV rows on a microSD card.
• [Bluetooth remote drive] An HC-05 module gives serial remote control from any Bluetooth terminal app, with a typical open-air range of about 10 m (Class 2).
• [Buffer-calibrated pH sensing] An analog glass-electrode soil pH probe with a two-point buffer calibration (pH 4.0 and 7.0) procedure, probe conditioning and rinsing protocol included.
• [Onboard LCD readout] A 16x2 I2C LCD shows live pH, GPS fix status and the number of points logged, so surveys run without a laptop in the field.
• [Dwell-and-measure cycle] At each sampling point the rover halts, waits a configurable settling time (default ~45 s) for the probe to stabilize, logs the reading, then resumes — started by a button press or remote command.
• [pH heatmap mapping] A Python script converts the survey CSV into a color-coded scatter map (PNG) and a KML overlay for Google Earth, ready for the report.
• [Rechargeable field power] A 2S Li-ion pack with 5 V regulation powers the rover; expected field runtime is approximate and load-dependent.

• Assembled rover prototype (chassis, electronics, probe mount)
• Arduino firmware source code with comments
• Wiring diagram and full component list
• Buffer-calibration and field-survey procedure document
• Python mapping script (heatmap PNG + KML export)
• Project abstract PDF
• Project report (background, methodology, calibration procedure, sample survey results)
• PPT presentation and viva Q&A document

• GPS needs a clear view of the sky; the ~2.5 m CEP accuracy means closely spaced grid points blur together, and indoor demonstrations are not possible.
• The glass pH electrode is fragile, drifts, and needs two-point buffer calibration before each survey; it must be stored in KCl storage solution and rinsed between points.
• The probe needs 30–60 s of settling time per point, and dry or compacted soil must be wetted per the procedure — moisture differences shift readings.
• The rover is remote-controlled, not autonomous: mapping density and area are limited by the ~10 m Bluetooth range and the operator.
• The 4WD toy chassis can slip on loose tilled soil and cannot climb obstacles; the operator picks the sampling path.
• This is a small-scale demonstrator, not a replacement for laboratory soil analysis.