SPH01-MS Soil pH and Temperature Mesh Node

1. Product Overview

SPH01-MS is a solar-powered Dragino Mesh Node for monitoring soil pH and soil temperature. It combines an IP68 buried soil probe with LoRa Mesh communication, allowing measurements to reach a Mesh gateway directly or through other Mesh Nodes when the gateway is outside the node's direct radio path.

The probe uses a solid AgCl reference electrode and a pure-metal pH-sensitive electrode. It includes internal temperature compensation to improve pH stability within its specified compensation range and is designed for long-term soil monitoring.

Soil pH measurements depend strongly on installation conditions, soil moisture, electrode condition, and stabilization time. The probe must be prepared, inserted, and maintained correctly to obtain representative results.

2. Applications

• Soil acidity and alkalinity monitoring in fields, greenhouses, nurseries, orchards, and landscaping projects.
• Long-term root-zone pH and temperature monitoring.
• Observation of soil-condition changes related to irrigation, fertilization, amendments, and seasonal variation.
• Comparison of pH conditions between different plots or treatment areas.
• Remote agricultural sites requiring solar power and multi-hop wireless coverage.

3. Main Features

• Measures soil pH and soil temperature with one integrated probe.
• 0.01 pH resolution within the specified product measurement range.
• Internal temperature compensation for the pH measurement.
• Solid AgCl reference electrode and pure-metal pH-sensitive electrode.
• IP68 probe suitable for buried or immersed measurement.
• LoRa Mesh communication with multi-hop relaying between nodes.
• S-type outdoor enclosure, solar panel, and 3000 mAh rechargeable lithium battery.
• Scheduled measurement and low-power operation.
• User calibration support at pH 4.00, pH 6.86, and pH 9.18.
• Firmware upgrade support through USB serial or PC BLE.

4. Enclosure and Probe Reference

For product photos, solar installation reference, enclosure dimensions, and probe appearance, refer to the solar-powered version on the SPH01-LB/LS product page.

The wireless and network behavior of SPH01-MS is based on Dragino Mesh rather than LoRaWAN. LoRaWAN-specific activation, payload, downlink, datalog, and server instructions from the SPH01-LB/LS page do not apply directly to SPH01-MS.

5. Technical Specifications

5.1 Main Unit

Item	Specification
MCU	STM32WLE5, 48 MHz ARM Cortex-M4
Flash	256 KB
RAM	64 KB
Radio	STM32WLE5 integrated sub-GHz LoRa radio
Power supply	Solar panel + 3000 mAh rechargeable lithium battery
Main board operating voltage	Approximately 2.5 V - 3.6 V
Main board operating temperature	-40 °C - 85 °C; battery operating temperature is subject to the battery specification
Local interfaces	3.3 V UART, BLE
Antenna	Sub-GHz LoRa antenna matching the shipping Region

5.2 Soil pH Probe

Item	Specification
Probe operating voltage	5 V - 24 V
Current while powered	Measurement peak less than 50 mA; average less than 2 mA
Communication	RS-485 / Modbus RTU
Factory communication settings	Station address 254; 9600, no parity, 8 data bits, 1 stop bit
pH response time	2 - 15 seconds, adaptive
pH stabilization time	Approximately 30 minutes - 24 hours, depending on probe condition and installation
Temperature stabilization time	Less than 5 minutes
Protection rating	IP68
Probe operating temperature	-10 °C - 70 °C
Cable length	Standard 3.5 m

5.3 Measurement Performance

Parameter	Range	Resolution	Accuracy	Additional information
Soil pH	3 - 10 pH	0.01 pH	Less than ±2 % under the specified conditions	Internal temperature compensation from 0 °C - 50 °C; frozen soil can reduce accuracy
Soil temperature	-40 °C - 85 °C	0.1 °C	Less than ±0.5 °C from -10 °C - 40 °C; less than ±0.8 °C outside this range	Measured by the temperature channel inside the probe

5.4 Probe Wiring Reference

The standard five-core probe cable uses the following wire definition:

Wire color	Function
Red	Power positive
Black	Power ground
Green	RS485-A+
Yellow	RS485-B-
White	SET terminal

The SET terminal selects the probe operating mode:

• Acquisition mode: connect SET to power ground.
• Setting mode: connect SET to power positive.

Normal SPH01-MS measurement uses acquisition mode. Setting mode is used only when changing the probe's internal communication parameters or performing direct probe calibration.

6. Understanding Soil pH and Temperature

Soil pH describes how acidic or alkaline the measured soil condition is.

pH condition	General meaning
Below 7	Acidic
Around 7	Neutral
Above 7	Alkaline

These categories are general references. Suitable pH targets depend on the crop, soil type, nutrient-management plan, and local agronomic practice.

The pH and temperature readings should be interpreted together. The probe applies internal temperature compensation within its specified range, but frozen soil, poor electrode contact, low moisture, contamination, and insufficient stabilization can still affect the result.

The electronic response time and the field stabilization time are not the same:

• The probe can produce a Modbus response within seconds.
• A newly installed, recently cleaned, or long-stored pH electrode can require much longer before the reading represents a stable soil condition.
• For permanent monitoring, evaluate trends only after the probe has stabilized at the installation point.

7. Probe Preparation and Installation

The pH-sensitive electrode and the reference electrode are mechanically fragile. Do not hammer, bend, twist, shake, or force the probe against stones or other hard objects.

7.1 Before First Use or After Storage

A probe that is new, recently cleaned, or has remained unused for more than approximately seven days should be activated before measurement.

Use one of these preparation methods:

1. Soak the sensing part in pure water for approximately 24 hours.
2. Pre-bury the probe in moist soil for at least 24 hours.

Keep the reference electrode moist when the probe is not in use.

7.2 Selecting the Measurement Point

Choose a location that represents the soil area being monitored. Avoid stones, buried metal, large roots, fertilizer deposits, drainage channels, and irrigation outlets unless that specific condition is the intended subject of the measurement.

For comparison between sites, use the same preparation, depth, moisture condition, and installation method. Differences in soil moisture and contact can otherwise dominate the pH comparison.

7.3 Temporary Measurement

For a quick or temporary measurement:

Open the soil to the target depth
            ↓
Remove stones and hard objects
            ↓
Moisten the measurement point with pure water,
purified water, or rainwater until the soil is muddy
            ↓
Insert the probe slowly without shaking or forcing it
            ↓
Pack soil around the probe body
            ↓
Wait for the reading to stabilize

Do not use excessive force. The metal pH electrode and the reference electrode can be damaged by impact or sideways movement.

7.4 Permanent Buried Measurement

For long-term monitoring:

Dig an access hole to the required depth
            ↓
Prepare a moist, stone-free measurement point
            ↓
Place the probe carefully at the bottom of the hole
            ↓
Fill and compact the surrounding soil
            ↓
Route the cable without tension or sharp bends
            ↓
Allow the probe to stabilize before defining baseline values

Install the enclosure above ground with the cable outlet facing downward. Provide a drip loop so water does not run toward the enclosure connection.

7.5 Installation Check

After installation, confirm that the node obtains plausible pH and temperature readings.

A fixed, extreme, or unstable pH value can indicate:

• insufficient probe activation;
• poor soil contact;
• soil that is too dry;
• stones or air gaps around the electrodes;
• electrode contamination;
• damaged probe elements;
• insufficient stabilization time;
• a probe connection or communication problem.

8. Data on the Mesh Gateway

Once the production Mesh Business Data payload and gateway decoder are enabled, the Mesh gateway is expected to present:

• Soil pH.
• Soil temperature in °C.
• Battery level or battery status.
• Device online status and data update time.

The exact field names, payload format, and gateway layout must be verified against the completed SPH01-MS production firmware. Do not reuse the 11-byte LoRaWAN payload from SPH01-LB/LS as the Mesh payload unless the Mesh protocol specification explicitly defines it.

9. Normal Operation

The intended production cycle for SPH01-MS is:

Wake up -> Power and read the pH probe -> Validate the measurement
        -> Send the current values to the Mesh gateway -> Enter low-power sleep

The probe may respond within seconds, but a valid communication response does not guarantee that the soil pH has reached field equilibrium. Recently installed or maintained probes can require additional stabilization time.

The final scheduled Mesh reporting and manual-report behavior must be confirmed against the completed production firmware.

10. Quick Start

10.1 Installation and First Measurement

1. Confirm that the product label shows SPH01-MS and that the antenna Region matches the deployment location.
2. Install the LoRa antenna before powering on the node, then place the solar panel where it receives stable, unobstructed sunlight.
3. Check the probe and cable for transport damage.
4. Activate the probe if it is new, recently cleaned, or has remained unused for more than seven days.
5. Before burial, power the node and confirm that the firmware can read pH and soil temperature from the probe.
6. Select the measurement point and prepare moist, stone-free soil.
7. Insert or bury the probe without forcing or shaking it.
8. Secure the enclosure above ground, keep the cable outlet facing downward, and protect the cable from pulling, crushing, and sharp bends.
9. Allow sufficient stabilization time before treating the first reading as a site baseline.
10. After Mesh reporting is implemented, verify that pH, soil temperature, and node status appear correctly on the Mesh gateway.

10.2 Initial Enrollment

For complete Mesh enrollment instructions, see Quick start — 2. First network test.

11. Power Consumption and Solar Power

Battery performance depends on the reporting interval, Mesh coverage, relay conditions, sunlight, solar-panel orientation, ambient temperature, probe power-up duration, and battery condition.

Short reporting intervals increase both radio activity and the number of probe power-up cycles. The pH probe can require a longer active period than faster environmental sensors, so the production reporting policy should balance response time, stabilization requirements, and available solar energy.

Install the solar panel for the site's worst seasonal sunlight conditions, not only for the conditions present during commissioning. Keep the panel free of dust, leaves, and shading.

12. Use and Maintenance

Inspect the installation periodically and after field work, irrigation-system changes, or soil excavation near the probe.

• Keep the solar panel clean and unobstructed.
• Check the antenna, enclosure mounting, waterproof connectors, cable, and drip loop.
• Keep the reference electrode moist when the probe is not in use.
• Do not allow the sensing electrodes to contact oil or greasy substances.
• Do not pull the probe by its cable.
• Loosen the surrounding soil before removing a buried probe.
• Protect both electrodes from impact, bending, and sideways force.
• After approximately 3 - 6 months of long-term burial, inspect and clean the electrode if the reading becomes slow or unstable.
• The metal electrode can be cleaned carefully with fine-grade sandpaper or soaked briefly in 5 % hydrochloric acid until the metal surface becomes bright again, then rinsed thoroughly with purified water.
• After cleaning, reactivate the probe and allow it to stabilize before comparing new readings with historical data.

Use appropriate protective equipment and local chemical-handling procedures when working with hydrochloric acid.

13. Calibration

The probe supports user calibration using these reference solutions:

• pH 4.00
• pH 6.86
• pH 9.18

It also supports restoration of the probe's factory calibration.

Before calibration:

1. Clean the electrodes.
2. Place the probe in the selected reference solution.
3. Wait until the value is stable. A newly cleaned electrode can require up to 24 hours.
4. Calibrate only with one of the supported reference values.

The probe-level calibration is performed in setting mode through its RS-485 interface. The user-facing calibration workflow for SPH01-MS—for example through a Mesh command, local service tool, or maintenance procedure—must be confirmed from the production firmware before publication.

Do not copy the LoRaWAN AT commands or downlink commands from SPH01-LB/LS into the Mesh documentation unless equivalent Mesh commands are implemented and verified.

14. Troubleshooting

Issue	Check and corrective action
The Mesh gateway cannot find the node	Confirm the Region, antenna installation, gateway status, battery level, enrollment state, and node wake state
The node is active but no pH or temperature reading is available	Check probe power, cable connection, RS485 communication, SET operating mode, and the required probe warm-up time
The pH value remains at zero or another startup value	Allow additional warm-up time and verify that the probe is in acquisition mode and returning a complete valid measurement
The pH value is fixed or changes very slowly	Check probe activation, soil moisture, electrode cleanliness, installation contact, and stabilization time
The pH value is unstable	Check for dry soil, air gaps, loose contact, nearby fertilizer concentration, damaged electrodes, cable movement, or insufficient stabilization
The reading differs from a handheld meter	Compare both instruments in the same prepared soil volume and at the same depth; allow both instruments to stabilize and confirm that the reference meter is calibrated
Soil temperature does not represent the target depth	Confirm that the probe is installed at the intended depth and is not influenced by direct sunlight or surface heating
Communication fails after changing probe parameters	Return SET to acquisition mode and confirm the configured station address, baud rate, parity, and stop-bit settings
The probe was stored dry or unused for a long period	Soak it in pure water for approximately 24 hours or pre-bury it in moist soil before evaluating accuracy
Values become unreliable after months of burial	Inspect and clean the electrodes, rinse with purified water, reactivate the probe, and allow it to stabilize again
Battery level continues to fall	Check sunlight, panel cleanliness, cable connection, reporting interval, Mesh coverage, probe active time, and ambient temperature
Soil values disappear after a firmware upgrade	Confirm that the installed firmware matches SPH01-MS and the shipping Region, then verify probe acquisition before testing Mesh reporting