SPH01-MS Soil pH and Temperature Mesh Node

1. Introduction

1.1 What is the Dragino Mesh Soil pH Sensor?

SPH01-MS is a Dragino Mesh Node for monitoring soil pH and soil temperature. It combines an IP68 buried soil probe with LoRa Mesh communication and can send measurements directly to a Mesh gateway or through other Mesh Nodes.

The probe uses a solid AgCl reference electrode and a pure-metal pH-sensitive electrode. Internal temperature compensation improves pH stability within the specified compensation range.

Soil pH measurements depend strongly on installation conditions, soil moisture, electrode condition, and stabilization time. Correct preparation, installation, and maintenance are necessary for representative results.

1.2 Features

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

1.3 Specifications

Common DC characteristics

Item	Specification
Main unit operating voltage	Approximately 2.5 V to 3.6 V
Main unit operating temperature	-40 °C to 85 °C; battery operating temperature is subject to the battery specification

Soil pH

Item	Specification
Range	3 to 10 pH
Resolution	0.01 pH
Accuracy	±2 % under the specified conditions
Temperature compensation	0 °C to 50 °C; frozen soil can reduce accuracy

Soil temperature

Item	Specification
Range	-40 °C to 85 °C
Resolution	0.1 °C
Accuracy	±0.5 °C from 10 °C to 40 °C; ±0.8 °C outside this range

Soil pH probe

Item	Specification
Operating voltage	5 V to 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 to 15 seconds, adaptive
pH stabilization time	Approximately 30 minutes to 24 hours, depending on probe condition and installation
Temperature stabilization time	Less than 5 minutes
Protection rating	IP68
Operating temperature	-10 °C to 70 °C
Cable length	Standard 3.5 m

Mesh 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
Local interfaces	3.3 V UART, BLE
Antenna	Sub-GHz LoRa antenna matching the shipping Region

1.4 Applications

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

1.5 Sleep Mode and Working Mode

In the sleep state, the node disables most functions and remains in low-power standby until its next scheduled wake-up or a user action wakes it.

The intended working cycle is:

Reach scheduled time -> Wake up -> Power and read the pH probe
                     -> Validate and send the measurement
                     -> Wait for a short communication window -> Sleep

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

1.6 Button Operations and LED Status

Button operations and LED indications are common to Dragino Mesh Nodes. See 3.1 Button Operations and LED Status in the Mesh Quick Start for sleep, wake-up, manual reporting, restart, reset, and firmware-upgrade actions.

1.7 BLE and Local Interfaces

SPH01-MS provides 3.3 V UART and BLE local interfaces. BLE can be used for normal APP firmware updates from a PC through PC BLE in FirmwareUpdateUtility.

The mobile upgrade workflow is still under development.

1.8 Enclosure and Mechanical Reference

The following figures show the pin definitions and the solar enclosure dimensions, mounting points, and cable outlets used by SPH01-MS.

Pin definitions

Solar enclosure dimensions and mounting reference

1.9 Probe Wiring and Operating Mode

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

warning

Return the SET terminal to acquisition mode after a probe-level setting or calibration operation. The node cannot perform normal acquisition while the probe remains in setting mode.

1.10 Soil pH Measurement and Installation

1.10.1 Understanding Soil pH and Temperature

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

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. Frozen soil, poor electrode contact, low moisture, contamination, and insufficient stabilization can affect the result.

1.10.2 Before First Use or After Storage

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

Use one of these 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.

1.10.3 Selecting the Measurement Point

Choose a representative location. Avoid stones, buried metal, large roots, fertilizer deposits, drainage channels, and irrigation outlets unless that condition is intentionally being monitored.

For comparisons, use the same preparation, depth, moisture condition, and installation method.

1.10.4 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

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

1.10.5 Permanent Buried Measurement

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 and provide a drip loop.

1.10.6 Installation Check

After installation, confirm that the node obtains plausible pH and temperature readings. Fixed, extreme, or unstable values can indicate insufficient activation, poor contact, dry soil, air gaps, contamination, damaged electrodes, insufficient stabilization, or a connection problem.

1.11 Probe Maintenance

• 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 to 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 for several minutes in 5 % hydrochloric acid until the 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.

Chemical safety

Hydrochloric acid is corrosive. Use suitable personal protective equipment, ventilation, compatible containers, and the site's chemical-handling and disposal procedures. Rinse the probe thoroughly with purified water after acid cleaning.

2. Use SPH01-MS with a Mesh Gateway

2.1 How It Works

Mesh reporting and gateway decoding for SPH01-MS are currently under development. When 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 and gateway layout will be finalized with the production firmware and decoder.

2.2 Quick Guide to Connect SPH01-MS to a Mesh Gateway

2.2.1 Preparation

1. Confirm that the product label shows SPH01-MS.
2. Install the LoRa antenna before powering or waking the node.
3. Place the solar panel where it receives stable, unobstructed sunlight.
4. Inspect the probe and cable for transport damage.
5. Activate the probe if it is new, recently cleaned, or has remained unused for more than seven days.

2.2.2 Enrollment and Probe Test

For the complete gateway and enrollment procedure, see 2. First network test.

1. Configure the node and Mesh gateway for the Region corresponding to the installation country.
2. Add the node to the gateway with its Dev EUI and App Key.
3. Confirm that the gateway lists the node as enrolled.
4. Before burial, confirm that the firmware can read pH and soil temperature from the probe.

2.2.3 Installation and Final Check

1. Prepare and install the probe according to Section 1.10.
2. Secure the enclosure and protect the cable routing.
3. Allow sufficient stabilization time before treating the first reading as a baseline.
4. When Mesh reporting is available, verify the pH, soil temperature, and device status on the gateway.

2.3 Mesh Payload

The Mesh payload specification for this product will be added in a future documentation update.

2.4 Calibration

The probe supports 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 one supported 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 user-facing SPH01-MS calibration workflow is currently under development. The tool or Mesh interface, command, confirmation, and return to acquisition mode will be added in a future documentation update.

3. Configure SPH01-MS

3.1 Configuration Method

Common Mesh configuration is managed through the Mesh gateway. Use the Mesh Quick Start for the current configuration and enrollment workflow.

3.2 Region and Radio Preset

New units, factory-reset units, and units whose saved configuration has been cleared start with EU868 and the LONG_FAST modem preset (SF11 / BW 250 kHz).

Before deployment, configure the node and gateway for the Region corresponding to the installation country and confirm that their Region settings match.

3.3 Scheduled and Manual Reporting

The final scheduled Mesh reporting and manual-report behavior for SPH01-MS are currently under development. This section will be updated when the production firmware workflow is available.

4. Battery & Power Consumption

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

SPH01-MS uses a solar panel and a 3000 mAh rechargeable lithium battery. The pH probe can require a longer active period than faster environmental sensors.

Battery Info & Power Consumption Analyze.

5. Firmware Update

Use only APP firmware built for SPH01-MS and the device's shipping Region.

For the firmware preparation and upload procedure, see 2. How to upload the firmware.

The mobile upgrade feature is still under development.

6. FAQ

6.1 Why must the probe be activated before measurement?

A new, recently cleaned, or long-stored electrode requires moisture and stabilization before it can provide a representative pH reading. Soak it in pure water for approximately 24 hours or pre-bury it in moist soil for at least 24 hours.

6.2 Why is the pH reading slow, fixed, or unstable?

Check probe activation, soil moisture, electrode cleanliness, soil contact, stones, air gaps, cable movement, damage, and stabilization time. A valid Modbus response within seconds does not mean the field pH has already stabilized.

6.3 Why is no pH or temperature reading available?

Check probe power, cable connection, RS-485 communication, SET operating mode, and probe warm-up time. Confirm that the SET terminal has returned to acquisition mode.

6.4 When will user calibration be available?

The probe supports calibration at pH 4.00, pH 6.86, and pH 9.18. The customer-facing SPH01-MS calibration procedure is currently under development and will be added in a future documentation update.

For enrollment, Region, gateway connectivity, general power, or firmware-update questions, see the general Mesh FAQ.

7. Order Info

Ordering details and Region-specific part numbers for SPH01-MS will be added when the product options are finalized.

8. Packing Info

Package contents, dimensions, and weights for SPH01-MS will be added in a future documentation update.

9. Support

Dragino support is available Monday to Friday from 09:00 to 18:00 GMT+8. When requesting assistance, provide the product model, firmware identification, Region, probe condition, installation method, and the steps required to reproduce the problem.

Contact: Support@dragino.cc