NT18B07 Modbus Register Map and Arduino Tutorial: 7-Channel RS485 NTC Temperature Monitoring

Introduction

Looking for an RS485 temperature acquisition module that can communicate with Arduino, PLCs, or other Modbus RTU controllers?

The Eletechsup NT18B07 is a 7-channel NTC temperature acquisition module designed to collect temperature measurements and transmit the results over an RS485 interface using Modbus RTU.

For developers building industrial monitoring equipment, environmental data loggers, or multi-point temperature measurement systems, understanding the Modbus register map is an essential first step.

This guide introduces the NT18B07 communication settings, temperature registers, data conversion, and a basic Arduino integration approach.

1. NT18B07 Modbus RTU Communication Parameters

The module uses Modbus RTU over RS485. Its documented default communication parameters are:

Parameter	Default setting
Communication interface	RS485
Protocol	Modbus RTU
Slave address	1
Baud rate	9600 bps
Data bits	8
Parity	None
Stop bits	1
Temperature channels	7
Temperature register unit	0.1°C
Supply voltage	DC 6–24V

These settings provide a starting point for communication with compatible Modbus masters. Confirm the actual hardware revision and its manual before commissioning a system.

2. NT18B07 Temperature Register Map

The seven temperature channels are available through consecutive holding registers.

Channel	Register address	Temperature unit
CH1	0x0000	0.1°C
CH2	0x0001	0.1°C
CH3	0x0002	0.1°C
CH4	0x0003	0.1°C
CH5	0x0004	0.1°C
CH6	0x0005	0.1°C
CH7	0x0006	0.1°C

Each temperature reading occupies one 16-bit register.

For example, a raw register value of 253 represents 25.3°C. Negative temperatures must be decoded as signed 16-bit values. A reported sensor-error value must also be handled separately rather than displayed as a real temperature.

Some Modbus software uses one-based register references instead of zero-based hexadecimal offsets. Check the addressing convention of your master software when configuring the register map.

3. Reading NT18B07 with Arduino

An Arduino can communicate with the NT18B07 through a compatible RS485 transceiver, such as a suitable MAX485-based interface, and a Modbus RTU library.

The general connection arrangement is:

• NT18B07 RS485 A and B → RS485 transceiver A and B

• Transceiver RO → Arduino RX

• Arduino TX → transceiver DI

• Transceiver DE and RE → a suitable Arduino direction-control pin

• NT18B07 power input → a regulated DC supply within its specified voltage range

• Arduino and transceiver logic grounds → connected as required by the interface design

Verify the transceiver's voltage compatibility and wiring requirements before powering the circuit.

Example Arduino Code

The following example uses the commonly available ModbusMaster library and SoftwareSerial. It illustrates reading seven consecutive holding registers using the default slave address.

#include <ModbusMaster.h>
#include <SoftwareSerial.h>

#define RS485_DIR 4

SoftwareSerial rs485(2, 3);  // RX, TX
ModbusMaster node;

void preTransmission() {
  digitalWrite(RS485_DIR, HIGH);
}

void postTransmission() {
  digitalWrite(RS485_DIR, LOW);
}

void setup() {
  pinMode(RS485_DIR, OUTPUT);
  digitalWrite(RS485_DIR, LOW);

  Serial.begin(9600);
  rs485.begin(9600);

  node.begin(1, rs485);
  node.preTransmission(preTransmission);
  node.postTransmission(postTransmission);
}

void loop() {
  uint8_t result = node.readHoldingRegisters(0x0000, 7);

  if (result == node.ku8MBSuccess) {
    for (uint8_t i = 0; i < 7; i++) {
      uint16_t raw = node.getResponseBuffer(i);

      // Check the documented sensor-error code first.
      if (raw == 0xF555) {
        Serial.print("CH");
        Serial.print(i + 1);
        Serial.println(": Sensor error");
        continue;
      }

      int16_t signedRaw = (int16_t)raw;
      float temperatureC = signedRaw / 10.0f;

      Serial.print("CH");
      Serial.print(i + 1);
      Serial.print(": ");
      Serial.print(temperatureC, 1);
      Serial.println(" C");
    }
  } else {
    Serial.print("Modbus error: 0x");
    Serial.println(result, HEX);
  }

  delay(2000);
}

Important: This is an integration example, not a guarantee of operation on every Arduino board or RS485 adapter. Verify the module's error-value convention, register map, and sensor behavior against the applicable manual. The RS485 direction-control logic and serial implementation may also need adjustment for your hardware.

4. Other Integration Possibilities

The NT18B07 can be considered for several types of applications that require multi-point temperature acquisition.

Arduino and DIY electronics: Build temperature monitoring prototypes, data loggers, and embedded control systems.

PLC and industrial automation: Read temperature registers through a compatible Modbus RTU master interface.

Home Assistant and IoT gateways: Forward acquired measurements to a compatible automation platform through an appropriate RS485 interface and software configuration.

Environmental monitoring: Collect readings from several NTC probes installed at different measurement points.

The module provides the temperature acquisition interface; visualization, data storage, alerts, and control logic are implemented by the host system.

5. Troubleshooting Common Modbus Problems

If the NT18B07 does not return valid readings, check these items:

1. Confirm the slave address and baud rate.

2. Verify the RS485 A/B wiring and transceiver direction control.

3. Check that the master uses the correct holding-register function.

4. Confirm whether the software expects zero-based or one-based register addresses.

5. Apply the correct signed-value conversion and temperature scaling.

6. Inspect sensor connections if a sensor-error value is returned.

7. Check grounding, cable quality, termination, and biasing where appropriate.

Testing one register first and then expanding to all seven channels is often a useful way to isolate configuration problems.

Conclusion

The Eletechsup NT18B07 provides a practical option for developers who need seven-channel NTC temperature acquisition over RS485 using Modbus RTU.

By understanding its register map and communication parameters, engineers can evaluate integration with Arduino, PLCs, industrial gateways, and compatible monitoring platforms.

For product specifications and further information, visit Eletechsup.

Technical reference: lamaPLC NT18B07 documentation