IS4350-M1 Arduino Temperature Sensor

A Modbus TCP/IP temperature sensor built with an Arduino Uno, a TMP36 and the INACKS IS4350-M1 module.

The IS4350-M1 puts the IS4350 Modbus TCP/IP server IC, a LAN8742A Ethernet PHY, the Ethernet magnetics and an RJ45 connector on a single module. Your Arduino talks to it over I2C, as if it were an I2C memory, and the module takes care of Ethernet, TCP/IP and Modbus. This example reads a TMP36 and publishes the temperature in a Holding Register that any Modbus TCP/IP client (PLC, SCADA, HMI or PC) can read.

No Ethernet or Modbus library is needed, only the standard Wire library.

flowchart LR
    T["TMP36"] -->|analog| A["Arduino Uno"]
    A -->|I2C| M["IS4350-M1"]
    M -->|"Modbus TCP/IP (Ethernet)"| C["PLC / SCADA / PC"]

Loading

Features

• Reads a TMP36 on A0 once per second
• Publishes the temperature in Holding Register 0 (HOLD_0) as a signed 16-bit value in 0.1 °C
• Gets its IP address by DHCP and prints it on the Serial Monitor
• Writes a valid reading before the Modbus server goes online, so a client never reads uninitialized data
• Checks that the module answers before doing anything else

Hardware

Qty	Part
1	Arduino Uno
1	IS4350-M1 module
1	TMP36 temperature sensor
2	4.7 kΩ resistors (I2C pull-ups)
1	3.3 V regulator to power the module
1	Ethernet cable and a network with a DHCP server

Other Arduino boards work too, as long as their I2C supports clock stretching, which the IS4350 uses. Connect the module to the board's SDA and SCL pins.

Wiring

TMP36

TMP36	Arduino Uno
+Vs	5V
Vout	A0
GND	GND

With the flat side facing you and the legs down, the pins are +Vs, Vout and GND from left to right.

IS4350-M1

IS4350-M1 pin	Connect to	Notes
3V3 (7, 35)	3.3 V regulator output	Do not use the Uno 3.3V pin (50 mA max)
GND	Arduino GND and regulator GND	Common ground
SDA (2)	A4	4.7 kΩ pull-up to 5 V
SCL (1)	A5	4.7 kΩ pull-up to 5 V
SPD (3)	GND	I2C at 100 kHz
ADR (4)	GND	I2C address 24
RJ45	Switch or router	The network needs a DHCP server
All other pins	—	Leave floating

Note

The IS4350 alone can draw up to 90 mA, plus the Ethernet PHY, so the module needs its own 3.3 V regulator (for example, an LDO fed from the Uno's 5V pin). SDA and SCL are 5 V tolerant, so the pull-ups go to the Uno's 5 V. SPD and ADR are read only at power-up and must never be left floating.

Getting started

1. Clone this repository. The Arduino IDE needs the sketch inside a folder with the same name:

   .
   ├── README.md
   └── IS4350_M1_Temperature_Sensor/
       └── IS4350_M1_Temperature_Sensor.ino

2. Open IS4350_M1_Temperature_Sensor.ino in the Arduino IDE, select Arduino Uno and its port, and click Upload.

   Or with arduino-cli (replace /dev/ttyACM0 with your port):

   arduino-cli core install arduino:avr
   arduino-cli compile --fqbn arduino:avr:uno IS4350_M1_Temperature_Sensor
   arduino-cli upload -p /dev/ttyACM0 --fqbn arduino:avr:uno IS4350_M1_Temperature_Sensor

3. Open the Serial Monitor at 9600 baud. Once the server is online, the sketch prints the IP address and then the temperature every second:

   Status: 2
   Status: 3
   Status: 4
   Sensor online. IP: 192.168.1.57, port 502
   Temperature: 24.7 C
   Temperature: 24.8 C

4. Connect any Modbus TCP/IP client to that IP address and read the temperature.

Reading the temperature

Setting	Value
IP address	Printed on the Serial Monitor
Port	502
Unit ID	255
Function code	03 (Read Holding Registers)
Address	0 (HOLD_0), shown as 40001 in tools that number registers from 1
Quantity	1
Data type	INT16 (signed)
Scale	0.1 °C

HOLD_0	Temperature
235	23.5 °C
0	0.0 °C
-52	-5.2 °C

If your client shows unsigned values, negative temperatures appear above 32767: -52 is shown as 65484 (0xFFCC).

A list of recommended Modbus client applications is on the IS4350 product page.

How it works

The IS4350 memory map has 16-bit registers with 16-bit addresses. The sketch only uses these:

Register	Address	Use
HOLD_0	0	Temperature, written by the Arduino and read by the Modbus client
IP	65501–65504	IP address assigned by DHCP, one byte per register
GO_ONLINE	65513	Write 1 to start the Modbus server
STATUS	65514	Low byte = 5 when the server is ready and listening
CHIP_ID	65522	Always 150, used to check the I2C link

At start-up the sketch:

1. Reads CHIP_ID to check that the module answers.
2. Writes the first reading to HOLD_0.
3. Writes 1 to GO_ONLINE. The server never starts on its own (fail-safe power-up).
4. Polls STATUS until its low byte is 5.
5. Reads the IP registers and prints the address.

Then loop() writes a new reading to HOLD_0 every second.

Every register access is a plain I2C transfer, with the address and the data sent most significant byte first:

Write:  START | ADDR+W | REG_H | REG_L | DATA_H | DATA_L | STOP
Read:   START | ADDR+W | REG_H | REG_L | RESTART | ADDR+R | DATA_H | DATA_L | STOP

ADDR is the 7-bit address 24 (0x18). The helper functions wait 5 ms after each transfer, because the IS4350 needs a few milliseconds between I2C operations.

Customizing

• Another sensor: replace readTemperature() with your own code and keep writing the result to HOLD_0.
• 3.3 V boards: set ADC_REF_MV to 3300 and pull SDA and SCL up to 3.3 V.
• More values: write them to HOLD_1, HOLD_2 and so on. 65,500 Holding Registers are available.
• Another I2C address or speed: ADR selects address 24 (GND), 25 (1.65 V, two 10 kΩ resistors as a divider) or 26 (3.3 V). SPD selects 100 kHz (GND), 400 kHz (1.65 V) or 1 MHz (3.3 V). Update IS4350_ADDR and call Wire.setClock() to match.
• Static IP: stop the server (GO_ONLINE = 0), write 0 to the DHCP register (65500), then write the IP, MASK and GATEWAY registers. See the IS4350 datasheet for the details.

Troubleshooting

Symptom	What to check
IS4350-M1 not detected	Power, GND, SDA/SCL wiring and pull-ups. SPD and ADR must be tied, not floating. They are read at power-up, so power-cycle the module after changing them.
Status stays at 3	No DHCP server answered. Connect the module to a router or switch with DHCP, or set a static IP.
Status 103	The network cable is disconnected. Check the cable and the RJ45 LEDs.
Status 101 or 102	Invalid MAC address configuration. Hold DEF (pin 5) high for 3 s to restore the defaults.
The client can't connect, although the status is 5	Use the printed IP and port 502, and keep the client on the same subnet. Only one client can be connected at a time.
Wrong temperature	Check the TMP36 pinout and that ADC_REF_MV matches your board.

Documentation

• IS4350-M1 product page
• IS4350 product page

The IS4350-M1 user manual (ISDOC155) covers the module pinout, power supply and integration. The IS4350 datasheet (ISDOC139) covers the full register map, the I2C protocol and the safety features.