The LM75, also known as the CJMCU-75, is a versatile I2C-supported temperature sensor module. Despite its compact design, it offers precise temperature monitoring across a wide range, from -55°C to +125°C. Notably, it provides temperature readings in both Celsius and Fahrenheit units, accommodating diverse user preferences. This module seamlessly integrates into various electronic setups, operating with a supply voltage between 2.7 V to 5.5 V, making it compatible with popular controller boards like the ESP8266 and ESP32. Overall, the LM75 is a dependable choice for accurate temperature monitoring in a range of applications.

 

Package Includes:

• 1x LM75 Temperature Sensor Module
  
  

Features:

• I2C Support: The CJMCU-75 module is equipped with I2C communication support, enabling easy and standardized data exchange for temperature readings.
• Wide Temperature Range: It operates across an extensive temperature range, spanning from -55°C to +125°C, making it suitable for monitoring temperature in diverse environmental conditions.
• Dual Temperature Units: This module provides temperature measurements in both Celsius and Fahrenheit units, catering to user preferences and application requirements.
• Low Power Shutdown Mode: It offers a low-power shutdown mode, consuming only 4uA of current when powered with 3 volts, making it energy-efficient and suitable for battery-powered applications.
• Overtemperature Functionality: The CJMCU-75 module features an overtemperature pin that can serve as both an interrupt and a thermostat input, enhancing its versatility in temperature monitoring and control.
• Multi-Host Connectivity: It has the capability to connect up to eight different hosts to a single device, simplifying centralized temperature monitoring and control in complex systems.
• Stand-Alone Operation: This module can function independently as a thermostat, making it suitable for applications where autonomous temperature control is required.

•  

Description:

The LM75, also known as the CJMCU-75, represents a versatile and dependable I2C-supported temperature sensor module. Its compact design belies its powerful capabilities, making it an indispensable component in various applications requiring precise temperature monitoring. operating across a broad temperature spectrum, the LM75 temperature sensor module excels in ensuring temperature accuracy even in demanding conditions. Its operational temperature range spans from -55°C to +125°C, offering reliable performance in a wide range of environmental scenarios. one of the standout features of the LM75 module is its ability to provide temperature readings in both Celsius and Fahrenheit units. This flexibility caters to the diverse preferences and requirements of users across different applications. The LM75 module is designed to seamlessly integrate into different electronic setups. It operates effectively with a single supply voltage ranging from 2.7 V to 5.5 V. This wide voltage compatibility ensures smooth integration with a variety of controller boards, whether they operate at 3.3V or 5V. Popular controller boards like the ESP8266 and ESP32 can readily incorporate the LM75 module.

 

Principle of Work:

the LM75 temperature sensor combines internal temperature sensing capabilities with I2C communication, allowing an MCU to efficiently monitor and control temperature, while offering flexibility in setting temperature thresholds and alarm conditions. This makes it a valuable component for various thermal management and protection applications:

Internal Operation:

• Temperature Sensing: The LM75 uses its internal temperature sensor to continuously monitor the ambient temperature.
• I2C Interface: It communicates temperature data to an external host, typically an MCU, through the I2C interface. The host can request temperature readings from the LM75 at any time.
• Overtemperature Detection: The LM75 includes a programmable temperature limit. When the temperature exceeds this limit, the open-drain overtemperature output (OS) is activated. This output can sink current, alerting the host to the overtemperature condition.
• Operating Modes: The OS output can operate in two modes: comparator and interrupt. In the comparator mode, the host sets a temperature threshold (TOS), and when the temperature surpasses this threshold, the OS output is activated. In the interrupt mode, the OS output functions as an interrupt pin, signaling the host when the temperature exceeds TOS.
• Hysteresis Control: The host can also control the hysteresis temperature (THYST), which defines the temperature at which the alarm condition is considered invalid. This prevents frequent toggling of the alarm signal near the threshold.
• Address Configuration: The LM75 uses three pins to set its address, allowing multiple LM75 devices to operate on the same I2C bus without conflicts.

Integration with MCU:

• Temperature Readings: The MCU communicates with the LM75 via the I2C interface to request temperature readings as needed for monitoring and control purposes.
• Threshold Configuration: The MCU can set the overtemperature threshold (TOS) and hysteresis temperature (THYST) based on the specific temperature range and application requirements.
• Alert Handling: When an overtemperature condition is detected, the MCU can respond accordingly, taking actions such as activating cooling mechanisms or generating alerts.
• Address Management: If multiple LM75 sensors are used on the same I2C bus, the MCU ensures proper address configuration to communicate with each sensor individually.
• Power Supply: The LM75 operates within a supply voltage range of 3.0V to 5.5V, making it compatible with the MCU's power requirements.

 

Pinout of the Board:

Pin Name	Function
VCC	Positive power supply pin
GND	Reference potential pin
SCL	The I2C clock signals, is a pull-up resistor is necessary on the I2C line. However, this module streamlines the process by incorporating built-in pull resistors, eliminating the need for external pull-up resistors.
SDA	Open-drain Serial Data PIN for I2C communication. Normally, an external pull-up resistor is needed on the I2C line to ensure proper data transmission. However, this module comes equipped with built-in pull-up resistors, eliminating the need for additional external resistors.
OS	Over-temperature Shutdown Output pin

 

Applications:

1. Environmental Monitoring: The module is widely used in environmental monitoring systems to measure and record temperature data in various settings, including indoor and outdoor environments.
2. Thermal Management: It plays a crucial role in thermal management systems for electronic devices and components, ensuring they operate within safe temperature ranges.
3. Industrial Automation: The LM75 module is utilized in industrial automation to monitor temperature conditions in manufacturing processes, ensuring product quality and equipment safety.
4. HVAC Systems: Heating, Ventilation, and Air Conditioning (HVAC) systems use the LM75 to regulate temperature, providing comfort and energy efficiency in residential and commercial buildings.
5. Server Rooms and Data Centers: Temperature control is critical in server rooms and data centers. The LM75 helps maintain the ideal temperature to prevent overheating and equipment damage.
6. Automotive Applications: The module is employed in automotive applications for monitoring engine temperature, cabin temperature, and other critical thermal parameters.
7. Energy Efficiency: It contributes to energy-efficient systems by enabling precise control of heating, cooling, and ventilation in appliances like refrigerators and air conditioners.
8. Weather Stations: LM75 modules are integrated into weather stations to measure ambient temperatures and provide accurate weather data.
9. Medical Equipment: The module ensures temperature accuracy in medical devices like incubators, laboratory equipment, and blood storage units.
10. Home Automation: In smart homes, it assists in temperature control, allowing users to adjust heating and cooling systems remotely for energy savings and comfort.
11. Power Management: It helps manage the operating temperature of power electronics, such as voltage regulators and power supplies, to maintain their efficiency and reliability.
12. Agriculture: In agriculture, LM75 modules are used for monitoring soil and environmental conditions, ensuring optimal conditions for crops and livestock.
13. Cold Chain Management: The LM75 is integral to maintaining temperature-sensitive products during transportation and storage in the pharmaceutical and food industries.

 

Circuit:

1. Power Supply Connection:

   • To provide power to the LM75 temperature sensor module, connect its VCC pin to the 3.3V pin on the Arduino UNO.
   • Connect the GND (ground) pin of the LM75 module to the GND pin on the Arduino UNO. This establishes the common ground reference for the module and the Arduino.

2. Serial Data Communication:

   • For sending and receiving serial data, you'll need to establish a connection between the LM75 module and the Arduino UNO.
   • Connect the LM75's SDA (Serial Data) pin to the Arduino's A4 pin. This connection is essential for bidirectional data transfer between the module and the Arduino.
   • Additionally, connect the LM75's SCL (Serial Clock) pin to the Arduino's A5 pin. This connection enables the synchronization of data transmission between the two devices.

 

Library: 

 

1. Download the Library Zip File:

   • Visit the GitHub repository page: https://github.com/jlz3008/lm75
   • Click the green "Code" button on the right side of the page.
   • Select "Download ZIP" to download the library as a compressed zip file.

2. Install the Library in Arduino IDE:

   • Open your Arduino IDE.

3. Import the Library:

   • Go to "Sketch" -> "Include Library" -> "Add .ZIP Library..."

4. Locate and Select the Downloaded ZIP File:

   • In the file dialog that appears, navigate to the location where you downloaded the LM75 library ZIP file.
   • Select the ZIP file and click the "Open" button.

5. Library Installation Confirmation:

   • The Arduino IDE will extract and install the library.
   • Once installed, you should see a message in the Arduino IDE's status bar indicating that the library was successfully added.

 

Code:

The code continuously reads and displays the LM75 temperature sensor's temperature in degrees Celsius on the Arduino's serial monitor. It's a simple temperature monitoring program that can be useful in various applications where temperature data needs to be collected and analyzed:

#include "Wire.h" // Include the Wire library for I2C communication
#include "lm75.h" // Include the LM75 library

TempI2C_LM75 Temperature(0x48, TempI2C_LM75::nine_bits); // Create an LM75 object

void setup() {
  Serial.begin(9600);
  Serial.println("Temperature Monitor");
}

void loop() {
  float tempCelsius = Temperature.getTemp(); // Read temperature in Celsius
  Serial.print("Temperature: ");
  Serial.print(tempCelsius);
  Serial.println(" °C");

  delay(2000); // Delay for 2 seconds before the next reading
}

1. It includes the necessary libraries for I2C communication (Wire.h) and for working with the LM75 temperature sensor (lm75.h).

2. It creates an LM75 object named Temperature with an I2C address of 0x48 and a resolution of nine bits. This object represents the LM75 temperature sensor.

3. In the setup() function:

   • It initializes serial communication at a baud rate of 9600, allowing you to send data to and receive data from your computer.
   • It prints "Temperature Monitor" to the serial monitor to indicate that the program is running.

4. In the loop() function:

   • It reads the temperature from the LM75 sensor using the Temperature.getTemp() method, which returns the temperature in Celsius.
   • It stores the temperature in the tempCelsius variable.
   • It prints the temperature value along with a "Temperature:" label to the serial monitor.
   • It adds "°C" to indicate that the temperature is in degrees Celsius.
   • It then waits for 2 seconds (2000 milliseconds) using delay(2000) before taking the next temperature reading.

 

Technical Details:

• Operating Voltage: 3.3 Volts – 5.0 Volts
• Temperature Range: -55°C – 125°C
• Temperature Conversion time: 100ms
• Supply Current: 250uA
• Maximum Supply Current: 1mA
• OS Sink Current: 10mA
• Delta-sigma Resolution: 8-bits
• TOS temperature: 80°C
• THYST temperature: 75°C

 

Resources:

• LM75 Arduino Library.
• Tutorial

Comparisons:

Comparing the LM75 temperature sensor module to the DHT11 module involves considering several aspects of these two sensors, If you need precise temperature readings over a wide range and don't require humidity data, the LM75 is a better choice. However, if you need both temperature and humidity measurements on a budget, the DHT11 is a suitable option:

1. Sensor Type:

• LM75: The LM75 is a digital temperature sensor that provides precise temperature readings in degrees Celsius or Fahrenheit. It communicates via the I2C protocol.

• DHT11: The DHT11 is a digital temperature and humidity sensor. It provides both temperature and humidity readings and communicates using a single-wire digital interface.

2. Temperature Range:

• LM75: The LM75 has a wide temperature range, typically from -55°C to +125°C.

• DHT11: The DHT11 has a more limited temperature range, typically from 0°C to 50°C.

3. Accuracy:

• LM75: The LM75 offers high accuracy in temperature measurements, typically within ±2°C.

• DHT11: The DHT11 provides decent accuracy for most applications but may have slightly larger temperature measurement errors, typically within ±2°C.

4. Humidity Measurement:

• LM75: The LM75 is solely a temperature sensor and does not measure humidity.

• DHT11: The DHT11 not only measures temperature but also provides humidity readings, making it suitable for applications requiring both temperature and humidity data.

5. Interface:

• LM75: The LM75 uses the I2C interface, which is widely supported by microcontrollers and allows for easy integration into various projects.

• DHT11: The DHT11 uses a single-wire digital interface, which is also straightforward to use but may require specific libraries for some microcontrollers.

6. Power Consumption:

• LM75: The LM75 has a low power consumption, making it suitable for battery-powered applications.

• DHT11: The DHT11 is relatively low-power but may consume slightly more power than the LM75 due to its humidity measurement.

8. Applications:

• LM75: The LM75 is commonly used in industrial and scientific applications where high accuracy and a wide temperature range are required. It's also suitable for environmental monitoring and HVAC systems.

• DHT11: The DHT11 is often used in home automation, weather stations, and simple DIY projects where basic temperature and humidity monitoring is sufficient.