will be read-only starting December 31st, 2018. For more info please look at this Forum Post

This Sketch reads the Temperature from the Texas Instruments TMP75 sensor using I2C communication. The temperature is read, sent to the serial port and to a 2 line by 16 Character TM162AD Hitachi based LCD.

Help from for the bitwise Arithmetic, thanks.

No promise or claims of originality , quality or code correctness is made or implied. YMMV. Enjoy :).


// Arduino Sketch to read the Texas Instruments 
// TMP75 Temperature Sensor
//  It uses the I2C in the Wire Library
//  Written by J.Park jim(_dot_)buzz(_at_)gmail(_dot_)com
//  23 April 2012 reference 

// Define includes
#include <LiquidCrystal.h>
#include <Wire.h>        // Wire header file for I2C and 2 wire

// I used a Sensor PCB from a scrapped White Intel based iMac
// Note there are two sensor boards both with a TMP75 sensor in the iMac.

// TMP75 Address is 0x48 and from its Datasheet = A0,A1,A2 are all grounded.
int TMP75_Address = 0x48; // Apple iMac Temp Sensor Circular PCB
//int TMP75_Address = 0x49; // Apple iMac Temp Sensor Square PCB

// LCD pinouts used (rs, enable, d4, d5, d6, d7) 
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

// Declare some nice variables
int decPlaces = 1;
int numOfBytes = 2;
int baudRate = 9600;
int columns = 16;   // LCD is 16 Column 2 Row Hitachi LCD
int rows = 2;
byte configReg = 0x01;  // Address of Configuration Register
byte bitConv = B01100000;   // Set to 12 bit conversion
byte rdWr = 0x01;       // Set to read write
byte rdOnly = 0x00;    // Set to Read
String temperature, SerialDegC, lcdDegC;

// Setup the Arduino LCD (Columns, Rows)
void setup(){
  lcd.begin(columns, rows);          // set up the LCD's number of rows and columns:
  Serial.begin(baudRate);            // Set Serial Port speed
  Wire.begin();                      // Join the I2C bus as a master
  SerialDegC += char(176);           // Setup a Degrees C Serial symbol
  SerialDegC += "C ";
  lcdDegC += char(223);              // Setup a Degrees C LCD Symbol
  lcdDegC += "C ";
  Wire.beginTransmission(TMP75_Address);       // Address the TMP75 sensor
  Wire.write(configReg);                       // Address the Configuration register 
  Wire.write(bitConv);                         // Set the temperature resolution 
  Wire.endTransmission();                      // Stop transmitting
  Wire.beginTransmission(TMP75_Address);       // Address the TMP75 sensor
  Wire.write(rdOnly);                          // Address the Temperature register 
  Wire.endTransmission();                      // Stop transmitting 

// Main Program Infinite loop 
void loop(){
  float temp = readTemp();             // Read the temperature now
  Serial.print(temp,decPlaces);        // Temperature value to 1 Decimal place no newline to serial
  Serial.println(SerialDegC);          // Degree symbol after the temperature value with newline  
  lcd.setCursor(2,0);                  // Set Cursor position (Column,Row)
  lcd.print("Temperature  *");         // Print string to LCD
  lcd.setCursor(5,1);                  // Set Cursor position (Column,Row)
  lcd.print(temp,decPlaces);           // Print temperature value to 1 Decimal place no newline
  delay(500);                          // Slow the reads down so we can follow the output
  lcd.print("Temperature   ");

// Begin the reading the TMP75 Sensor 
float readTemp(){
  // Now take a Temerature Reading
  Wire.requestFrom(TMP75_Address,numOfBytes);  // Address the TMP75 and set number of bytes to receive
  byte MostSigByte =;              // Read the first byte this is the MSB
  byte LeastSigByte =;             // Now Read the second byte this is the LSB

  // Being a 12 bit integer use 2's compliment for negative temperature values
  int TempSum = (((MostSigByte << 8) | LeastSigByte) >> 4); 
  // From Datasheet the TMP75 has a quantisation value of 0.0625 degreesC per bit
  float temp = (TempSum*0.0625);
  Serial.println(MostSigByte, BIN);   // Uncomment for debug of binary data from Sensor
  Serial.println(LeastSigByte, BIN);  // Uncomment for debug  of Binary data from Sensor
  return temp;                           // Return the temperature value