What is a Si7051 sensor ?

The Si7051 is a precision digital temperature sensor that uses the I²C bus to communicate directly with a microcontroller.

Based on patented CMOS technology, it offers exceptional long-term stability and laboratory-grade accuracy in a tiny form factor.

It is often used as a reference sensor in:

• low-power IoT systems,
• medical connected devices,
• data loggers and calibration devices.

Operating principle

The sensor integrates:

• an ultra-stable CMOS thermal detection element,
• a 14-bit analog-to-digital converter,
• and an internal processor that applies the calibration curve stored in EEPROM.

The temperature is calculated from a raw code (Tcode) according to the formula provided by Silicon Labs:

T(°C) = (175,72 × T_code) / 2¹⁶ − 46,85

💡 The calibration coefficients are factory integrated and guaranteed across the entire range.

Voltage / Temperature Curve

The Si7051 does not output an analog voltage, but we can visualize the equivalent digital curve:

💡 The relationship is almost linear, ideal for digital processing without recalibration.

Operating principle

#include <Wire.h>
#define SI7051_ADDR 0x40
#define CMD_MEASURE_TEMP 0xF3

void setup() {
  Serial.begin(9600);
  Wire.begin();
}

void loop() {
  Wire.beginTransmission(SI7051_ADDR);
  Wire.write(CMD_MEASURE_TEMP);
  Wire.endTransmission();
  delay(15);
  Wire.requestFrom(SI7051_ADDR, 2);
  uint16_t raw = (Wire.read() << 8) | Wire.read();
  float tempC = ((175.72 * raw) / 65536.0) - 46.85;
  Serial.print("Température : ");
  Serial.print(tempC, 2);
  Serial.println(" °C");
  delay(1000);
}

✅ Example of result:

Temperature: 23.72 °C

Principle diagram (I2C connection)

+3.3V
 │
[Si7051]
 │ SDA ───────┐
 │ SCL ───────┤── MCU (Arduino, STM32, ESP32…)
 │ GND

💡 4.7 kΩ pull-up resistors recommended on SDA/SCL.

Application areas

🧠 Medical equipment and wearables

🏭 Precise industrial measurements

🧪 Instrumentation and calibration

🌿 IoT sensors and connected objects

🔋 Battery-powered systems