How to Use LPS25HB: Examples, Pinouts, and Specs

The LPS25HB is a digital barometer and pressure sensor manufactured by STMicroelectronics. It is designed to provide high-resolution pressure measurements with excellent accuracy and stability. The sensor operates over a wide range of pressures (260 hPa to 1260 hPa) and temperatures (-30°C to +105°C), making it ideal for a variety of applications.

• Weather monitoring and forecasting
• Altitude measurement for drones and aviation
• Environmental sensing in IoT devices
• Indoor navigation and floor detection
• Wearable devices for fitness and health tracking

The following table summarizes the key technical details of the LPS25HB:

The LPS25HB is available in a 10-pin HLGA package. The pinout is as follows:

1. Power Supply: Connect the VDD pin to a regulated power supply (1.7 V to 3.6 V) and the GND pin to ground.
2. Communication Interface: Choose between I²C or SPI for communication:
   • For I²C, connect the SCL and SDA pins to the corresponding lines on the microcontroller.
   • For SPI, connect the SPC, SDI/SDO, and CS pins to the SPI interface of the microcontroller.
3. Pull-Up Resistors: If using I²C, add pull-up resistors (typically 4.7 kΩ) to the SCL and SDA lines.
4. Interrupts: Optionally, connect the INT1 and/or INT2 pins to the microcontroller for event-driven operation.
5. Reserved Pins: Leave the reserved pins (8, 9, 10) unconnected.

• Ensure the supply voltage is within the specified range to avoid damage to the sensor.
• Use decoupling capacitors (e.g., 0.1 µF) near the VDD pin to reduce noise.
• Avoid exposing the sensor to extreme environmental conditions beyond its operating range.
• When using SPI, ensure the CS pin is properly toggled to select the device.

The following example demonstrates how to interface the LPS25HB with an Arduino UNO using the I²C protocol:

#include <Wire.h>

// LPS25HB I2C address
#define LPS25HB_ADDRESS 0x5C

// Register addresses
#define LPS25HB_WHO_AM_I 0x0F
#define LPS25HB_PRESS_OUT_XL 0x28
#define LPS25HB_CTRL_REG1 0x20

void setup() {
  Wire.begin(); // Initialize I2C communication
  Serial.begin(9600); // Initialize serial communication for debugging

  // Check sensor identity
  Wire.beginTransmission(LPS25HB_ADDRESS);
  Wire.write(LPS25HB_WHO_AM_I);
  Wire.endTransmission();
  Wire.requestFrom(LPS25HB_ADDRESS, 1);
  if (Wire.available()) {
    byte whoAmI = Wire.read();
    if (whoAmI == 0xBD) { // Expected WHO_AM_I value for LPS25HB
      Serial.println("LPS25HB detected!");
    } else {
      Serial.println("Sensor not detected. Check connections.");
      while (1); // Halt execution
    }
  }

  // Configure the sensor (enable and set output data rate)
  Wire.beginTransmission(LPS25HB_ADDRESS);
  Wire.write(LPS25HB_CTRL_REG1);
  Wire.write(0x90); // Power on, ODR = 1 Hz
  Wire.endTransmission();
}

void loop() {
  // Read pressure data
  Wire.beginTransmission(LPS25HB_ADDRESS);
  Wire.write(LPS25HB_PRESS_OUT_XL | 0x80); // Auto-increment address
  Wire.endTransmission();
  Wire.requestFrom(LPS25HB_ADDRESS, 3);

  if (Wire.available() == 3) {
    uint8_t xl = Wire.read();
    uint8_t l = Wire.read();
    uint8_t h = Wire.read();
    int32_t pressure_raw = (int32_t)((h << 16) | (l << 8) | xl);
    float pressure_hPa = pressure_raw / 4096.0; // Convert to hPa
    Serial.print("Pressure: ");
    Serial.print(pressure_hPa);
    Serial.println(" hPa");
  }

  delay(1000); // Wait 1 second before next reading
}

1. Sensor Not Detected

   • Cause: Incorrect I²C address or wiring.
   • Solution: Verify the I²C address (default is 0x5C) and check the connections.

2. No Pressure Readings

   • Cause: Sensor not powered or misconfigured.
   • Solution: Ensure the VDD pin is connected to a proper power supply and the CTRL_REG1 register is configured correctly.

3. Inaccurate Measurements

   • Cause: Environmental interference or improper calibration.
   • Solution: Avoid placing the sensor near heat sources or strong air currents. Perform calibration if necessary.

• Q: Can the LPS25HB measure altitude?
  A: Yes, the sensor can calculate altitude based on pressure readings using the barometric formula.

• Q: What is the maximum cable length for I²C communication?
  A: The maximum length depends on the pull-up resistor values and the capacitance of the cable. Typically, it is limited to a few meters.

• Q: Is the LPS25HB waterproof?
  A: No, the sensor is not waterproof. Use a protective enclosure if operating in humid or wet environments.