How to Use alt/bar/temp: Examples, Pinouts, and Specs

The Altimeter Barometric Pressure Sensor, Temperature Sensor Module 29124, manufactured by Parallax Inc., is a versatile sensor module designed to measure atmospheric pressure, altitude, and temperature. This module is based on the Bosch BMP280 sensor, which provides high precision and low power consumption, making it ideal for a wide range of applications.

• Weather monitoring systems
• Altitude measurement in drones and UAVs
• Environmental data logging
• IoT devices for atmospheric sensing
• Educational projects and prototyping

The following table outlines the key technical details of the Altimeter Barometric Pressure Sensor, Temperature Sensor Module 29124:

The module has a total of 6 pins, as described in the table below:

1. Power the Module: Connect the VIN pin to a 3.3V or 5V power source and the GND pin to the ground.
2. Select Communication Mode:
   • For I2C: Connect the CS pin to GND and use the SCL and SDA pins for communication.
   • For SPI: Connect the CS pin to a GPIO pin on your microcontroller and use the SCL, SDA, and SDO pins for SPI communication.
3. I2C Address Selection: Use the SDO pin to set the I2C address:
   • Connect SDO to GND for address 0x76.
   • Connect SDO to VIN for address 0x77.
4. Connect to a Microcontroller: Use appropriate pull-up resistors (typically 4.7 kΩ) on the SCL and SDA lines for I2C communication.

• Ensure the operating voltage matches the microcontroller's logic level (3.3V or 5V).
• Place the sensor in an open area for accurate pressure and temperature readings.
• Avoid exposing the sensor to water, dust, or extreme conditions beyond its specified range.
• Use decoupling capacitors (e.g., 0.1 µF) near the VIN pin to reduce noise.

Below is an example Arduino sketch to read pressure, altitude, and temperature data using the I2C interface:

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BMP280.h>

// Create an instance of the BMP280 sensor
Adafruit_BMP280 bmp; // I2C interface by default

void setup() {
  Serial.begin(9600);
  while (!Serial); // Wait for Serial Monitor to open

  // Initialize the BMP280 sensor
  if (!bmp.begin(0x76)) { // Use 0x77 if SDO is connected to VIN
    Serial.println("Could not find a valid BMP280 sensor, check wiring!");
    while (1); // Halt execution if sensor initialization fails
  }

  // Configure the sensor
  bmp.setSampling(Adafruit_BMP280::MODE_NORMAL,
                  Adafruit_BMP280::SAMPLING_X2,   // Temperature oversampling
                  Adafruit_BMP280::SAMPLING_X16,  // Pressure oversampling
                  Adafruit_BMP280::FILTER_X16,    // Filtering
                  Adafruit_BMP280::STANDBY_MS_500); // Standby time
}

void loop() {
  // Read and print temperature, pressure, and altitude
  Serial.print("Temperature = ");
  Serial.print(bmp.readTemperature());
  Serial.println(" *C");

  Serial.print("Pressure = ");
  Serial.print(bmp.readPressure() / 100.0F); // Convert Pa to hPa
  Serial.println(" hPa");

  Serial.print("Approx. Altitude = ");
  Serial.print(bmp.readAltitude(1013.25)); // Adjust sea level pressure as needed
  Serial.println(" m");

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

1. Sensor Not Detected:

   • Ensure the wiring is correct and matches the selected communication mode (I2C or SPI).
   • Verify the I2C address (0x76 or 0x77) and update the code accordingly.
   • Check for loose connections or damaged wires.

2. Incorrect Readings:

   • Ensure the sensor is placed in a stable environment without rapid temperature or pressure changes.
   • Avoid placing the sensor near heat sources or in direct sunlight.

3. Communication Errors:

   • Use pull-up resistors on the I2C lines if not already present.
   • Check the microcontroller's I2C or SPI configuration and ensure it matches the sensor's settings.

Q: Can this sensor be used with a 5V microcontroller?
A: Yes, the module is compatible with both 3.3V and 5V systems.

Q: How do I calculate altitude from pressure readings?
A: The sensor library provides a readAltitude() function, but you can also use the barometric formula if you need custom calculations.

Q: Can I use this sensor outdoors?
A: While the sensor can operate in a wide temperature range, it is not waterproof or dustproof. Use a protective enclosure for outdoor applications.