How to Use adxl345: Examples, Pinouts, and Specs

The ADXL345 is a small, thin, low-power, 3-axis accelerometer manufactured by Arduino with the part ID "UNO". It provides high-resolution (13-bit) measurements of acceleration up to ±16g. The device features a digital output accessible via I2C or SPI interfaces, making it versatile and easy to integrate into a wide range of applications.

• Motion sensing in portable devices
• Tilt detection for user interface control
• Gesture recognition in gaming and robotics
• Vibration monitoring in industrial systems
• Fall detection in healthcare devices

The ADXL345 is designed for precision and flexibility, with the following key specifications:

The ADXL345 has 8 pins, as described in the table below:

The ADXL345 can be used in either I2C or SPI mode, depending on the application. Below are the steps to integrate the ADXL345 into a circuit and communicate with it using an Arduino UNO.

1. Wiring:

   • Connect the ADXL345's VDD pin to the Arduino's 3.3V pin.
   • Connect the GND pin to the Arduino's GND.
   • Connect the SCL pin to the Arduino's A5 pin (I2C clock line).
   • Connect the SDA pin to the Arduino's A4 pin (I2C data line).
   • Tie the CS pin to VDD to enable I2C mode.
   • Optionally, connect INT1 or INT2 to a digital pin on the Arduino for interrupt handling.

2. Arduino Code Example: Below is an example code snippet to read acceleration data from the ADXL345 using the Arduino Wire library:

   #include <Wire.h>
   
   #define ADXL345_ADDRESS 0x53 // Default I2C address for ADXL345
   #define POWER_CTL 0x2D       // Power control register
   #define DATA_FORMAT 0x31    // Data format register
   #define DATAX0 0x32         // X-axis data register (low byte)
   
   void setup() {
     Wire.begin(); // Initialize I2C communication
     Serial.begin(9600); // Start serial communication for debugging
   
     // Initialize ADXL345
     Wire.beginTransmission(ADXL345_ADDRESS);
     Wire.write(POWER_CTL); // Select power control register
     Wire.write(0x08);      // Set measurement mode
     Wire.endTransmission();
   
     Wire.beginTransmission(ADXL345_ADDRESS);
     Wire.write(DATA_FORMAT); // Select data format register
     Wire.write(0x0B);        // Set full resolution and ±16g range
     Wire.endTransmission();
   }
   
   void loop() {
     int16_t x, y, z;
   
     // Request 6 bytes of acceleration data (X, Y, Z)
     Wire.beginTransmission(ADXL345_ADDRESS);
     Wire.write(DATAX0); // Start reading from DATAX0 register
     Wire.endTransmission(false);
     Wire.requestFrom(ADXL345_ADDRESS, 6);
   
     if (Wire.available() == 6) {
       x = (Wire.read() | (Wire.read() << 8)); // Combine low and high bytes
       y = (Wire.read() | (Wire.read() << 8));
       z = (Wire.read() | (Wire.read() << 8));
     }
   
     // Print acceleration values to Serial Monitor
     Serial.print("X: "); Serial.print(x);
     Serial.print(" Y: "); Serial.print(y);
     Serial.print(" Z: "); Serial.println(z);
   
     delay(500); // Delay for readability
   }
   

• Power Supply: Ensure the ADXL345 is powered with a stable voltage between 2.0V and 3.6V. Using a voltage higher than 3.6V may damage the device.
• Pull-Up Resistors: For I2C communication, use pull-up resistors (typically 4.7kΩ) on the SCL and SDA lines if not already present on the breakout board.
• Interrupts: Configure the INT1 and INT2 pins for advanced features like activity detection or free-fall detection.
• Mounting: Secure the ADXL345 to minimize vibrations or noise that could affect measurements.

1. No Data or Incorrect Readings:

   • Ensure the wiring is correct and matches the pin configuration.
   • Verify that the ADXL345 is in measurement mode by checking the POWER_CTL register.

2. I2C Communication Fails:

   • Check the I2C address (default is 0x53). If the SDO/ALT pin is tied high, the address changes to 0x1D.
   • Ensure pull-up resistors are present on the SCL and SDA lines.

3. Unstable or Noisy Data:

   • Verify that the ADXL345 is securely mounted to avoid mechanical vibrations.
   • Use filtering techniques or adjust the output data rate (ODR) to reduce noise.

Q: Can the ADXL345 operate in both I2C and SPI modes simultaneously?
A: No, the ADXL345 operates in either I2C or SPI mode, determined by the state of the CS pin. Tie CS high for I2C mode or low for SPI mode.

Q: What is the maximum cable length for I2C communication?
A: The maximum cable length depends on the pull-up resistor values and the capacitance of the I2C bus. For typical setups, keep the length under 1 meter to ensure reliable communication.

Q: How do I change the measurement range?
A: Modify the DATA_FORMAT register to set the desired range (±2g, ±4g, ±8g, or ±16g). Refer to the datasheet for specific register values.

By following this documentation, users can effectively integrate and utilize the ADXL345 in their projects.