How to Use ADXL345: Examples, Pinouts, and Specs

The ADXL345 is a small, thin, low-power, 3-axis accelerometer with a digital output. It is capable of measuring acceleration in three dimensions (X, Y, and Z axes) with high resolution (13-bit) and a wide measurement range of ±2 g, ±4 g, ±8 g, or ±16 g. The device communicates via I²C or SPI interfaces, making it versatile and easy to integrate into a variety of systems.

• Mobile devices for screen orientation and motion detection
• Wearable technology for activity tracking
• Gaming controllers for motion sensing
• Robotics for tilt and vibration measurement
• Industrial equipment for vibration monitoring
• Automotive systems for impact detection and navigation

The ADXL345 is designed for low-power operation and high performance. Below are its key technical details:

The ADXL345 is typically available in a 14-pin LGA package. Below is the pinout and description:

1. Power Supply: Connect the VDD pin to a 3.3 V power source and the GND pin to ground.
2. Communication Interface: Choose between I²C or SPI:
   • For I²C, connect the SCL and SDA pins to the corresponding I²C lines on your microcontroller.
   • For SPI, connect the SCLK, SDI, and CS pins to the SPI lines on your microcontroller.
3. Interrupts: Use the INT1 and INT2 pins to handle interrupts for specific events (e.g., free-fall detection, activity detection).
4. Pull-Up Resistors: For I²C communication, use pull-up resistors (typically 4.7 kΩ) on the SCL and SDA lines.
5. Bypass Capacitor: Place a 0.1 µF ceramic capacitor close to the VDD pin for power supply decoupling.

• Voltage Levels: Ensure the I/O voltage levels match your microcontroller's logic levels.
• Measurement Range: Configure the measurement range (±2 g, ±4 g, etc.) based on your application requirements.
• Data Rate: Set an appropriate output data rate (ODR) to balance power consumption and performance.
• Mounting: Minimize mechanical stress and vibrations during mounting to avoid measurement errors.

Below is an example of how to interface the ADXL345 with an Arduino UNO using I²C:

#include <Wire.h> // Include the Wire library for I²C communication

#define ADXL345_ADDRESS 0x53 // I²C address of the ADXL345
#define POWER_CTL 0x2D       // Power control register
#define DATA_FORMAT 0x31     // Data format register
#define DATAX0 0x32          // X-axis data register (low byte)

// Function to initialize the ADXL345
void setupADXL345() {
  Wire.begin(); // Initialize I²C communication
  Wire.beginTransmission(ADXL345_ADDRESS);
  Wire.write(POWER_CTL); // Select the power control register
  Wire.write(0x08);      // Set the device to measurement mode
  Wire.endTransmission();

  Wire.beginTransmission(ADXL345_ADDRESS);
  Wire.write(DATA_FORMAT); // Select the data format register
  Wire.write(0x01);        // Set range to ±4 g
  Wire.endTransmission();
}

void setup() {
  Serial.begin(9600); // Initialize serial communication
  setupADXL345();     // Initialize the ADXL345
}

void loop() {
  int16_t x, y, z;

  // Read X-axis data
  Wire.beginTransmission(ADXL345_ADDRESS);
  Wire.write(DATAX0); // Request starting from the X-axis low byte
  Wire.endTransmission(false);
  Wire.requestFrom(ADXL345_ADDRESS, 6); // Request 6 bytes (X, Y, Z)

  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 the acceleration values
  Serial.print("X: "); Serial.print(x);
  Serial.print(" Y: "); Serial.print(y);
  Serial.print(" Z: "); Serial.println(z);

  delay(500); // Wait for 500 ms
}

1. No Communication with the ADXL345

   • Cause: Incorrect I²C address or wiring.
   • Solution: Verify the I²C address (default is 0x53) and check all connections.

2. Incorrect or No Data Output

   • Cause: Device not in measurement mode.
   • Solution: Ensure the POWER_CTL register is set to enable measurement mode.

3. High Noise in Readings

   • Cause: Poor power supply decoupling or mechanical vibrations.
   • Solution: Add a 0.1 µF capacitor near the VDD pin and minimize external vibrations.

4. Interrupts Not Triggering

   • Cause: Interrupts not configured correctly.
   • Solution: Verify the interrupt configuration registers and ensure the INT1/INT2 pins are connected.

• Q: Can the ADXL345 operate at 5 V?
  A: No, the maximum supply voltage is 3.6 V. Use a voltage regulator or level shifter if needed.

• Q: How do I change the measurement range?
  A: Write to the DATA_FORMAT register to set the desired range (±2 g, ±4 g, etc.).

• Q: What is the maximum sampling rate?
  A: The ADXL345 supports a maximum output data rate of 3200 Hz.

• Q: Can I use both I²C and SPI simultaneously?
  A: No, you must choose one communication interface at a time.