Notes

#include "mbed.h"
#include "ADXL345_I2C.h"

// Define the I2C pins for the ADXL345
// Assuming PB_11 is SDA and PB_10 is SCL based on the code snippet
ADXL345_I2C accelerometer(PB_11, PB_10);

// Global variables for raw and filtered output
int X_OUT_raw, Y_OUT_raw, Z_OUT_raw; // Inputs/Raw Data
int X_OUT, Y_OUT, Z_OUT; // Outputs/Filtered Data

int main() {
// Array to hold the initial raw readings (used in the snippet, typically for offsets or setup)
int readings[3] = {0, 0, 0};

// Setup serial communication for printing to PC
// Default mbed setup for Serial/USB
Serial pc(USBTX, USBRX);

pc.printf("Starting ADXL345 Test...n");
wait(0.001);

// Read and print the device ID (should be 0x2D for ADXL345)
pc.printf("Device ID is: 0x%2Xn", accelerometer.getDeviceID());
wait(0.001);

// --- Initialization and Configuration ---

// Set power control to a state where the device is not initialized/in standby (0x00)
if (accelerometer.setPowerControl(0x00)) {
pc.printf("Didn't intitialize power controln");
return 0;
}
wait(0.001);

// Set full resolution and 4mg/Lsb
// The constant 0x0B likely corresponds to a setting for Full Resolution (and range)
if (accelerometer.setDataFormatControl(0x0B)) {
pc.printf("didn't set data formatn");
return 0;
}
wait(0.001);

// Set data rate to 3200 Hz (ADXL345_3200HZ is likely a defined constant)
// The snippet mentions "3.2kHz data rate"
if (accelerometer.setDataRate(ADXL345_3200HZ)) {
pc.printf("didn't set data raten");
return 0;
}
wait(0.001);

// Set power control to Measurement Mode (ADXL345 is actively measuring)
// MeasurementMode is likely a defined constant (e.g., 0x08)
if (accelerometer.setPowerControl(MeasurementMode)) {
pc.printf("didn't set the power control to measurementn");
return 0;
}

// --- Main Loop for Reading and Filtering ---
while (1) {
wait(0.1); // Wait for 100ms before next reading

// Read the acceleration values from the sensor
accelerometer.getOutput(readings);
wait(0.1);

// Map the array readings back to individual raw variables
X_OUT_raw = (int16_t)readings[0];
Y_OUT_raw = (int16_t)readings[1];
Z_OUT_raw = (int16_t)readings[2];

// --- Low Pass Filter (FIR/IIR) Implementation ---

// This is a simple first-order IIR (Infinite Impulse Response) or
// Exponential Moving Average (EMA) filter.
// It's a common technique for smoothing sensor data.
// New Value = (1 - alpha) * Old Value + alpha * Raw Value
// Here, alpha = 0.06 and (1 - alpha) = 0.94

// Low pass filter for stable X,Y,Z values
X_OUT = 0.94 * X_OUT + 0.06 * X_OUT_raw;
Y_OUT = 0.94 * Y_OUT + 0.06 * Y_OUT_raw;
Z_OUT = 0.94 * Z_OUT + 0.06 * Z_OUT_raw;

// Print the filtered (and raw) values to the PC
// rn ensures a new line and carriage return
// Note: The format specifier %i is used for integers.
pc.printf("X_i,%i,X_i\r\n", X_OUT, Y_OUT, Z_OUT);
}
}