/**
* The software is provided "as is", without any warranty of any kind.
* Feel free to edit it if needed.
*
* @author lobodol <[email protected]>
*/
// ---------------------------------------------------------------------------
#include <Wire.h>
// ------------------- Define some constants for convenience -----------------
#define CHANNEL1 0
#define CHANNEL2 1
#define CHANNEL3 2
#define CHANNEL4 3
#define YAW 0
#define PITCH 1
#define ROLL 2
#define THROTTLE 3
#define X 0 // X axis
#define Y 1 // Y axis
#define Z 2 // Z axis
#define MPU_ADDRESS 0x68 // I2C address of the MPU-6050
#define FREQ 250 // Sampling frequency
#define SSF_GYRO 65.5 // Sensitivity Scale Factor of the gyro from datasheet
#define STOPPED 0
#define STARTING 1
#define STARTED 2
// ---------------- Receiver variables ---------------------------------------
// Previous state of each channel (HIGH or LOW)
volatile byte previous_state[4];
// Duration of the pulse on each channel of the receiver in µs (must be within 1000µs & 2000µs)
volatile unsigned int pulse_length[4] = {1500, 1500, 1000, 1500};
// Used to calculate pulse duration on each channel
volatile unsigned long current_time;
volatile unsigned long timer[4]; // Timer of each channel
// Used to configure which control (yaw, pitch, roll, throttle) is on which channel
int mode_mapping[4];
// ----------------------- MPU variables -------------------------------------
// The RAW values got from gyro (in °/sec) in that order: X, Y, Z
int gyro_raw[3] = {0,0,0};
// Average gyro offsets of each axis in that order: X, Y, Z
long gyro_offset[3] = {0, 0, 0};
// Calculated angles from gyro's values in that order: X, Y, Z
float gyro_angle[3] = {0,0,0};
// The RAW values got from accelerometer (in m/sec²) in that order: X, Y, Z
int acc_raw[3] = {0 ,0 ,0};
// Calculated angles from accelerometer's values in that order: X, Y, Z
float acc_angle[3] = {0,0,0};
// Total 3D acceleration vector in m/s²
long acc_total_vector;
// Calculated angular motion on each axis: Yaw, Pitch, Roll
float angular_motions[3] = {0, 0, 0};
/**
* Real measures on 3 axis calculated from gyro AND accelerometer in that order : Yaw, Pitch, Roll
* - Left wing up implies a positive roll
* - Nose up implies a positive pitch
* - Nose right implies a positive yaw
*/
float measures[3] = {0, 0, 0};
// MPU's temperature
int temperature;
// Init flag set to TRUE after first loop
boolean initialized;
// ----------------------- Variables for servo signal generation -------------
unsigned int period; // Sampling period
unsigned long loop_timer;
unsigned long now, difference;
unsigned long pulse_length_esc1 = 1000,
pulse_length_esc2 = 1000,
pulse_length_esc3 = 1000,
pulse_length_esc4 = 1000;
// ------------- Global variables used for PID controller --------------------
float pid_set_points[3] = {0, 0, 0}; // Yaw, Pitch, Roll
// Errors
float errors[3]; // Measured errors (compared to instructions) : [Yaw, Pitch, Roll]
float delta_err[3] = {0, 0, 0}; // Error deltas in that order : Yaw, Pitch, Roll
float error_sum[3] = {0, 0, 0}; // Error sums (used for integral component) : [Yaw, Pitch, Roll]
float previous_error[3] = {0, 0, 0}; // Last errors (used for derivative component) : [Yaw, Pitch, Roll]
// PID coefficients
float Kp[3] = {4.0, 1.3, 1.3}; // P coefficients in that order : Yaw, Pitch, Roll
float Ki[3] = {0.02, 0.04, 0.04}; // I coefficients in that order : Yaw, Pitch, Roll
float Kd[3] = {0, 18, 18}; // D coefficients in that order : Yaw, Pitch, Roll
// ---------------------------------------------------------------------------
/**
* Status of the quadcopter:
* - 0 : stopped
* - 1 : starting
* - 2 : started
*
* @var int
*/
int status = STOPPED;
// ---------------------------------------------------------------------------
int battery_voltage;
// ---------------------------------------------------------------------------
/**
* Setup configuration
*/
void setup() {
// Start I2C communication
Wire.begin();
TWBR = 12; // Set the I2C clock speed to 400kHz.
// Turn LED on during setup
pinMode(13, OUTPUT);
digitalWrite(13, HIGH);
// Set pins #4 #5 #6 #7 as outputs
DDRD |= B11110000;
/**
setupMpu6050Registers();
calibrateMpu6050();
configureChannelMapping();
// Configure interrupts for receiver
PCICR |= (1 << PCIE0); // Set PCIE0 to enable PCMSK0 scan
PCMSK0 |= (1 << PCINT0); // Set PCINT0 (digital input 8) to trigger an interrupt on state change
PCMSK0 |= (1 << PCINT1); // Set PCINT1 (digital input 9) to trigger an interrupt on state change
PCMSK0 |= (1 << PCINT2); // Set PCINT2 (digital input 10)to trigger an interrupt on state change
PCMSK0 |= (1 << PCINT3); // Set PCINT3 (digital input 11)to trigger an interrupt on state change
period = (1000000/FREQ) ; // Sampling period in µs
**/
// Initialize loop_timer
loop_timer = micros();
// Turn LED off now setup is done
digitalWrite(13, LOW);
}
/**
* Main program loop
*/
void loop() {
// 1. First, read raw values from MPU-6050
// readSensor();
// 2. Calculate angles from gyro & accelerometer's values
// calculateAngles();
// 3. Calculate set points of PID controller
// calculateSetPoints();
// 4. Calculate errors comparing angular motions to set points
// calculateErrors();
/** if (isStarted()) {
// 5. Calculate motors speed with PID controller
pidController();
compensateBatteryDrop();
}
**/
// 6. Apply motors speed
applyMotorSpeed();
pulse_length_esc1 = 450+random(2000);
}
/**
* Generate servo-signal on digital pins #4 #5 #6 #7 with a frequency of 250Hz (4ms period).
* Direct port manipulation is used for performances.
*
* This function might not take more than 2ms to run, which lets 2ms remaining to do other stuff.
*
* @see https:// www.arduino.cc/en/Reference/PortManipulation
*/
void applyMotorSpeed() {
// Refresh rate is 250Hz: send ESC pulses every 4000µs
while ((now = micros()) - loop_timer < period);
// Update loop timer
loop_timer = now;
// Set pins #4 #5 #6 #7 HIGH
PORTD |= B11110000;
// Wait until all pins #4 #5 #6 #7 are LOW
while (PORTD >= 16) {
now = micros();
difference = now - loop_timer;
if (difference >= pulse_length_esc1) PORTD &= B11101111; // Set pin #4 LOW
if (difference >= pulse_length_esc2) PORTD &= B11011111; // Set pin #5 LOW
if (difference >= pulse_length_esc3) PORTD &= B10111111; // Set pin #6 LOW
if (difference >= pulse_length_esc4) PORTD &= B01111111; // Set pin #7 LOW
}
}
/**
* Request raw values from MPU6050.
*/
void readSensor() {
Wire.beginTransmission(MPU_ADDRESS); // Start communicating with the MPU-6050
Wire.write(0x3B); // Send the requested starting register
Wire.endTransmission(); // End the transmission
Wire.requestFrom(MPU_ADDRESS,14); // Request 14 bytes from the MPU-6050
// Wait until all the bytes are received
while(Wire.available() < 14);
acc_raw[X] = Wire.read() << 8 | Wire.read(); // Add the low and high byte to the acc_raw[X] variable
acc_raw[Y] = Wire.read() << 8 | Wire.read(); // Add the low and high byte to the acc_raw[Y] variable
acc_raw[Z] = Wire.read() << 8 | Wire.read(); // Add the low and high byte to the acc_raw[Z] variable
temperature = Wire.read() << 8 | Wire.read(); // Add the low and high byte to the temperature variable
gyro_raw[X] = Wire.read() << 8 | Wire.read(); // Add the low and high byte to the gyro_raw[X] variable
gyro_raw[Y] = Wire.read() << 8 | Wire.read(); // Add the low and high byte to the gyro_raw[Y] variable
gyro_raw[Z] = Wire.read() << 8 | Wire.read(); // Add the low and high byte to the gyro_raw[Z] variable
}
/**
* Calculate real angles from gyro and accelerometer's values
*/
void calculateAngles() {
calculateGyroAngles();
calculateAccelerometerAngles();
if (initialized) {
// Correct the drift of the gyro with the accelerometer
gyro_angle[X] = gyro_angle[X] * 0.9996 + acc_angle[X] * 0.0004;
gyro_angle[Y] = gyro_angle[Y] * 0.9996 + acc_angle[Y] * 0.0004;
} else {
// At very first start, init gyro angles with accelerometer angles
resetGyroAngles();
initialized = true;
}
// To dampen the pitch and roll angles a complementary filter is used
measures[ROLL] = measures[ROLL] * 0.9 + gyro_angle[X] * 0.1;
measures[PITCH] = measures[PITCH] * 0.9 + gyro_angle[Y] * 0.1;
measures[YAW] = -gyro_raw[Z] / SSF_GYRO; // Store the angular motion for this axis
// Apply low-pass filter (10Hz cutoff frequency)
angular_motions[ROLL] = 0.7 * angular_motions[ROLL] + 0.3 * gyro_raw[X] / SSF_GYRO;
angular_motions[PITCH] = 0.7 * angular_motions[PITCH] + 0.3 * gyro_raw[Y] / SSF_GYRO;
angular_motions[YAW] = 0.7 * angular_motions[YAW] + 0.3 * gyro_raw[Z] / SSF_GYRO;
}
/**
* Calculate pitch & roll angles using only the gyro.
*/
void calculateGyroAngles() {
// Subtract offsets
gyro_raw[X] -= gyro_offset[X];
gyro_raw[Y] -= gyro_offset[Y];
gyro_raw[Z] -= gyro_offset[Z];
// Angle calculation using integration
gyro_angle[X] += (gyro_raw[X] / (FREQ * SSF_GYRO));
gyro_angle[Y] += (-gyro_raw[Y] / (FREQ * SSF_GYRO)); // Change sign to match the accelerometer's one
// Transfer roll to pitch if IMU has yawed
gyro_angle[Y] += gyro_angle[X] * sin(gyro_raw[Z] * (PI / (FREQ * SSF_GYRO * 180)));
gyro_angle[X] -= gyro_angle[Y] * sin(gyro_raw[Z] * (PI / (FREQ * SSF_GYRO * 180)));
}
/**
* Calculate pitch & roll angles using only the accelerometer.
*/
void calculateAccelerometerAngles() {
// Calculate total 3D acceleration vector : √(X² + Y² + Z²)
acc_total_vector = sqrt(pow(acc_raw[X], 2) + pow(acc_raw[Y], 2) + pow(acc_raw[Z], 2));
// To prevent asin to produce a NaN, make sure the input value is within [-1;+1]
if (abs(acc_raw[X]) < acc_total_vector) {
acc_angle[X] = asin((float)acc_raw[Y] / acc_total_vector) * (180 / PI); // asin gives angle in radian. Convert to degree multiplying by 180/pi
}
if (abs(acc_raw[Y]) < acc_total_vector) {
acc_angle[Y] = asin((float)acc_raw[X] / acc_total_vector) * (180 / PI);
}
}
/**
* Calculate motor speed for each motor of an X quadcopter depending on received instructions and measures from sensor
* by applying PID control.
*
* (A) (B) x
* \ / z ↑
* X \|
* / \ +----→ y
* (C) (D)
*
* Motors A & D run clockwise.
* Motors B & C run counter-clockwise.
*
* Each motor output is considered as a servomotor. As a result, value range is about 1000µs to 2000µs
*/
void pidController() {
float yaw_pid = 0;
float pitch_pid = 0;
float roll_pid = 0;
int throttle = pulse_length[mode_mapping[THROTTLE]];
// Initialize motor commands with throttle
pulse_length_esc1 = throttle;
pulse_length_esc2 = throttle;
pulse_length_esc3 = throttle;
pulse_length_esc4 = throttle;
// Do not calculate anything if throttle is 0
if (throttle >= 1012) {
// PID = e.Kp + ∫e.Ki + Δe.Kd
yaw_pid = (errors[YAW] * Kp[YAW]) + (error_sum[YAW] * Ki[YAW]) + (delta_err[YAW] * Kd[YAW]);
pitch_pid = (errors[PITCH] * Kp[PITCH]) + (error_sum[PITCH] * Ki[PITCH]) + (delta_err[PITCH] * Kd[PITCH]);
roll_pid = (errors[ROLL] * Kp[ROLL]) + (error_sum[ROLL] * Ki[ROLL]) + (delta_err[ROLL] * Kd[ROLL]);
// Keep values within acceptable range. TODO export hard-coded values in variables/const
yaw_pid = minMax(yaw_pid, -400, 400);
pitch_pid = minMax(pitch_pid, -400, 400);
roll_pid = minMax(roll_pid, -400, 400);
// Calculate pulse duration for each ESC
pulse_length_esc1 = throttle - roll_pid - pitch_pid + yaw_pid;
pulse_length_esc2 = throttle + roll_pid - pitch_pid - yaw_pid;
pulse_length_esc3 = throttle - roll_pid + pitch_pid - yaw_pid;
pulse_length_esc4 = throttle + roll_pid + pitch_pid + yaw_pid;
}
// Prevent out-of-range-values
pulse_length_esc1 = minMax(pulse_length_esc1, 1100, 2000);
pulse_length_esc2 = minMax(pulse_length_esc2, 1100, 2000);
pulse_length_esc3 = minMax(pulse_length_esc3, 1100, 2000);
pulse_length_esc4 = minMax(pulse_length_esc4, 1100, 2000);
}
/**
* Calculate errors used by PID controller
*/
void calculateErrors() {
// Calculate current errors
errors[YAW] = angular_motions[YAW] - pid_set_points[YAW];
errors[PITCH] = angular_motions[PITCH] - pid_set_points[PITCH];
errors[ROLL] = angular_motions[ROLL] - pid_set_points[ROLL];
// Calculate sum of errors : Integral coefficients
error_sum[YAW] += errors[YAW];
error_sum[PITCH] += errors[PITCH];
error_sum[ROLL] += errors[ROLL];
// Keep values in acceptable range
error_sum[YAW] = minMax(error_sum[YAW], -400/Ki[YAW], 400/Ki[YAW]);
error_sum[PITCH] = minMax(error_sum[PITCH], -400/Ki[PITCH], 400/Ki[PITCH]);
error_sum[ROLL] = minMax(error_sum[ROLL], -400/Ki[ROLL], 400/Ki[ROLL]);
// Calculate error delta : Derivative coefficients
delta_err[YAW] = errors[YAW] - previous_error[YAW];
delta_err[PITCH] = errors[PITCH] - previous_error[PITCH];
delta_err[ROLL] = errors[ROLL] - previous_error[ROLL];
// Save current error as previous_error for next time
previous_error[YAW] = errors[YAW];
previous_error[PITCH] = errors[PITCH];
previous_error[ROLL] = errors[ROLL];
}
/**
* Customize mapping of controls: set here which command is on which channel and call
* this function in setup() routine.
*/
void configureChannelMapping() {
mode_mapping[YAW] = CHANNEL4;
mode_mapping[PITCH] = CHANNEL2;
mode_mapping[ROLL] = CHANNEL1;
mode_mapping[THROTTLE] = CHANNEL3;
}
/**
* Configure gyro and accelerometer precision as following:
* - accelerometer: ±8g
* - gyro: ±500°/s
*
* @see https://www.invensense.com/wp-content/uploads/2015/02/MPU-6000-Register-Map1.pdf
*/
void setupMpu6050Registers() {
// Configure power management
Wire.beginTransmission(MPU_ADDRESS); // Start communication with MPU
Wire.write(0x6B); // Request the PWR_MGMT_1 register
Wire.write(0x00); // Apply the desired configuration to the register
Wire.endTransmission(); // End the transmission
// Configure the gyro's sensitivity
Wire.beginTransmission(MPU_ADDRESS); // Start communication with MPU
Wire.write(0x1B); // Request the GYRO_CONFIG register
Wire.write(0x08); // Apply the desired configuration to the register : ±500°/s
Wire.endTransmission(); // End the transmission
// Configure the acceleromter's sensitivity
Wire.beginTransmission(MPU_ADDRESS); // Start communication with MPU
Wire.write(0x1C); // Request the ACCEL_CONFIG register
Wire.write(0x10); // Apply the desired configuration to the register : ±8g
Wire.endTransmission(); // End the transmission
// Configure low pass filter
Wire.beginTransmission(MPU_ADDRESS); // Start communication with MPU
Wire.write(0x1A); // Request the CONFIG register
Wire.write(0x03); // Set Digital Low Pass Filter about ~43Hz
Wire.endTransmission(); // End the transmission
}
/**
* Calibrate MPU6050: take 2000 samples to calculate average offsets.
* During this step, the quadcopter needs to be static and on a horizontal surface.
*
* This function also sends low throttle signal to each ESC to init and prevent them beeping annoyingly.
*
* This function might take ~2sec for 2000 samples.
*/
void calibrateMpu6050() {
int max_samples = 2000;
for (int i = 0; i < max_samples; i++) {
readSensor();
gyro_offset[X] += gyro_raw[X];
gyro_offset[Y] += gyro_raw[Y];
gyro_offset[Z] += gyro_raw[Z];
// Generate low throttle pulse to init ESC and prevent them beeping
PORTD |= B11110000; // Set pins #4 #5 #6 #7 HIGH
delayMicroseconds(1000); // Wait 1000µs
PORTD &= B00001111; // Then set LOW
// Just wait a bit before next loop
delay(3);
}
// Calculate average offsets
gyro_offset[X] /= max_samples;
gyro_offset[Y] /= max_samples;
gyro_offset[Z] /= max_samples;
}
/**
* Make sure that given value is not over min_value/max_value range.
*
* @param float value : The value to convert
* @param float min_value : The min value
* @param float max_value : The max value
*
* @return float
*/
float minMax(float value, float min_value, float max_value) {
if (value > max_value) {
value = max_value;
} else if (value < min_value) {
value = min_value;
}
return value;
}
/**
* Return whether the quadcopter is started.
* To start the quadcopter, move the left stick in bottom left corner then, move it back in center position.
* To stop the quadcopter move the left stick in bottom right corner.
*
* @return bool
*/
bool isStarted() {
// When left stick is moved in the bottom left corner
if (status == STOPPED && pulse_length[mode_mapping[YAW]] <= 1012 && pulse_length[mode_mapping[THROTTLE]] <= 1012) {
status = STARTING;
}
// When left stick is moved back in the center position
if (status == STARTING && pulse_length[mode_mapping[YAW]] == 1500 && pulse_length[mode_mapping[THROTTLE]] <= 1012) {
status = STARTED;
// Reset PID controller's variables to prevent bump start
resetPidController();
resetGyroAngles();
}
// When left stick is moved in the bottom right corner
if (status == STARTED && pulse_length[mode_mapping[YAW]] >= 1988 && pulse_length[mode_mapping[THROTTLE]] <= 1012) {
status = STOPPED;
// Make sure to always stop motors when status is STOPPED
stopAll();
}
return status == STARTED;
}
/**
* Reset gyro's angles with accelerometer's angles.
*/
void resetGyroAngles() {
gyro_angle[X] = acc_angle[X];
gyro_angle[Y] = acc_angle[Y];
}
/**
* Reset motors' pulse length to 1000µs to totally stop them.
*/
void stopAll() {
pulse_length_esc1 = 1000;
pulse_length_esc2 = 1000;
pulse_length_esc3 = 1000;
pulse_length_esc4 = 1000;
}
/**
* Reset all PID controller's variables.
*/
void resetPidController() {
errors[YAW] = 0;
errors[PITCH] = 0;
errors[ROLL] = 0;
error_sum[YAW] = 0;
error_sum[PITCH] = 0;
error_sum[ROLL] = 0;
previous_error[YAW] = 0;
previous_error[PITCH] = 0;
previous_error[ROLL] = 0;
}
/**
* Calculate PID set points on axis YAW, PITCH, ROLL
*/
void calculateSetPoints() {
pid_set_points[YAW] = calculateYawSetPoint(pulse_length[mode_mapping[YAW]], pulse_length[mode_mapping[THROTTLE]]);
pid_set_points[PITCH] = calculateSetPoint(measures[PITCH], pulse_length[mode_mapping[PITCH]]);
pid_set_points[ROLL] = calculateSetPoint(measures[ROLL], pulse_length[mode_mapping[ROLL]]);
}
/**
* Calculate the PID set point in °/s
*
* @param float angle Measured angle (in °) on an axis
* @param int channel_pulse Pulse length of the corresponding receiver channel
* @return float
*/
float calculateSetPoint(float angle, int channel_pulse) {
float level_adjust = angle * 15; // Value 15 limits maximum angle value to ±32.8°
float set_point = 0;
// Need a dead band of 16µs for better result
if (channel_pulse > 1508) {
set_point = channel_pulse - 1508;
} else if (channel_pulse < 1492) {
set_point = channel_pulse - 1492;
}
set_point -= level_adjust;
set_point /= 3;
return set_point;
}
/**
* Calculate the PID set point of YAW axis in °/s
*
* @param int yaw_pulse Receiver pulse length of yaw's channel
* @param int throttle_pulse Receiver pulse length of throttle's channel
* @return float
*/
float calculateYawSetPoint(int yaw_pulse, int throttle_pulse) {
float set_point = 0;
// Do not yaw when turning off the motors
if (throttle_pulse > 1050) {
// There is no notion of angle on this axis as the quadcopter can turn on itself
set_point = calculateSetPoint(0, yaw_pulse);
}
return set_point;
}
/**
* Compensate battery drop applying a coefficient on output values
*/
void compensateBatteryDrop() {
if (isBatteryConnected()) {
pulse_length_esc1 += pulse_length_esc1 * ((1240 - battery_voltage) / (float) 3500);
pulse_length_esc2 += pulse_length_esc2 * ((1240 - battery_voltage) / (float) 3500);
pulse_length_esc3 += pulse_length_esc3 * ((1240 - battery_voltage) / (float) 3500);
pulse_length_esc4 += pulse_length_esc4 * ((1240 - battery_voltage) / (float) 3500);
}
}
/**
* Read battery voltage & return whether the battery seems connected
*
* @return boolean
*/
bool isBatteryConnected() {
// Reduce noise with a low-pass filter (10Hz cutoff frequency)
battery_voltage = battery_voltage * 0.92 + (analogRead(0) + 65) * 0.09853;
return battery_voltage < 1240 && battery_voltage > 800;
}
/**
* This Interrupt Sub Routine is called each time input 8, 9, 10 or 11 changed state.
* Read the receiver signals in order to get flight instructions.
*
* This routine must be as fast as possible to prevent main program to be messed up.
* The trick here is to use port registers to read pin state.
* Doing (PINB & B00000001) is the same as digitalRead(8) with the advantage of using less CPU loops.
* It is less convenient but more efficient, which is the most important here.
*
* @see https://www.arduino.cc/en/Reference/PortManipulation
* @see https://www.firediy.fr/article/utiliser-sa-radiocommande-avec-un-arduino-drone-ch-6
*/
ISR(PCINT0_vect) {
current_time = micros();
// Channel 1 -------------------------------------------------
if (PINB & B00000001) { // Is input 8 high ?
if (previous_state[CHANNEL1] == LOW) { // Input 8 changed from 0 to 1 (rising edge)
previous_state[CHANNEL1] = HIGH; // Save current state
timer[CHANNEL1] = current_time; // Save current time
}
} else if (previous_state[CHANNEL1] == HIGH) { // Input 8 changed from 1 to 0 (falling edge)
previous_state[CHANNEL1] = LOW; // Save current state
pulse_length[CHANNEL1] = current_time - timer[CHANNEL1]; // Calculate pulse duration & save it
}
// Channel 2 -------------------------------------------------
if (PINB & B00000010) { // Is input 9 high ?
if (previous_state[CHANNEL2] == LOW) { // Input 9 changed from 0 to 1 (rising edge)
previous_state[CHANNEL2] = HIGH; // Save current state
timer[CHANNEL2] = current_time; // Save current time
}
} else if (previous_state[CHANNEL2] == HIGH) { // Input 9 changed from 1 to 0 (falling edge)
previous_state[CHANNEL2] = LOW; // Save current state
pulse_length[CHANNEL2] = current_time - timer[CHANNEL2]; // Calculate pulse duration & save it
}
// Channel 3 -------------------------------------------------
if (PINB & B00000100) { // Is input 10 high ?
if (previous_state[CHANNEL3] == LOW) { // Input 10 changed from 0 to 1 (rising edge)
previous_state[CHANNEL3] = HIGH; // Save current state
timer[CHANNEL3] = current_time; // Save current time
}
} else if (previous_state[CHANNEL3] == HIGH) { // Input 10 changed from 1 to 0 (falling edge)
previous_state[CHANNEL3] = LOW; // Save current state
pulse_length[CHANNEL3] = current_time - timer[CHANNEL3]; // Calculate pulse duration & save it
}
// Channel 4 -------------------------------------------------
if (PINB & B00001000) { // Is input 11 high ?
if (previous_state[CHANNEL4] == LOW) { // Input 11 changed from 0 to 1 (rising edge)
previous_state[CHANNEL4] = HIGH; // Save current state
timer[CHANNEL4] = current_time; // Save current time
}
} else if (previous_state[CHANNEL4] == HIGH) { // Input 11 changed from 1 to 0 (falling edge)
previous_state[CHANNEL4] = LOW; // Save current state
pulse_length[CHANNEL4] = current_time - timer[CHANNEL4]; // Calculate pulse duration & save it
}
}