Basics of Turning your Remote Controll Vehicle into an Autonomous System (Drone) Using an Arduino

This code example below is the same example as comes with the library, as quite simply i can’t do any better, although later in the instructable you will see the modifications that i have made in order to influence servo positions based on external conditions and to make it more applicable to my use. This example code is just a simple pass through scrip that will change the signals from the receiver in no way at all, allowing us to check the integrity of the circuit that we create and solve issues more easily. It is currently set up to control 3 signal lines (in this called: THROTTLE, STEERING and AUX) so if you require more just add them into the code with the same formatting as is used in the lines for the current signals.

Apologies for the plain text format but i don’t know how to create a code box on here 😛 copy it into the Arduino IDE for easier reading (if anyone comments on how to do this then i will edit it :-P).

Please Remember to read the comments to make it clear as to what the code does

#include <RCArduinoFastLib.h>

// MultiChannels
//
// rcarduino.blogspot.com
//
// A simple approach for reading three RC Channels using pin change interrupts
//
// See related posts –
// http://rcarduino.blogspot.co.uk/2012/01/how-to-read-rc-receiver-with.html
// http://rcarduino.blogspot.co.uk/2012/03/need-more-interrupts-to-read-more.html
// http://rcarduino.blogspot.co.uk/2012/01/can-i-control-more-than-x-servos-with.html
//
// rcarduino.blogspot.com
//

// include the pinchangeint library – see the links in the related topics section above for details
#include <PinChangeInt.h>

// Assign your channel in pins
#define THROTTLE_IN_PIN 5
#define STEERING_IN_PIN 6
#define AUX_IN_PIN 7

// Assign your channel out pins
#define THROTTLE_OUT_PIN 8
#define STEERING_OUT_PIN 9
#define AUX_OUT_PIN 10

// Assign servo indexes
#define SERVO_THROTTLE 0
#define SERVO_STEERING 1
#define SERVO_AUX 2
#define SERVO_FRAME_SPACE 3

// These bit flags are set in bUpdateFlagsShared to indicate which
// channels have new signals
#define THROTTLE_FLAG 1
#define STEERING_FLAG 2
#define AUX_FLAG 4

// holds the update flags defined above
volatile uint8_t bUpdateFlagsShared;

// shared variables are updated by the ISR and read by loop.
// In loop we immediatley take local copies so that the ISR can keep ownership of the
// shared ones. To access these in loop we first turn interrupts off with noInterrupts
// we take a copy to use in loop and the turn interrupts back on as quickly as possible
// this ensures that we are always able to receive new signals
volatile uint16_t unThrottleInShared;
volatile uint16_t unSteeringInShared;
volatile uint16_t unAuxInShared;

// These are used to record the rising edge of a pulse in the calcInput functions
// They do not need to be volatile as they are only used in the ISR. If we wanted
// to refer to these in loop and the ISR then they would need to be declared volatile
uint16_t unThrottleInStart;
uint16_t unSteeringInStart;
uint16_t unAuxInStart;

uint16_t unLastAuxIn = 0;
uint32_t ulVariance = 0;
uint32_t ulGetNextSampleMillis = 0;
uint16_t unMaxDifference = 0;

void setup()
{
Serial.begin(115200);
Serial.println(“multiChannels”);

// attach servo objects, these will generate the correct
// pulses for driving Electronic speed controllers, servos or other devices
// designed to interface directly with RC Receivers
CRCArduinoFastServos::attach(SERVO_THROTTLE,THROTTLE_OUT_PIN);
CRCArduinoFastServos::attach(SERVO_STEERING,STEERING_OUT_PIN);
CRCArduinoFastServos::attach(SERVO_AUX,AUX_OUT_PIN);

// lets set a standard rate of 50 Hz by setting a frame space of 10 * 2000 = 3 Servos + 7 times 2000
CRCArduinoFastServos::setFrameSpaceA(SERVO_FRAME_SPACE,7*2000);
CRCArduinoFastServos::begin();

// using the PinChangeInt library, attach the interrupts used to read the channels
PCintPort::attachInterrupt(THROTTLE_IN_PIN, calcThrottle,CHANGE);
PCintPort::attachInterrupt(STEERING_IN_PIN, calcSteering,CHANGE);
PCintPort::attachInterrupt(AUX_IN_PIN, calcAux,CHANGE);
}

void loop()
{
// create local variables to hold a local copies of the channel inputs
// these are declared static so that thier values will be retained between calls to loop.
static uint16_t unThrottleIn;
static uint16_t unSteeringIn;
static uint16_t unAuxIn;
// local copy of update flags
static uint8_t bUpdateFlags;

// check shared update flags to see if any channels have a new signal
if(bUpdateFlagsShared)
{
noInterrupts(); // turn interrupts off quickly while we take local copies of the shared variables

// take a local copy of which channels were updated in case we need to use this in the rest of loop
bUpdateFlags = bUpdateFlagsShared;

// in the current code, the shared values are always populated
// so we could copy them without testing the flags
// however in the future this could change, so lets
// only copy when the flags tell us we can.
if(bUpdateFlags & THROTTLE_FLAG)
{
unThrottleIn = unThrottleInShared;
}
if(bUpdateFlags & STEERING_FLAG)
{
unSteeringIn = unSteeringInShared;
}
if(bUpdateFlags & AUX_FLAG)
{
unAuxIn = unAuxInShared;
}

// clear shared copy of updated flags as we have already taken the updates
// we still have a local copy if we need to use it in bUpdateFlags
bUpdateFlagsShared = 0;

interrupts(); // we have local copies of the inputs, so now we can turn interrupts back on
// as soon as interrupts are back on, we can no longer use the shared copies, the interrupt
// service routines own these and could update them at any time. During the update, the
// shared copies may contain junk. Luckily we have our local copies to work with 🙂
}

// do any processing from here onwards
// only use the local values unAuxIn, unThrottleIn and unSteeringIn, the shared
// variables unAuxInShared, unThrottleInShared, unSteeringInShared are always owned by
// the interrupt routines and should not be used in loop

// the following code provides simple pass through this is a good initial test
// the Arduino will pass through receiver input as if the Arduino is not there.
// This should be used to confirm the circuit and power
// before attempting any custom processing in a project.

// we are checking to see if the channel value has changed, this is indicated
// by the flags. For the simple pass through we don’t really need this check,
// but for a more complex project where a new signal requires significant processing
// this allows us to only calculate new values when we have new inputs, rather than
// on every cycle.
if(bUpdateFlags & THROTTLE_FLAG)
{
CRCArduinoFastServos::writeMicroseconds(SERVO_THROTTLE,unThrottleIn);
}

if(bUpdateFlags & STEERING_FLAG)
{
CRCArduinoFastServos::writeMicroseconds(SERVO_STEERING,unSteeringIn);
}

if(bUpdateFlags & AUX_FLAG)
{
CRCArduinoFastServos::writeMicroseconds(SERVO_AUX,unAuxIn);
}

bUpdateFlags = 0;
}

// simple interrupt service routine
void calcThrottle()
{
if(PCintPort::pinState)
{
unThrottleInStart = TCNT1;
}
else
{
unThrottleInShared = (TCNT1 – unThrottleInStart)>>1;
bUpdateFlagsShared |= THROTTLE_FLAG;
}
}

void calcSteering()
{
if(PCintPort::pinState)
{
unSteeringInStart = TCNT1;
}
else
{
unSteeringInShared = (TCNT1 – unSteeringInStart)>>1;

bUpdateFlagsShared |= STEERING_FLAG;
}
}

void calcAux()
{
if(PCintPort::pinState)
{
unAuxInStart = TCNT1;
}
else
{
unAuxInShared = (TCNT1 – unAuxInStart)>>1;
bUpdateFlagsShared |= AUX_FLAG;  }
}