Reading RC Channels with Arduino Due

Update 27/04/2013

The following code was originally presented as a test sketch to demonstrate a glitch in the Arduino Due micros function which is being resolved. See the following post for details of the glitch and resolution.

http://arduino.cc/forum/index.php/topic,162787.0/topicseen.html

With this resolution in place the code presented below can be used to read 8 RC Channels and output them to a combination of upto 8 RC Servos or ESCs.

The code can be operated in two configurations -

1) Loop Back Test - Here 8 servo outputs are created and given fixed values from 1100 to 1800, these pulse values are output on pins 10 to 17 and can be read back in through the interrupts attached to pins 2 to 9. This is intended to give the user confidence that the code is able to read multiple RC Channels before moving to configuration 2 - Pass Through

2) Pass Through -  This is similar to 1) above however the input is now connected to the output such that a change in an incoming signal will cause a corresponding change in the servo output signal. To implement pass  through on any channel, simply remove the comment form the start of the servo.writeMicrosecond command for that channel for example

Change this -

  if(bUpdateFlags & CHANNEL1_FLAG)
  {
      // remove the // from the line below to implement pass through updates to the servo on this channel -
      //servoChannel1.writeMicroseconds(unChannel1In);
      Serial.print(unChannel1In);
      Serial.print(",");
  }
to this -

  if(bUpdateFlags & CHANNEL1_FLAG)
  {
      // remove the // from the line below to implement pass through updates to the servo on this channel -
      servoChannel1.writeMicroseconds(unChannel1In);
      Serial.print(unChannel1In);
      Serial.print(",");
  }




The code has been ported from an original project based on the Arduino UNO, follow the links in the comments for the background and detailed explanation.

// MultiChannels
//
// rcarduino.blogspot.com
//
// A simple approach for reading and writing eight RC Channels using Arduino Due 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 "Servo.h"

// Assign your channel in pins
#define CHANNEL1_IN_PIN 2
#define CHANNEL2_IN_PIN 3
#define CHANNEL3_IN_PIN 4
#define CHANNEL4_IN_PIN 5
#define CHANNEL5_IN_PIN 6
#define CHANNEL6_IN_PIN 7
#define CHANNEL7_IN_PIN 8
#define CHANNEL8_IN_PIN 9

// Assign your channel out pins
#define CHANNEL1_OUT_PIN 10
#define CHANNEL2_OUT_PIN 11
#define CHANNEL3_OUT_PIN 12
#define CHANNEL4_OUT_PIN 13
#define CHANNEL5_OUT_PIN 14
#define CHANNEL6_OUT_PIN 15
#define CHANNEL7_OUT_PIN 16
#define CHANNEL8_OUT_PIN 17

// Servo objects generate the signals expected by Electronic Speed Controllers and Servos
// We will use the objects to output the signals we read in
// this example code provides a straight pass through of the signal with no custom processing
Servo servoChannel1;
Servo servoChannel2;
Servo servoChannel3;
Servo servoChannel4;
Servo servoChannel5;
Servo servoChannel6;
Servo servoChannel7;
Servo servoChannel8;

// These bit flags are set in bUpdateFlagsShared to indicate which
// channels have new signals
#define CHANNEL1_FLAG 1
#define CHANNEL2_FLAG 2
#define CHANNEL3_FLAG 4
#define CHANNEL4_FLAG 8
#define CHANNEL5_FLAG 16
#define CHANNEL6_FLAG 32
#define CHANNEL7_FLAG 64
#define CHANNEL8_FLAG 128

// holds the update flags defined above
volatile uint32_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 uint32_t unChannel1InShared;
volatile uint32_t unChannel2InShared;
volatile uint32_t unChannel3InShared;
volatile uint32_t unChannel4InShared;
volatile uint32_t unChannel5InShared;
volatile uint32_t unChannel6InShared;
volatile uint32_t unChannel7InShared;
volatile uint32_t unChannel8InShared;

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
  servoChannel1.attach(CHANNEL1_OUT_PIN);
  servoChannel2.attach(CHANNEL2_OUT_PIN);
  servoChannel3.attach(CHANNEL3_OUT_PIN);
  servoChannel4.attach(CHANNEL4_OUT_PIN);
  servoChannel5.attach(CHANNEL5_OUT_PIN);
  servoChannel6.attach(CHANNEL6_OUT_PIN);
  servoChannel7.attach(CHANNEL7_OUT_PIN);
  servoChannel8.attach(CHANNEL8_OUT_PIN);

  // attach the interrupts used to read the channels
  attachInterrupt(CHANNEL1_IN_PIN, calcChannel1,CHANGE);
  attachInterrupt(CHANNEL2_IN_PIN, calcChannel2,CHANGE);
  attachInterrupt(CHANNEL3_IN_PIN, calcChannel3,CHANGE);
  attachInterrupt(CHANNEL4_IN_PIN, calcChannel4,CHANGE);
  attachInterrupt(CHANNEL5_IN_PIN, calcChannel5,CHANGE);
  attachInterrupt(CHANNEL6_IN_PIN, calcChannel6,CHANGE);
  attachInterrupt(CHANNEL7_IN_PIN, calcChannel7,CHANGE);
  attachInterrupt(CHANNEL8_IN_PIN, calcChannel8,CHANGE);

  // for loop back test only, lets set each channel to a known value
  servoChannel1.writeMicroseconds(1100);
  servoChannel2.writeMicroseconds(1200);
  servoChannel3.writeMicroseconds(1300);
  servoChannel4.writeMicroseconds(1400);
  servoChannel5.writeMicroseconds(1500);
  servoChannel6.writeMicroseconds(1600);
  servoChannel7.writeMicroseconds(1700);
  servoChannel8.writeMicroseconds(1800);
}

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 uint32_t unChannel1In;
  static uint32_t unChannel2In;
  static uint32_t unChannel3In;
  static uint32_t unChannel4In;
  static uint32_t unChannel5In;
  static uint32_t unChannel6In;
  static uint32_t unChannel7In;
  static uint32_t unChannel8In;
 
  // local copy of update flags
  static uint32_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 & CHANNEL1_FLAG)
    {
      unChannel1In = unChannel1InShared;
    }
  
    if(bUpdateFlags & CHANNEL2_FLAG)
    {
      unChannel2In = unChannel2InShared;
    }
  
    if(bUpdateFlags & CHANNEL3_FLAG)
    {
      unChannel3In = unChannel3InShared;
    }
   
    if(bUpdateFlags & CHANNEL4_FLAG)
    {
      unChannel4In = unChannel4InShared;
    }
  
    if(bUpdateFlags & CHANNEL5_FLAG)
    {
      unChannel5In = unChannel5InShared;
    }
  
    if(bUpdateFlags & CHANNEL6_FLAG)
    {
      unChannel6In = unChannel6InShared;
    }
   
    if(bUpdateFlags & CHANNEL7_FLAG)
    {
      unChannel7In = unChannel7InShared;
    }
  
    if(bUpdateFlags & CHANNEL8_FLAG)
    {
      unChannel8In = unChannel8InShared;
    }
    // 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 unChannel1, unChannel2, unChannel3, unChannel4, unChannel5, unChannel6, unChannel7, unChannel8
  // variables unChannel1InShared, unChannel2InShared, etc are always owned by the
  // the interrupt routines and should not be used in loop
 
  if(bUpdateFlags & CHANNEL1_FLAG)
  {
      // remove the // from the line below to implement pass through updates to the servo on this channel -
      //servoChannel1.writeMicroseconds(unChannel1In);
      Serial.println();
      Serial.print(unChannel1In);
      Serial.print(",");
  }

  if(bUpdateFlags & CHANNEL2_FLAG)
  {
      // remove the // from the line below to implement pass through updates to the servo on this channel -
      //servoChannel2.writeMicroseconds(unChannel2In);
      Serial.print(unChannel2In);
      Serial.print(",");
  }

  if(bUpdateFlags & CHANNEL3_FLAG)
  {
      // remove the // from the line below to implement pass through updates to the servo on this channel -
      //servoChannel3.writeMicroseconds(unChannel3In);
      Serial.print(unChannel3In);
      Serial.print(",");
  }

  if(bUpdateFlags & CHANNEL4_FLAG)
  {
    // remove the // from the line below to implement pass through updates to the servo on this channel -
    // servoChannel4.writeMicroseconds(unChannel4In);
    Serial.print(unChannel4In);
    Serial.print(",");
  }
 
  if(bUpdateFlags & CHANNEL5_FLAG)
  {
    // remove the // from the line below to implement pass through updates to the servo on this channel -
    // servoChannel5.writeMicroseconds(unChannel5In);
    Serial.print(unChannel5In);
    Serial.print(",");
  }
 
  if(bUpdateFlags & CHANNEL6_FLAG)
  {
    // remove the // from the line below to implement pass through updates to the servo on this channel -
    // servoChannel6.writeMicroseconds(unChannel6In);
    Serial.print(unChannel6In);
  }
 
  if(bUpdateFlags & CHANNEL7_FLAG)
  {
    // remove the // from the line below to implement pass through updates to the servo on this channel -
    // servoChannel7.writeMicroseconds(unChannel7In);
    Serial.print(unChannel7In);
    Serial.print(",");
  }
 
  if(bUpdateFlags & CHANNEL8_FLAG)
  {
    // remove the // from the line below to implement pass through updates to the servo on this channel -
    // servoChannel8.writeMicroseconds(unChannel8In);
    Serial.print(unChannel8In);
  }
 
  bUpdateFlags = 0;
}

void calcChannel1()
{
  static uint32_t ulStart;
 
  if(digitalRead(CHANNEL1_IN_PIN))
  {
    ulStart = micros();
  }
  else
  {
    unChannel1InShared = (uint32_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL1_FLAG;
  }
}

void calcChannel2()
{
  static uint32_t ulStart;
 
  if(digitalRead(CHANNEL2_IN_PIN))
  {
    ulStart = micros();
  }
  else
  {
    unChannel2InShared = (uint32_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL2_FLAG;
  }
}

void calcChannel3()
{
  static uint32_t ulStart;
 
  if(digitalRead(CHANNEL3_IN_PIN))
  {
    ulStart = micros();
  }
  else
  {
    unChannel3InShared = (uint32_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL3_FLAG;
  }
}

void calcChannel4()
{
  static uint32_t ulStart;
 
  if(digitalRead(CHANNEL4_IN_PIN))
  {
    ulStart = micros();
  }
  else
  {
    unChannel4InShared = (uint32_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL4_FLAG;
  }
}

void calcChannel5()
{
  static uint32_t ulStart;
 
  if(digitalRead(CHANNEL5_IN_PIN))
  {
    ulStart = micros();
  }
  else
  {
    unChannel5InShared = (uint32_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL5_FLAG;
  }
}

void calcChannel6()
{
  static uint32_t ulStart;
 
  if(digitalRead(CHANNEL6_IN_PIN))
  {
    ulStart = micros();
  }
  else
  {
    unChannel6InShared = (uint32_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL6_FLAG;
  }
}

void calcChannel7()
{
  static uint32_t ulStart;
 
  if(digitalRead(CHANNEL7_IN_PIN))
  {
    ulStart = micros();
  }
  else
  {
    unChannel7InShared = (uint32_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL7_FLAG;
  }
}

void calcChannel8()
{
  static uint32_t ulStart;
 
  if(digitalRead(CHANNEL8_IN_PIN))
  {
    ulStart = micros();
  }
  else
  {
    unChannel8InShared = (uint32_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL8_FLAG;
  }
}

Quick And Dirty Synth For Arduino Due

The first RCArduino project for the Arduino Due is the Quick And Dirty Synth. The synth is a simple showcase for audio output through the DAC running at the Audio CD sample rate of 44.1Khz.



RCArduino Quick And Dirty Synth by RCArduino is licensed under a
Creative Commons Attribution 3.0 Unported License.
Based on a work at rcarduino.blogspot.com.


The showcase is based on the simplest synth engine I could create - 3 counters counting up at a rate controlled by three analog inputs.

It might sound simple but its a surprisingly rich sounding synth engine, here is how it works - 

Two of the counters generate ramp waveforms - think about it, they are counting up from 0 to 4095, when they overflow, they go back to 0 and start the count again.


Example Ramp Output -  




Example Ramp At A Higher Frequency -

These ramp waveforms are summed together at the output to generate a more complex waveform - two ramp waves of independent frequency superimposed on each other.

Example - Two triangle at frequency F and 3F mixed together to create a new output waveform.

The third ramp waveform is used to control the pitch. It is not mixed with the output waveforms instead it achieves pitch control by resetting the first two waveforms.


Output waveform reset at frequency determined by third counter - notice that the counter is not directly present in the output but controls the repetition/synchronization of the output which in turn creates the pitch. 

To hear the technique in action connect three potentiometers to your Arduino Due on analog inputs 0,1,2 and an audio amplifier to DAC0.

All of the Audio projects on RCArduino use the following simple amplifier circuit -
http://rcarduino.blogspot.com/2012/08/adding-audio-to-arduino-projects.html

To learn more about the synthesis technique used in the quick and dirty synthesizer see the following link -

http://rcarduino.blogspot.com/2012/08/adding-audio-to-arduino-projects.html

The code 

Caution : The SAM3X8E microcontroller at the heart of the Arduino Due is less able to sink and source current than the AVR family of chips used in the 8-Bit Arduinos. I would suggest using a series resistor of around 500 Ohms when connecting the Arduino Due DAC to an external device. See this thread on the Arduino forum for more information - http://arduino.cc/forum/index.php/topic,139733.0.html
 

// RCArduino Quick And Dirty Synth for Arduino Due// RCArduino Quick And Dirty Synth by RCArduino is licensed under a Creative Commons Attribution 3.0 Unported License.
// Based on a work at rcarduino.blogspot.com.

// For helpful background information on Arduino Due Timer Configuration, refer to the following link
// thanks to Sebastian Vik
// http://arduino.cc/forum/index.php?action=post;topic=130423.15;num_replies=20

// The following folders within the arduino install provide access to source code and documentation
// its very low level, the documentation is next to useless, but it might help someone
// C:\arduino-1.5.1r2\hardware\arduino\sam\system\libsam\source
// C:/arduino-1.5.1r2/hardware/arduino/sam/system/CMSIS/Device/ATMEL/sam3xa/html/tc1.html
// C:/arduino-1.5.1r2/hardware/arduino/sam/system/CMSIS/Device/ATMEL/sam3xa/html/SAM3XA.html
// C:\arduino-1.5.1r2\hardware\arduino\sam\system\CMSIS\CMSIS\Documentation

// These are the clock frequencies available to the timers /2,/8,/32,/128
// 84Mhz/2 = 42.000 MHz
// 84Mhz/8 = 10.500 MHz
// 84Mhz/32 = 2.625 MHz
// 84Mhz/128 = 656.250 KHz
//
// 44.1Khz = CD Sample Rate
// Lets aim for as close to the CD Sample Rate as we can get -
//
// 42Mhz/44.1Khz = 952.38
// 10.5Mhz/44.1Khz = 238.09 // best fit divide by 8 = TIMER_CLOCK2 and 238 ticks per sample
// 2.625Hmz/44.1Khz = 59.5
// 656Khz/44.1Khz = 14.88

// 84Mhz/44.1Khz = 1904 instructions per tick

// These variables represent our synth engine, its similar to a vastly simplified Auduino and has a similar sound.
// Phase Accumulator controls the main pitch, grain1 and grain two phase accumulator control the pitch for the two grains
// The grainPhaseAccumulators are essentially simple counters, when you count up and overflow back to 0, you generate a ramp waveform
// we generate two and mix them together.
uint32_t ulPhaseAccumulator = 0; // 32 bit phase accumulator, if we shift >> 20 bits we get a 12 bit value for our output ADC
volatile uint32_t ulPhaseIncrement = 0;   // 32 bit phase increment, see below
uint32_t ulGrain1PhaseAccumulator = 0; // 32 bit phase accumulator, if we shift >> 20 bits we get a 12 bit value for our output ADC
volatile uint32_t ulGrain1PhaseIncrement = 0;   // 32 bit phase increment, see below
uint32_t ulGrain2PhaseAccumulator = 0; // 32 bit phase accumulator, if we shift >> 20 bits we get a 12 bit value for our output ADC
volatile uint32_t ulGrain2PhaseIncrement = 0;   // 32 bit phase increment, see below

// full waveform = 0 to 4294967296
// Phase Increment for 1 Hz =(4294967296/44100) = 1Hz
// Phase Increment for frequency F = (4294967296/44100)*F
#define SAMPLE_RATE 44100.0
#define TICKS_PER_CYCLE (4294967296.0/SAMPLE_RATE)

// Create a table to hold the phase increments we need to generate midi note frequencies at our 44.1Khz sample rate
#define MIDI_NOTES 128
uint32_t nMidiPhaseIncrement[MIDI_NOTES];

void createNoteTable(float fSampleRate)
{
  for(uint32_t unMidiNote = 0;unMidiNote < MIDI_NOTES;unMidiNote++)
  {
    // Correct calculation for frequency
    Serial.print(unMidiNote);
    Serial.print(" ");
    float fFrequency = ((pow(2.0,(unMidiNote-69.0)/12.0)) * 440.0);
    Serial.print(fFrequency);
    Serial.print(" ");
    nMidiPhaseIncrement[unMidiNote] = fFrequency*TICKS_PER_CYCLE;
    Serial.println(nMidiPhaseIncrement[unMidiNote]);
  }
}

void setup()
{
  Serial.begin(9600);

  createNoteTable(SAMPLE_RATE);
 
  /* turn on the timer clock in the power management controller */
  pmc_set_writeprotect(false);
  pmc_enable_periph_clk(ID_TC4);

  /* we want wavesel 01 with RC */
  TC_Configure(/* clock */TC1,/* channel */1, TC_CMR_WAVE | TC_CMR_WAVSEL_UP_RC | TC_CMR_TCCLKS_TIMER_CLOCK2);
  TC_SetRC(TC1, 1, 238); // sets <> 44.1 Khz interrupt rate
  TC_Start(TC1, 1);
 
  // enable timer interrupts on the timer
  TC1->TC_CHANNEL[1].TC_IER=TC_IER_CPCS;
  TC1->TC_CHANNEL[1].TC_IDR=~TC_IER_CPCS;
 
  /* Enable the interrupt in the nested vector interrupt controller */
  /* TC4_IRQn where 4 is the timer number * timer channels (3) + the channel number (=(1*3)+1) for timer1 channel1 */
  NVIC_EnableIRQ(TC4_IRQn);

  // this is a cheat - enable the DAC
  analogWrite(DAC0,0);
}

void loop()
{
  // read analog input 0 drop the range from 0-1024 to 0-127 with a right shift 3 places,
  // then look up the phaseIncrement required to generate the note in our nMidiPhaseIncrement table
  uint32_t ulInput = analogRead(0);
  ulPhaseIncrement = nMidiPhaseIncrement[ulInput>>3];
 
  // set the phase increment for grains 1 and 2, we do not want a precise frequency for these,
  // they set the character of the note rather than pitch
  ulGrain1PhaseIncrement = analogRead(1)<<18;
  ulGrain2PhaseIncrement = analogRead(2)<<18;
}

void TC4_Handler()
{
  // We need to get the status to clear it and allow the interrupt to fire again
  TC_GetStatus(TC1, 1);
 
  ulPhaseAccumulator += ulPhaseIncrement;   // 32 bit phase increment, see below
  // if the phase accumulator over flows - we have been through one cycle at the current pitch,
  // now we need to reset the grains ready for our next cycle
  if(ulPhaseAccumulator < ulPhaseIncrement)
  {
   ulGrain1PhaseAccumulator = 0;
   ulGrain2PhaseAccumulator = 0;
  }
  else
  {
   // increment the grains
   ulGrain1PhaseAccumulator += ulGrain1PhaseIncrement;
   ulGrain2PhaseAccumulator += ulGrain2PhaseIncrement;
  }
 
  // mix the grains by adding them together - to the result of adding these two 32bit values into the 12 bit ADC Output
  // we shift both values right 21 places to sum two 11 bit values giving a 12 bit result.
  uint32_t ulOutput = (ulGrain1PhaseAccumulator>>21)+(ulGrain2PhaseAccumulator>>21);
 
  // we cheated and user analogWrite to enable the dac, but here we want to be fast so
  // write directly 
  dacc_write_conversion_data(DACC_INTERFACE, ulOutput);
}