Problem reading RC Channels - The RCArduino Loop Back Test

Many people experience problems adding additional channels to the RCArduino test sketches or porting them to new devices, its usually down to mistakes in the way the additional channels are coded

This post presents an example of managing 8 input/output channels, its a very simple sketch which outputs 8 RC Channels and reads them right back in again.

The sketch can be used in three steps -

1) Initially the sketch outputs fixed values for the servos and reads them back in as a loop back test.

2) Once you are comfortable with the code, you can replace one or more of the loop back connections to start reading RC Channels. 

3) Once you are confident that the sketch is reading your channels correctly you can connect your servos and ESCs to the outputs and your done, 8 channels in, 8 channels out in three easy steps.


Step 1 - Loop back testing
To use the loop back test in step 1, connect pins 2 to 9 (the channel inputs) to pins 10 to 13 and A0 to A3 (the channel outputs).

Each channel is set to a fixed output from 1100 to 1800, if the code works on your board, your should see these values being output in the serial monitor.

Step 2 - RC Channel reading

Once you have this up and running, you can start swapping the connections to an RC receiver one by one. You should now see the channel values for the receiver channels updating in your serial monitor. If the values are within a range of around 1000 to 2000, your ready to move to step 3.

Step 3 - Full Control
To start outputting the values that you have read in, remove the comments from the servoName.writeMicroseconds functions to have full control of upto 8 servos/escs using 8 RC Receiver channels.

If it does not work, let me know which board you have, the code is easily adapted to work on any of the 8-bit Arduino boards. If you have a 32 bit Arduino Due, there is a dedicated post here -

http://rcarduino.blogspot.ae/2013/04/reading-rc-channels-with-arduino-due.html

For more performance and smoother output on the 8-bit Arduinos an RCArduinoFastLib versions will be added in separate in the coming days.

// RCArduino MultiChannel Loop back and servo ESC control for upto 8 RC channels
//
// 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>

#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 A0
#define CHANNEL6_OUT_PIN A1
#define CHANNEL7_OUT_PIN A2
#define CHANNEL8_OUT_PIN A3

// 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 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 unChannel1InShared;
volatile uint16_t unChannel2InShared;
volatile uint16_t unChannel3InShared;
volatile uint16_t unChannel4InShared;
volatile uint16_t unChannel5InShared;
volatile uint16_t unChannel6InShared;
volatile uint16_t unChannel7InShared;
volatile uint16_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);

  // using the PinChangeInt library, attach the interrupts
  // used to read the channels
  PCintPort::attachInterrupt(CHANNEL1_IN_PIN, calcChannel1,CHANGE);
  PCintPort::attachInterrupt(CHANNEL2_IN_PIN, calcChannel2,CHANGE);
  PCintPort::attachInterrupt(CHANNEL3_IN_PIN, calcChannel3,CHANGE);
  PCintPort::attachInterrupt(CHANNEL4_IN_PIN, calcChannel4,CHANGE);
  PCintPort::attachInterrupt(CHANNEL5_IN_PIN, calcChannel5,CHANGE);
  PCintPort::attachInterrupt(CHANNEL6_IN_PIN, calcChannel6,CHANGE);
  PCintPort::attachInterrupt(CHANNEL7_IN_PIN, calcChannel7,CHANGE);
  PCintPort::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 uint16_t unChannel1In;
  static uint16_t unChannel2In;
  static uint16_t unChannel3In;
  static uint16_t unChannel4In;
  static uint16_t unChannel5In;
  static uint16_t unChannel6In;
  static uint16_t unChannel7In;
  static uint16_t unChannel8In;

  uint8_t bUpdateFlags = 0;
  // check shared update flags to see if any channels have a new signal
  // for nicely formatted serial output use this
  if(bUpdateFlagsShared == 0xFF)
  // for more responsive projects update any channels whenever a new signal is available using this
  // 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 unAuxIn, unThrottleIn and unSteeringIn, the shared
  // variables unAuxInShared, unThrottleInShared, unSteeringInShared are always owned by
  // the interrupt routines and should not be used in loop
  if(bUpdateFlags & CHANNEL1_FLAG)
  {
      // when you are ready to add a servo or esc, remove the // from the following line to use the channel input to control it
      // servoChannel1.writeMicroseconds(unChannel1In);
      Serial.println("");
      Serial.print(bUpdateFlags);
      Serial.print(",");
      Serial.print(unChannel1In);
      Serial.print(",");
  }
 
  if(bUpdateFlags & CHANNEL2_FLAG)
  {
      // when you are ready to add a servo or esc, remove the // from the following line to use the channel input to control it
      // servoChannel2.writeMicroseconds(unChannel2In);
      Serial.print(unChannel2In);
      Serial.print(",");
  }
 
  if(bUpdateFlags & CHANNEL3_FLAG)
  {
      // when you are ready to add a servo or esc, remove the // from the following line to use the channel input to control it
      // servoChannel3.writeMicroseconds(unChannel3In);
      Serial.print(unChannel3In);
      Serial.print(",");
  }
 
  if(bUpdateFlags & CHANNEL4_FLAG)
  {
      // when you are ready to add a servo or esc, remove the // from the following line to use the channel input to control it
      // servoChannel4.writeMicroseconds(unChannel4In);
      Serial.print(unChannel4In);
      Serial.print(",");
  }
 
  if(bUpdateFlags & CHANNEL5_FLAG)
  {
      // when you are ready to add a servo or esc, remove the // from the following line to use the channel input to control it
      // servoChannel5.writeMicroseconds(unChannel5In);
      Serial.print(unChannel5In);
      Serial.print(",");
  }
 
  if(bUpdateFlags & CHANNEL6_FLAG)
  {
      // when you are ready to add a servo or esc, remove the // from the following line to use the channel input to control it
      // servoChannel6.writeMicroseconds(unChannel6In);
      Serial.print(unChannel6In);
      Serial.print(",");
  }
 
  if(bUpdateFlags & CHANNEL7_FLAG)
  {
      // when you are ready to add a servo or esc, remove the // from the following line to use the channel input to control it
      // servoChannel7.writeMicroseconds(unChannel7In);
      Serial.print(unChannel7In);
      Serial.print(",");
  }
 
  if(bUpdateFlags & CHANNEL8_FLAG)
  {
      // when you are ready to add a servo or esc, remove the // from the following line to use the channel input to control it
      // servoChannel8.writeMicroseconds(unChannel8In);
      Serial.print(unChannel8In);
      Serial.print(",");
  }
}


void calcChannel1()
{
  static uint32_t ulStart;
 
  if(PCintPort::pinState) // this is equivalent to digitalRead(CHANNEL1_IN_PIN) but about 10 times faster
  {
    ulStart = micros();
  }
  else
  {
    unChannel1InShared = (uint16_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL1_FLAG;
  }
}

void calcChannel2()
{
  static uint32_t ulStart;
 
  if(PCintPort::pinState)
  {
    ulStart = micros();
  }
  else
  {
    unChannel2InShared = (uint16_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL2_FLAG;
  }
}

void calcChannel3()
{
  static uint32_t ulStart;
 
  if(PCintPort::pinState)
  {
    ulStart = micros();
  }
  else
  {
    unChannel3InShared = (uint16_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL3_FLAG;
  }
}

void calcChannel4()
{
  static uint32_t ulStart;
 
  if(PCintPort::pinState)
  {
    ulStart = micros();
  }
  else
  {
    unChannel4InShared = (uint16_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL4_FLAG;
  }
}

void calcChannel5()
{
  static uint32_t ulStart;
 
  if(PCintPort::pinState)
  {
    ulStart = micros();
  }
  else
  {
    unChannel5InShared = (uint16_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL5_FLAG;
  }
}

void calcChannel6()
{
  static uint32_t ulStart;
 
  if(PCintPort::pinState)
  {
    ulStart = micros();
  }
  else
  {
    unChannel6InShared = (uint16_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL6_FLAG;
  }
}

void calcChannel7()
{
  static uint32_t ulStart;
 
  if(PCintPort::pinState)
  {
    ulStart = micros();
  }
  else
  {
    unChannel7InShared = (uint16_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL7_FLAG;
  }
}

void calcChannel8()
{
  static uint32_t ulStart;
 
  if(PCintPort::pinState)
  {
    ulStart = micros();
  }
  else
  {
    unChannel8InShared = (uint16_t)(micros() - ulStart);
    bUpdateFlagsShared |= CHANNEL8_FLAG;
  }
}Duane B

Lap Timer Part 5 - Buzzer, External Audio and Some Builds

The latest version of the lap timer includes two new features -

1) External Audio - There is now an option to use a very simple amplifier circuit which is small enough to fit inside most project boxes. This will give you a lot more volume when you are using the system outdoors.

2) Countdown - With countdown switched on, the lap timer will beep to count down the last few seconds of the current lap time - it adds a little extra pressure - to beat the lap you have to beat the beeps.

For previous steps of the build along see the project index page -
http://rcarduino.blogspot.com/p/project-index.html

Before we get to the build, here are some user pictures of current builds, if you have pictures of your own build I am happy to share them.

ALLY - Transponder mounted in touring car chassis

Howie314 - Using an LCD Shield for a fast build
	This build by Arduino Forum User Howie314 uses a LCD Keypad Shield, it keeps the size down and means there is very little soldering required to build the project. Many LCD Shields are available and all work in a similar manner meaning that you can get a lap timer up and running quickly with almost no soldering required. If someone would design an LCD Shield with a rotary encoder as well as buttons we could have the perfect lap timer interface.
	Howie314 is one of the first using the most recent version of the code with the new options of external audio and countdown. Additional options that I am considering in the near future are 1) Window magnet transponders and 2) AIM Transponders. See the end of post for more details.
	Howie also did some work on the user interface as the LCD Shield uses a single analog pin to read multiple buttons. It makes sense to offer a version of the build along based on these readily available shields so I will be taking a look at Howies modifications with a plan to offer a single version of the project which can be run on standalone builds or LCD Shields - props to Howie.

ALLY's Build and Enclosure	Arduino forum user ALLY has used a standalone LCD and soldered his own buttons. This gives a bit more flexibility in the type of display and enclosures you can use, but also requires more work to build.
ALLY Transponder Mount	Here is a shot of ALLY's transponder mounted in his RC Touring car. Notice that the IR Emitter is mounted on a small post, this is a nice solution as the LED is well away from any areas that would impact in a crash. If you want to try something similar make sure to keep the wires to the LED short. I tried wires of about 15 cm which unfortunately acted as an antenna causing radio interference.
ALLY's Carbon	ALLY has used a large carbon fibre effect enclosure, there is lots of room to add indicator LEDs, or one of my favorite features - a small amplifier for optional external speakers.

Lap Timer Piezo Buzzer and External Audio
One of the most useful features of the lap timer is instant audio feedback, this is particularly important with RC Car racing and Kart racing where corners are fractions of a second apart and checking a display is not an option.

The feedback is deliberately simple but totally effective - one beep to confirm a lap and two beeps if its a new best lap.

To add the audio features we have two options

1) A Piezo Buzzer
2) An External Speaker

I have found it useful to have both options in my build, using the quieter peizo for testing near my home and the external audio to overcome the additional noise at the track, the latest code includes a menu to switch between these two output options.

Piezo With Transistor Driver
To get as much volume as possible from the buzzer we can drive it using the battery voltage rather than the regulated 5 volts from the Arduino. To switch the higher battery voltage from an Arduino pin we use a NPN transistor connected between the piezo (the load) and ground. This arrangement allows us to switch the higher voltages and currents through the Peizo and can also be applied to other loads such as high powered LEDs, relays and other components you may want to use in your future projects.



Components
1 * 2.2K Resistor
1 * P2N2222 Transistor
1 * Piezo Buzzer 

External Audio Through A Speaker
The Peizo option can be used without adding the external audio option, but if you want more volume in your build read on -

In order to power a speaker we need a few more components to drive the extra current, one easy to use option is the LM386 Audio Amp chip. This is used extensively throughout the RCArduino blog in a variety of audio projects, full details and videos of the chip in action cab be found here -

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

The LM386 Audio Amp can be build to a very compact form factor to fit your chosen enclosure -

Parts List
1 x LM386-N4
2 x 100uf Electrolytic Capacitors
1 x 0.1uf Capacitor
1 x 100Ohm Resistor
1 x 10K Potentiometer1 x Phono socket for speaker connection



Schematic - Note the audio output is from analog pin 5, for simplicity only the audio components are shown, as there

For the latest code, contact me Duane B though the Arduino forum.

Future Developments
Some common requests that I will be adding in the near future are -

1) Support for individual transponders - this will take some experimenting, but it should be possible to create a simple transponder scheme which will allow several lap timers to be used simultaneously with each car paired to a specific lap timer.

2) Support for magnetic transponders - I am told that many kart tracks use a magnetic strip under the track to activate transponders which are similar to magnetic window sensors, I hope to work with an Arduino forum user to add support for this option, it should be simple, but I have nowhere to test the system locally.

Inspired by Howie314's use of an off the shelf LCD Shield I will also add support for a build along based on this quick start option.

If you have a build you want to share, please submit some pictures,

Stay Tuned

Duane B