Experimenting with smart LEDs on an RC Car…

These are Adafruit Pixie Chainable Smart LEDs and an Arduino Uno.  On the car I replaced both channel’s servo cables with Y-harnesses.   Plugging one end of each harness back in to the servo/ESC, the other end is used to connect to Arduino PWM input pins.  Reading those values and using that information to  control the LEDs.  Adafruit Pixie LEDs are chained together but individually assignable to any color by the program.  This allows for making turn signals when turning the vehicle and also being able to do other things with the lights when the car is throttled or neutral.  I only have two LEDs in this example, but you could string more than that together.

Source code for the video demo:

/*
  This sketch is for two Smart LEDs on an RC car as programmable headlights.
     - Neutral position = "demon eye" red transition
     - Left turn        = left turn signal
     - Right turn       = right turn signal
     - Throttle         = blue, variable brightness
     - Full throttle    = white flashing

     Author:  John Reed  johnnycarlos@gmail.com
*/

#include "SoftwareSerial.h"
#include "Adafruit_Pixie.h"

#define NUMPIXELS 2 // Number of Pixies in the strip
#define PIXIEPIN  6 // Pin number for SoftwareSerial output
#define UP        1
#define DOWN      2
#define INCREMENT 2
#define OFF       0
#define LEFT_LED  0
#define RIGHT_LED 1
#define BRIGHTNESS     200
#define MAX_BRIGHTNESS 255
#define FLASH_DELAY    100

byte SERVOPIN    = 3;
byte THROTTLEPIN = 5;
int servoPWM;
int throttlePWM;


#define MAX_RED 254
#define MIN_RED 20
int currentRed = 0;

// Servo signal PWM values
int leftThreshold     = 1400;
int rightThreshold    = 1600;
int throttleThreshold = 1550;
int fadeDirection     = UP;

SoftwareSerial pixieSerial(-1, PIXIEPIN);
Adafruit_Pixie strip = Adafruit_Pixie(NUMPIXELS, &pixieSerial);

void setup() {

  pinMode(SERVOPIN,    INPUT);
  pinMode(THROTTLEPIN, INPUT);

  Serial.begin(9600);

  pixieSerial.begin(115200); // Pixie REQUIRES this baud rate

  // brightness is 0 to 255
  strip.setBrightness(BRIGHTNESS);

}

void loop() {

  // Measure servo values and then map them to the lights
  servoPWM    = pulseIn(SERVOPIN, HIGH);
  throttlePWM = pulseIn(THROTTLEPIN, HIGH);

  if(throttlePWM > throttleThreshold){
      whiteDoubleFlash();
  }
  
  if( servoPWM < leftThreshold ){ turnSignal(LEFT_LED); } else if( servoPWM > rightThreshold ){
      turnSignal(RIGHT_LED);
  }
  else{
      demonEyes();
  }
  
}

/*
 * Slow fading red.
 * 
 * Since this is a slow light sequence, I needed to make it interruptable
 * so there isn't a delay changing to another light sequence.  I did this by maintaining the
 * current light value.  Once per loop I inc/dec the current light value(depending on whater it's fading in or out) 
 * and display it.  This gives the loop a chance to decide to do something else.
 * The fade rate is entirely dependent on the speed of the main loop.  If the loop is very busy, for example, demonEyes  
 * wont refresh as often.  Thus, the INCREMENT value can be changed to compensate.
 */
void demonEyes(){
  
    if( fadeDirection == UP ){

        if( currentRed < MAX_RED ){ currentRed += INCREMENT; strip.setBrightness(currentRed); strip.setPixelColor(LEFT_LED, 255, 0, 0); strip.setPixelColor(RIGHT_LED, 255, 0, 0); strip.show(); } else{ fadeDirection = DOWN; } } else { if( currentRed > MIN_RED ){
            currentRed -= INCREMENT;
            strip.setBrightness(currentRed);
            strip.setPixelColor(LEFT_LED, 255, 0, 0);
            strip.setPixelColor(RIGHT_LED, 255, 0, 0);
            strip.show();

        }
        else{
          fadeDirection = UP;
        }
    }

}

/*
 * Flashes amber once.  Takes a NUMPIXELS(the LED number in the chain) that will flash.
 */
void turnSignal(int ledNum){

    int otherLed;
    if( ledNum == 0 ){
        otherLed = 1;
    }
    else{
        otherLed = 0;
    }

    strip.setBrightness(BRIGHTNESS);
    strip.setPixelColor(ledNum, 255, 125, 0);
    strip.setPixelColor(otherLed, 0, 0, 0);
    strip.show();
    delay(500);
    
    strip.setBrightness(OFF);
    strip.show();
    delay(300);
  
}

/*
 * Bright white double flash.
 */
void whiteDoubleFlash(){

    // Loop twice.  Two flashes
    for( int i = 0; i < 2; i++ ){
        strip.setBrightness(MAX_BRIGHTNESS);
        strip.setPixelColor(LEFT_LED, 255, 255, 255);
        strip.setPixelColor(RIGHT_LED, 255, 255, 255);
        strip.show();
        delay(FLASH_DELAY);

        strip.setBrightness(OFF);
        strip.show();
        delay(FLASH_DELAY);
    }
    
}

These are my notes on how to use a remote control’s switches to control extra features of a robot.  In my case, I have an autonomous rover and would like to build a switch to press on the remote control to stop the rover and take manual control over it.

I used a Spektrum DX4C transceiver.

First, I configured the Spektrum  DX4C profile model in memory so that Channel 3 will be used as a switch.  To do this:

1. Press the scroll wheel and select your Model to configure
2. Next, scroll down to Switch
3. For menu selection “A:”, choose Aux1 SP2

Next I connected a pin wire from the receiver.  On my Spectrum SR3100, this was labelled Aux.   I connected the wire to an Arduino PWM capable pin(5).  Make sure the receiver has power.  You can get it from the Arduino board’s 5v and ground pins.

The following sketch allowed me to read the values of the switch:

/*
 * To read the values go to Tools | Serial Monitor
 */

byte pin = 5;
 
int value;
 
void setup() {
  pinMode(pin, INPUT);
  Serial.begin(9600);
}
 
void loop() {
  value = pulseIn(pin, HIGH);
  Serial.println(value);
  delay(500);
}

Pressing the switch gave me approximately the following PWM values:

Switch On:  1900

Switch Off: 1100

Radio Off:  1500

In conclusion, these values would be used in an Arduino sketch to control a robot’s behavior.  Use code logic to determine if the switch is on/off and use that to display a light, play a sound, or any behavior altering characteristic you can imagine.