Red Box Robot Hookup Guide

Contributors: Nick Poole
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Avoiding Obstacles

Before we upload fresh code to take advantage of our robot's ultrasonic sensor, we'll need to wire the sensor to the RedStick. This sensor only requires four wires to work, and I've highlighted them in the diagram below.

wiring diagram

Having a hard time seeing the circuit? Click on the wiring diagram for a closer look.

Once you've added these wires, it's just a matter of uploading the example code below:

#include <SparkFun_TB6612.h>

// these constants are used to allow you to make your motor configuration 
// line up with function names like forward.  Value can be 1 or -1
const int offsetA = -1;
const int offsetB = -1;

// Pins for all inputs, keep in mind the PWM defines must be on PWM pins
// the default pins listed are the ones used on the Redbot (ROB-12097) with
// the exception of STBY which the Redbot controls with a physical switch
#define AIN1 2
#define BIN1 7
#define AIN2 4
#define BIN2 5
#define PWMA 10
#define PWMB 6
#define STBY 9

// Initializing motors.  The library will allow you to initialize as many
// motors as you have memory for.  If you are using functions like forward
// that take 2 motors as arguements you can either write new functions or
// call the function more than once.
Motor motor1 = Motor(AIN1, AIN2, PWMA, offsetA, STBY);
Motor motor2 = Motor(BIN1, BIN2, PWMB, offsetB, STBY);

// Pins
const int TRIG_PIN = 11;
const int ECHO_PIN = 12;

// Anything over 400 cm (23200 us pulse) is "out of range"
const unsigned int MAX_DIST = 23200;

void setup() {

  // Setup all of our pins
  pinMode(TRIG_PIN, OUTPUT);
  digitalWrite(TRIG_PIN, LOW);
  pinMode(2, OUTPUT); digitalWrite(2, LOW);
  pinMode(4, OUTPUT); digitalWrite(4, LOW);
  pinMode(5, OUTPUT); digitalWrite(5, LOW);
  pinMode(7, OUTPUT); digitalWrite(7, LOW);
  pinMode(3, OUTPUT); 
  pinMode(6, OUTPUT); 
  pinMode(A4, OUTPUT);
  digitalWrite(A4, HIGH);


void loop() {

  // Start moving forward
  forward(motor1, motor2, 200);

  unsigned long t1;
  unsigned long t2;
  unsigned long pulse_width;
  float cm;

  // Hold the trigger pin high for at least 10 us
  digitalWrite(TRIG_PIN, HIGH);
  digitalWrite(TRIG_PIN, LOW);

  // Wait for pulse on echo pin
  while ( digitalRead(ECHO_PIN) == 0 );

  // Measure how long the echo pin was held high (pulse width)
  // Note: the micros() counter will overflow after ~70 min
  t1 = micros();
  while ( digitalRead(ECHO_PIN) == 1);
  t2 = micros();
  pulse_width = t2 - t1;

  // Calculate distance in centimeters.
  cm = pulse_width / 58.0;

  // If an obstacle is detected fewer than 20 centimeters away,
  // run the motors backwards and then coin flip to decide which
  // way to turn before continuing on.
  if(cm<20){back(motor1, motor2, 250); delay(1000);
  if(flip()){left(motor1, motor2, 250);}else{right(motor1, motor2, 250);}

  // Wait at least 60ms before next measurement

// Coinflip function that randomly returns a 1 or 0
bool flip(){

  static uint32_t buf = 0;
  static uint8_t idx = 0;
  if (idx)
    buf >>= 1;
    buf = random();  // refill
    idx = 30;
  return buf & 0x01;


If everything is working correctly, your robot should be dodging obstacles. More specifically, if an object comes within 20 centimeters of the front of the robot, the robot will reverse direction and turn randomly before continuing on its way. This is a nice self-preservation instinct for a robot to have. However, if science fiction movies have taught me anything, a small robot needs a cute voice to survive.