File content as of revision 0:10883d5ab141:

#include "mbed.h"
#include "motordriver.h"

Serial pc(USBTX, USBRX);
Serial device(p9, p10); //Connect JY-MCU bluetooth module to 9,10

Motor  right(p21, p22, p23, 1); // pwm, fwd, rev, has brake feature
Motor left(p26, p25, p24, 1);

DigitalIn Enc1(p19); //right motor
DigitalIn Enc2(p20); //left motor
int oldEnc1 = 0; //Was the encoder previously a 1 or zero?
int oldEnc2 = 0;

int ticksR = 0; //How many times has the Right wheel encoder changed state? 
int ticksL = 0; //Same for left wheel
int E; // the error  between the 2 wheel speeds
float speedL =0; //PWM speed setting for left wheel (scaled between 0 and 1)
float speedR=0; //Same for right wheel
Ticker Sampler; //Interrupt Routine to sample encoder ticks.
unsigned char Instr = 0;//What button was sent from app?
unsigned char sentSpeed = 0; //What is the speed slider set to?

void sampleEncoder(); //Function for sampling and adjusting speeds. 

int main()
{
    Sampler.attach(&sampleEncoder, .02); //Sampler uses sampleEncoder function every 20ms
    Enc1.mode(PullUp); // requires a pullup resistor so i just used embed's feature.
    Enc2.mode(PullUp);
    device.baud(57600); //Baud rate of JY-MCU (not Default!) 

    while(1) {
        if(device.readable()) { //If the bluetooth has sent data, get the instruction
            Instr = device.getc();
            wait(.05);//Wait for the next bluetooth value to be recieved.
            if(device.readable()) {//Now get the speed
                sentSpeed = device.getc();
                switch (Instr) {
                    case 0://Stop
                        left.speed(0);
                        right.speed(0);
                        break;
                    case 1://Forward

                        speedL = float(sentSpeed) / 100;;
                        speedR = speedL;
                        left.speed(speedL);
                        right.speed(speedR);
                        break;
                    case 2://Reverse (not currently implemented in app
                        speedL = -float(sentSpeed) / 100;;
                        speedR = speedL;
                        left.speed(speedL);
                        right.speed(speedR);
                        break;
                    case 3://Clockwise Turn
                        speedL = float(sentSpeed) / 100;
                        left.speed(speedL);
                        right.speed(-speedL);
                        break;
                    case 4://CCW Turn
                        speedL = float(sentSpeed) / 100;
                        left.speed(-speedL);
                        right.speed(speedL);
                        break;
                }//End Switch

            }//End Speed Read
        }//End Instruction Read
        if(Instr == 1 || Instr == 2) { // Only increment tick values if moving forward or reverse
            if(Enc1 != oldEnc1) { // Increment ticks every time the state has switched. 
                ticksR++;
                oldEnc1 = Enc1;

            }
            if(Enc2 != oldEnc2) {
                ticksL++;
                oldEnc2 = Enc2;
            }
        }

    }
}

//Sample encoders and find error on right wheel. Assume Left wheel is always correct speed.
void sampleEncoder()
{
    if((Instr == 1 || Instr == 2) && ticksL != 0) { //Make sure the robot is moving forward or reversed and that left wheel hasn't stopped. 

        E = ticksL - ticksR; //Find error
        speedR = speedR + float(E) / 255.0f; //Assign a scaled increment to the right wheel based on error
        if(Instr == 1) speedR = speedR + float(E) / 255.0f;
        //Reverse not implemented.  
        right.speed(speedR);
    }
    ticksR = 0; //Restart the counters
    ticksL = 0;
}