#define port1 5 
#define port2 6
#define SW1 4
#define SW2 7

int val; // variable 
// a '1' or HIGH are both understood to both be a binary 1.
// a HIGH on a port pin is 5 volts.
// a '0' or LOW are both understood to be a binary 0.
// a LOW on a port pin is 0 volts.

void setup()  {
   pinMode(port1, OUTPUT);  // DL1 TA8050 H bridge
   pinMode(port2, OUTPUT);  // DL2 TA8050 H bridge
   pinMode(SW1, INPUT);
   pinMode(SW2, INPUT);

   digitalWrite(SW1, 1); // pull up on
   digitalWrite(SW2, 1); // pull up on
   // turn off 'H' bridge:
   analogWrite(port1, 0); // 0 volts out or LOW
   analogWrite(port2, 0); // 0 volts out or LOW
   
   } // end setup

void loop() {  // main loop
 
   //  If neither SW1 or SW2 are pushed a digitalRead(pin) will return a HIGH because of the pull ups.
   //  A return of LOW means the switch was pressed.  
   //  A zero is written to both PWMs on port1 and port2 will output a LOW.
   //  We need to get the value from a speed control (variable resistor) connected 
   // analog input 0. This ten-bit value from 0-1023 must be divided by four before
   // being written to a PWM pin which is 8 bits.
   val = analogRead(0) / 4 ;
   
   //If we press SW1:
   if (digitalRead(SW1) == 0) {
     analogWrite(port1, val); // write val to PWM port1.
     analogWrite(port2, 0);
   }
   
   // If we press SW2:
   if (digitalRead(SW2) == 0) {
     analogWrite(port1, 0); // write val to PWM port2.
     analogWrite(port2, val);
   }
   
   // while either switch is held down one can adjust the speed real time.
   
   // if both switches are pushed at the same time the motor will stop
   if ((digitalRead(SW1) == 0) && (digitalRead(SW2) == 0)) {
     analogWrite(port1, 0);
     analogWrite(port2, 0);
     delay(500); // delay half second for key release
   } 
       
} // end loop