Using map for DC motor instead of servo

Question

I am trying to use map command which is used to power servo 180 degrees as the potentiometer moves...

in fact what i want to do is just when i adjust my potentiometer to zero; stop the dc motor then after turn the pot to 512 analog value turn the motor to the left (digitalWrite(I1, HIGH); digitalWrite(I2, LOW);)and then stop when it reach 512 then when adjust the pot back to zero turn the dc motor to the right (digitalWrite(I1, HIGH); digitalWrite(I2, LOW);) but the think is what i am trying to do is exactly what we can do with the servo motor in the knob http://www.arduino.cc/en/Tutorial/Knob

I'm using a normal DC motor and l293D IC but I want to control the DC as knob method like the 200 degrees.

Code

#define E1 11 // Enable Pin for motor 
#define I1 10 // Control pin a for motor 
#define I2 9 // Control pin b for motor 
const int analogPin = A0; 
int analogValue ; 
void setup() {
 pinMode(E1, OUTPUT);
 pinMode(I1, OUTPUT);
 pinMode(I2, OUTPUT);
}
void loop() {
 int analogValue = analogRead(analogPin);
 if(analogValue > 0 && analogValue < 512) {
 analogWrite(E1, 255); 
 digitalWrite(I1, HIGH);
 digitalWrite(I2, LOW);
 delay(100); 
} else 
 analogWrite(E1, 255); 
 digitalWrite(I1, LOW);
 digitalWrite(I2, HIGH);
 }

• Dmitry Grigoryev: Any chance to have a circuit diagram?
• Nedd: The map function doesn't seem to be included in your second section of code. Did you want to adjust the 255 value to a new value relative to the "analogValue"?
• Chris Stratton: "and then stop when it reach 512" is meaningless for a DC motor unless you have a position feedback device connected to it. Hobby type servos include an internal potentiometer for feedback. If you are building a position control with an ordinary DC motor, you will have to mechanical link something such as an encoder or potentiometer to its shaft and implement a position control loop.

Answer 1

It looks like you want to use the "analogValue" to control the direction and speed of your DC motor. If this is correct consider using this:

 //This method assumes: The center position of the pot is the motor's 0 speed point, 
 //(because this is an ideal speed to actually reverse the motor's direction).
 //A PWM control range of 0-255, and the ADC input range of 0-1023. 
 //First create a relative speed value from "analogValue", 
 //with the pot mid point at 0 speed, and pot high/low points being full speed. 
 int motorSpeed = 0; 
 if (analogValue < 512 ) 
 { 
 motorSpeed = map(analogValue, 0, 511, 255, 0); 
 } //Note that mapped range is reversed to give 0 speed at mid point. 
 else 
 { 
 motorSpeed = map(analogValue, 512, 1023, 0, 255); 
 }
 //then replace each analogWrite(E1, 255) with: 
 analogWrite(E1, speedValue); 
 //you should also change " if (analogValue > 2 && analogValue < 500) { " to: 
 if (analogValue < 512) { 

• mohammad: thanks for this kind answer, in fact what i want to do is just when i adjust my potentiometer to zero; stop the dc motor then after turn the pot to 512 analog value turn the motor to the left (digitalWrite(I1, HIGH); digitalWrite(I2, LOW);)and then stop when it reach 512 then when adjust the pot back to zero turn the dc motor to the right (digitalWrite(I1, HIGH); digitalWrite(I2, LOW);) but the think is what i am trying to do is exactly what we can do with the servo motor in the knob arduino.cc/en/Tutorial/Knob
• mohammad: youtube.com/watch?v=3mw6H3461Y0
• mohammad: IT IS AN EXAMPLE