Week 4 - Servos and Photocells
So, this simple lab was incredibly useful to me. Even though we had spent several classes talking about the importance of resistors in the analog pipeline, I conveniently forgot where and how to implement them. I wired my breadboard just fine and made sure to get my hands on the proper code, it wasn’t until I dropped a resistor on the same bus as the analog in and connected it to ground did I realize exaclt why it was necessary. My understanding might be limited but I am going to attempt to explain why I think it worked. If I understand it correctly it’s because the electricity in the circuit needs a bumper of sorts from dissipating through the board. Or to put it another way the resistor linking it to ground creates a closed system so electricity moving through the photocell has another discreet channel to move through. I hope someone who understands this can either correct me or tell me why I’m wrong.
Anyway, once the wiring was good and I realized the value range coming off of the photocell was consistent within a certain range I just adjusted the code accordigly so the values were mapped properly. I think my next step will be to throw a potentiometer on there and see if I can control the motor with more precision.
Here’s my code:
int servoPin = 2; // Control pin for servo motor
int minPulse = 500; // Minimum servo position
int maxPulse = 2500; // Maximum servo position
int pulse = 0; // Amount to pulse the servo
long lastPulse = 0; // the time in milliseconds of the last pulse
int refreshTime = 20; // the time needed in between pulses
int analogValue = 0; // the value returned from the analog sensor
int analogPin = 0; // the analog pin that the sensor’s on
void setup() {
pinMode(servoPin, OUTPUT); // Set servo pin as an output pin
pulse = minPulse; // Set the motor position value to the minimum
Serial.begin(9600);
}
void loop() {
analogValue = analogRead(analogPin); // read the analog input
pulse = map(analogValue,50,500,minPulse,maxPulse); // convert the analog value
// to a range between minPulse
// and maxPulse.
// pulse the servo again if rhe refresh time (20 ms) have passed:
if (millis() - lastPulse >= refreshTime) {
digitalWrite(servoPin, HIGH); // Turn the motor on
delayMicroseconds(pulse); // Length of the pulse sets the motor position
digitalWrite(servoPin, LOW); // Turn the motor off
lastPulse = millis(); // save the time of the last pulse
}
}
