Lachlan's avatar@lachlanjc/edu
All Physical Computing

Week 3 – Servo Motor

I successfully wired up a Force-Sensing Resistor to my Servo motor:

Code from this video:

#include "Servo.h"


Servo servoMotor;
long lastMoveTime = 0;  
 
void setup() {
  Serial.begin(9600);
  servoMotor.attach(9);
} 
 
void loop() {
  int analogValue = analogRead(A0);
  int servoAngle = map(analogValue, 0, 1023, 0, 179);


  if (millis() - lastMoveTime > 20) {
    servoMotor.write(servoAngle);
    lastMoveTime = millis();
    Serial.println(servoAngle);
  }
}

I had some physical difficulty adjusting the header pins, but a pair of pliers solved it. I also couldn’t get the Servo working for several minutes, because I’d tried wiring its power into the side rail power instead of the 5V output direct from the Arduino. A few lessons learned, as always!

I noticed the motor doing a lot of minor jittering from the rapidly-fluctuating analog input. To reduce wear & tear on the motor, I found Arduino’s sensor smoothing tutorial, which I retrofitted into my code:

#include "Servo.h"
 
Servo servoMotor;


const int numReadings = 10;


int readings[numReadings];      // the readings from the analog input
int readIndex = 0;              // the index of the current reading
int total = 0;                  // the running total
int average = 0;                // the average
 
void setup() {
  Serial.begin(9600);
  servoMotor.attach(9);


  // initialize all the readings to 0:
  for (int thisReading = 0; thisReading < numReadings; thisReading++) {
    readings[thisReading] = 0;
  }
} 
 
void loop() {
  // subtract the last reading:
  total = total - readings[readIndex];
  // read from the sensor:
  readings[readIndex] = analogRead(A0);
  // add the reading to the total:
  total = total + readings[readIndex];
  // advance to the next position in the array:
  readIndex = readIndex + 1;


  // if we're at the end of the array, wrap around to the beginning:
  if (readIndex >= numReadings) {
    readIndex = 0;
  }


  // calculate the average:
  average = total / numReadings;


  int servoAngle = map(average, 0, 1023, 0, 179);
  Serial.println(servoAngle);
  servoMotor.write(servoAngle);


  // delay in between reads for stability
  delay(25);
}

It worked perfectly! If you compare the sound on the videos, it’s a drastic difference in how much the motor is on for.