Jewel Box Servo Meter

Good accuracy and linearity.

// DS_ServoMeter

// Karl Berger W4KRL

// April 27, 2014

// Released into the public domain

// Converts a 0 to 5 Volt signal into a corresponding

// position on a servo. The servo command is smoothed to

// reduce jitter.

// Uses SimpleServo in the DigiSpark library by

// Benjamin Holt

#include <SimpleServo.h>

//create a servo object

SimpleServo myservo;

// The analog input signal is connected to P2

// For pin mapping see:

// http://digistump.com/wiki/digispark/tutorials/pinguide

const int kAnalogInputPin = 1;

// connect the servo signal line to P5

const int kServoPin = 5;

// Most servos are rated for 180 degree span but may be non-linear near

// the extremes. A meter span of 120 degrees or less is more reliable.

const int kScaleSpan = 120;

// 4 samples provides good smoothing. More will slow the response.

// Less will increase jitter.

const int kSmoothingSamples = 4;

//int smoothed_val = 0;

// attach the servo to a pin then exercise it

void setup(){

myservo.attach(kServoPin);

ExerciseServos();

}

// read the analog signal, smooth it and convert it to a position

// in degrees for display by the servo

void loop(){

// static variables retain their value between function calls

static int smoothed_val = 0;

// read the input voltage

int val = analogRead(kAnalogInputPin); // this is pin P2

// smooth the value by keeping a moving average

smoothed_val = smoothed_val + ((val - smoothed_val) / kSmoothingSamples);

// rescale val to the meter span

val = map(smoothed_val, 0, 1023, 0, kScaleSpan);

//command the servo to the corresponding position

SetServo(val);

//add some delay to let the servo seek its position

delay(15);

}

//adjust the motion of the servo to match the actual

//position to the command

void SetServo(int val)

{

const int kServoZero = 20;

const int kServoFullScale = 150;

int pos = map(val, 0, kScaleSpan, kServoZero, kServoFullScale);

myservo.write(pos);

}

//Position at zero and full scale to check calibration

void ExerciseServos(){

const int kDwell = 1000;

SetServo(0);

delay(kDwell);

SetServo(kScaleSpan);

delay(kDwell);

SetServo(0);

delay(kDwell);

}

Added some detail to the construction and adjustment steps.