controlling servo with compass

Projects Programming
1

|Im just new to the arduino world. but having lots of fun! im trying to turn a servo based on compass orientation. I've been trying to get this bit of code i found to work but no luck! servo just twitches every once in a while whether compass moves or not. I've tested servo it works fine and compass works fine. but with this code i don't even get any serial data streaming. anybody have any ideas to help out a newbie?

#include <Wire.h>
#include <HMC5883L.h>
#include <Servo.h> 

#define SERVO  9
#define CENTER 100
#define GOAL   0

HMC5883L compass;
int      goal = GOAL;
float    declinationAngle = 0.212;    // Radians
Servo    myservo;


void setup() {
 
 
 Serial.begin(9600);
 myservo.attach(SERVO);
 Wire.begin();
 compass = HMC5883L();
 // Set scale to +/- 1.3 Ga
 int error = compass.SetScale(1.3);
 if (error != 0)
   Serial.println(compass.GetErrorText(error));
 // Set measurement mode to continous
 error = compass.SetMeasurementMode(Measurement_Continuous);
 if (error != 0)
   Serial.println(compass.GetErrorText(error));
}

void loop() {
 
int angle = getDegrees();
 int error = goal - angle;
 if (error >= 180)
   error -= 360;
 if (error <= -180)
   error += 360;
 // Update servo and keep with range of +/- 60
 if (error > 60)
   error = 60;
 if (error < -60)
   error = -60;
 myservo.write(CENTER + error);
 delay(10);
}

int getDegrees () {
 MagnetometerScaled scaled = compass.ReadScaledAxis();
  // Calculate heading when the magnetometer is level, then correct for signs of axis.
 float heading = atan2(scaled.YAxis, scaled.XAxis) + declinationAngle;
 // Correct for when signs are reversed.
 if(heading < 0)
   heading += 2 * PI;
 // Check for wrap due to addition of declination.
 if(heading > 2 * PI)
   heading -= 2 * PI;
 // Convert radians to degrees for readability.
 return (int)  (heading * 180 / M_PI); 
}
2 
int angle = getDegrees();

What IS angle?

int error = goal - angle;

What IS error?

but with this code i don't even get any serial data streaming.

Because the ONLY Serial.print() statements are in setup(), and only for errors, which, presumably, are not happening.

3

Hi,

Can you please post a copy of your sketch, using code tags?
They are made with the </> icon in the reply Menu.
See section 7 http://forum.arduino.cc/index.php/topic,148850.0.html

Also how are you powering your project, via the USB or externally.

Tom.... :slight_smile:

4

Why don't you print the values from the compass so you can see if that is working properly ?

How many degrees can your servo rotate ?
Most of them only do about 180 deg. What should happen if the compass is pointing in a direction that the servo cannot reach ?

...R

5

I started off by powering the servo from the arduino. Which worked fine with other sketches. But just to eliminate that as a issue I powered it with a 5v adapter and connected the negative to the Arduino ground as well. Same results as before.

I apologize I will post code proper way when back on the computer.

This code is to keep servo pointed north. So a full revolution shouldn't be a problem. For now I would be happy to have any movement

Thanks

6

greenkarson:
For now I would be happy to have any movement

Are you getting valid data from the compass?

If not, there is no point worrying about anything else.

...R

7

im getting good data from compass with other sketches without changing wires so i know that its not the compass

8

It might also be reasonable to give your servo more than 10 milliseconds to move to its new position. I would be inclined to set that delay to 1000 and see what happens.

9

greenkarson:
im getting good data from compass with other sketches

Are you SURE you are getting good data with the sketch that has a problem ?

...R