iPhone Accelerometer calibration

Question

How do I properly calibrate the accelerometer for my iPhone game? Currently, when the phone is on a flat surface, the paddle drifts to the left. High or Low Pass filters are not an acceptable solution as I need complete control over the paddle even at low & high values. I know Apple has the BubbleLevel sample but I find it difficult to follow... could someone simplify the process?

My accelerometer code looks like this:

-(void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration {

float acelx = -acceleration.y;
float x = acelx*40;

Board *board = [Board sharedBoard];
AtlasSprite *paddle = (AtlasSprite *)[board.spriteManager getChildByTag:10];

if ( paddle.position.x > 0 && paddle.position.x < 480) {
    paddle.position = ccp(paddle.position.x+x, paddle.position.y);
}

if ( paddle.position.x < 55 ) {
    paddle.position = ccp(56, paddle.position.y);
}

if ( paddle.position.x > 435 ) {
    paddle.position = ccp(434, paddle.position.y);
}

if ( paddle.position.x < 55 && x > 1 ) {
    paddle.position = ccp(paddle.position.x+x, paddle.position.y);
}

if ( paddle.position.x > 435 && x < 0) {
    paddle.position = ccp(paddle.position.x+x, paddle.position.y);
}
}

Thank you!

score 9 · Accepted Answer · edited Aug 30 '12 at 03:50

9

Okay, problem SOLVED and the solution is so simple I'm actually embarrassed I didn't come up with it sooner. It's as simple as this:

In a "Calibration Button":

//store the current offset for a "neutral" position
calibration = -currentAccelX * accelerationFactor;

In the game time accelerometer function:

//add the offset to the accel value
float x = (-acceleration.y * accelerationFactor) + calibration;

It's as simple as adding the offset. * hides his head *

edited Aug 30 '12 at 03:50

SimplyKiwi

12,376
22
105
191

answered Jan 22 '10 at 23:53

user2393462435

2,652
5
37
45

Here's a comprehensive explanation of the subject http://www.iphonedevsdk.com/forum/iphone-sdk-tutorials/39833-tutorial-accelerometer-calibration-optimizations.html – Alexei Sholik Nov 01 '11 at 15:56
This is an old thread but I am curious to what type of objects currentAccelX is and what accelerationFactor is. Can you assist with this? – SimplyKiwi May 11 '12 at 04:27
Yeah, where did you get those vars; currentAccelX and accelerationFactor? This post was old back in 2011...i know its even older now but perhaps someone can help me? thx – marciokoko Aug 30 '12 at 14:40
This is the code I have so far: //calibrate code from StackOverflow float calibration = -acceleration.x * accelerationFraction; float x = (-acceleration.y * accelerationFraction) + calibration; accelerationFraction = acceleration.y*2; if (accelerationFraction < -1) { accelerationFraction = -1; } else if (accelerationFraction > 1) { accelerationFraction = 1; } //API CHANGE set delegate to self if (orientation == UIDeviceOrientationLandscapeLeft){ accelerationFraction *= -1; } – marciokoko Aug 30 '12 at 14:47
1

read my explanation here: http://www.iphonedevsdk.com/forum/iphone-sdk-tutorials/39833-tutorial-accelerometer-calibration-optimizations.html – user2393462435 Aug 30 '12 at 18:29

score 0 · Answer 2 · answered Aug 30 '12 at 14:49

This is the code I have so far:

//calibrate code from StackOverflow
float calibration = -acceleration.x * accelerationFraction;
float x = (-acceleration.y * accelerationFraction) + calibration;

//My original code
accelerationFraction = acceleration.y*2;
if (accelerationFraction < -1) {
    accelerationFraction = -1;
} else if (accelerationFraction > 1) {
    accelerationFraction = 1;
}
//API CHANGE set delegate to self
if (orientation == UIDeviceOrientationLandscapeLeft){
    accelerationFraction *= -1;
}

iPhone Accelerometer calibration

2 Answers2