Hi, I have written the following:

-(void) checkIfLineCollidesWithAll
{

    float slope = ((160-L1Circle1.position.y)-(160-L1Circle2.position.y))/((240-L1Circle1.position.x)-(240-L1Circle2.position.x));
    float b = (160-L1Circle1.position.y) - slope * (240-L1Circle1.position.x);
    if ((240-L1Sensor1.position.x) < (240-L1Circle1.position.x) && (240-L1Sensor1.position.x) < (240-L1Circle2.position.x) || ((240-L1Sensor1.position.x) > (240-L1Circle1.position.x) && (240-L1Sensor1.position.x) > (240-L1Circle2.position.x)))
    {
        [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorOk.png"]];
    }
    else if (slope == INFINITY || slope == -INFINITY)
    {
        if (L1Circle1.position.y + 16 >= L1Sensor1.position.y || L1Circle1.position.y - 16 <= L1Sensor1.position.y)
        {
            [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorBad.png"]];
        }
        else {
            [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorOk.png"]];
        }
    }
    else if (160-L1Sensor1.position.y + 12 >= slope*(240-L1Sensor1.position.x) + b && 160-L1Sensor1.position.y - 12 <= slope*(240-L1Sensor1.position.x) + b)
    {
        [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorBad.png"]];

    }
    else {
        [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorOk.png"]];
    }
}

Basically what this does is finds m and b in the well known equation: y = mx + b and then substitutes coordinates of the L1Sensor1 (the circle I'm trying to detect if it it intersects with the line segment) to see if y = mx + b hold true. But, there are two problems, first, when slope approaches infinity the range of what the L1Sensor1 should "react" to (it "reacts" by changing its image) becomes smaller. Also, the code that should handle infinity is not working. Thanks for the help in advanced.