Generate sine signal in C without using the standard function

Question

I want to generate a sine signal in C without using the standard function sin() in order to trigger sine shaped changes in the brightness of a LED. My basic idea was to use a lo

Answer 1

I would go with Bhaskara I's approximation of a sine function. Using degrees, from 0 to 180, you can approximate the value like so

float Sine0to180(float phase)
{
    return (4.0f * phase) * (180.0f - phase) / (40500.0f - phase * (180.0f - phase));
}

if you want to account for any angle, you'd add

float sine(float phase)
{
    float FactorFor180to360 = -1 * (((int) phase / 180) % 2 );
    float AbsoluteSineValue = Sine0to180(phase - (float)(180 * (int)(phase/180)));
    return AbsoluteSineValue * FactorFor180to360;
}

If you want to do it in radians, you'd add

float SineRads(float phase)
{
    return Sine(phase * 180.0f / 3.1416);
}

Here is a graph showing the points calculated with this approximation and also points calculated with the sine function. You can barely see the approximation points peeking out from under the actual sine points.