File content as of revision 3:11c2175b4478:

#include "mbed.h"
#include "read_filter_emg.h"
//included for fabs() function
#include <math.h>

//input (u) = analogin

AnalogIn(/*pin-name*/) = &aI;
input = aI.read();

double v1=0;
double v2=0;

//general biquad filter that can be called in all the filter functions
double biquad(double u, double &v1, double &v2, const double a1,
                    const double a2, const double b0, const double b1, const double b2)
{
    double v = u * a1*v1 * a2*v2;
    double y = b0*v + b1*v1 + b2*v2;
    //values of v2 and v1 are updated, as they are passed by reference
    //they update globally
    v2 = v1; v1 = v;
    return y;
}

//Specifying filter coefficients highpass

   /* high pass filter consists of three cascaded biquads
    blow coefficients for those three biquads */
    //first high pass biquad
    const double highp1_a1 = -0.67538034389;
    const double highp1_a2 = 0.12769255668;
    const double highp1_b0 = 1.00000000000;
    const double highp1_b1 = -2.00000000000;
    const double highp1_b2 = 1.00000000000;

    //second high pass biquad
    const double highp2_a1 = -0.76475499450;
    const double highp2_a2 = 0.27692273367;
    const double highp2_b0 = 1.00000000000;
    const double highp2_b1 = -2.00000000000;
    const double highp2_b2 = 1.00000000000;

    //third high pass biquad
    const double highp3_a1 = -0.99216561242;
    const double highp3_a2 = 0.65663360837;
    const double highp3_b0 = 1.00000000000;
    const double highp3_b1 = -2.00000000000;
    const double highp3_b2 = 1.00000000000;
    
//Specifying filter coefficients lowpass

    /* lowpass filter consists of three cascaded biquads
    below the coefficients for those three biquads */
    //first high pass biquad
    const double lowp1_a1 = -1.05207469728;
    const double lowp1_a2 = 0.28586907478;
    const double lowp1_b0 = 1.00000000000;
    const double lowp1_b1 = 2.00000000000;
    const double lowp1_b2 = 1.00000000000;

    //second high pass biquad
    const double lowp2_a1 = -1.16338171052;
    const double lowp2_a2 = 0.42191097989;
    const double lowp2_b0 = 1.00000000000;
    const double lowp2_b1 = 2.00000000000;
    const double lowp2_b2 = 1.00000000000;

    //third high pass biquad
    const double lowp3_a1 = -1.42439823874;
    const double lowp3_a2 = 0.74093118112;
    const double lowp3_b0 = 1.00000000000;
    const double lowp3_b1 = 2.00000000000;
    const double lowp3_b2 = 1.00000000000;
    
//input to each filter is output of the filter before(excl. first which uses input_sample)
    /* NOT SURE IF PASSING V1 AND V2 IS CORRECT,
    WILL IT UPDATE IN THE MEMORY POSITION SO THAT
    V1 IS CHANGED GLOBALLY */
    
//highpass

double highpass_filter(double input)
{
    double y1 = biquad(input, v1, v2, highp1_a1, highp1_a2, highp1_b0, highp1_b1, highp1_b2);
    double y2 = biquad(y1, v1, v2, highp2_a1, highp2_a2, highp2_b0, highp2_b1, highp2_b2);
    double y3 = biquad(y2, v1, v2, highp3_a1, highp3_a2, highp3_b0, highp3_b1, highp3_b2); 
    
    return y3;
}
    
    
//rectifier
double rectify(double y3)
{
    y3 = fabs(y3);
    return y3;
}

//lowpass

double lowpass_filter(double y3)
{
    double y4 = biquad(y3, v1, v2, lowp1_a1, lowp1_a2, lowp1_b0, lowp1_b1, lowp1_b2);
    double y5 = biquad(y4, v1, v2, lowp2_a1, lowp2_a2, lowp2_b0, lowp2_b1, lowp2_b2);
    double filtered_signal = biquad(y5, v1, v2, lowp3_a1, lowp3_a2, lowp3_b0, lowp3_b1, lowp3_b2);
    
    return filtered_signal;
}

double filter(double input)
{
    /* function passes the input through the three filters
    returns the final output value as filtered sample
    this is used in check_state() function to determine state of system
    */
    double y1 = highpass_filter(input);
    double y2 = rectify(y3);
    double filtered_signal = lowpass_filter(y3);

    return filtered_signal;
}