Diff: emg.cpp

Revision:

0:850bf2d90868

Child:

2:02d31a0caac1

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/emg.cpp	Wed Oct 25 12:35:29 2017 +0000
@@ -0,0 +1,44 @@
+#include "emg.h"
+
+emg_shield::emg_shield(PinName pin,float fs):emg_in(pin)
+{
+    highpass.a=0.05;                                // filter coefficient of high-pass filter
+    float lambda= 51.6    *2.0*3.1415;                    // 50 Hz notch filter frequency in rad/s (Hz*2*pi)
+    float b= 4.0          *2.0*3.1415;                    // 50 Hz notch filter bandwidth in rad/s (Hz*2*pi)
+    notch50.lambda = lambda/(2.0*fs);               // scaling for the 2/T multiplication which happens in the transform from s-domain to z-domain
+    notch50.b = b/(2.0*fs);                         // scaling for the 2/T multiplication which happens in the transform from s-domain to z-domain
+    float lambda2=103.2   *2.0*3.1415;                    // 100 Hz notch filter frequency in rad/s (Hz*2*pi)
+    float b2= 4.0         *2.0*3.1415;                    // 100 Hz notch filter frequency in rad/s (Hz*2*pi)
+    notch100.lambda = lambda2/(2.0*fs);             // scaling for the 2/T multiplication which happens in the transform from s-domain to z-domain
+    notch100.b = b2   /(2.0*fs);                    // scaling for the 2/T multiplication which happens in the transform from s-domain to z-domain
+    float wc = 10        *2.0*3.1415;                    // butterworth filter cutoff frequency in rad/s (Hz*2*pi)
+    butter.w = wc/(2.0f*fs);     
+    Value=0;
+    butter.yprev[0]=0;
+    butter.yprev[1]=0;
+    butter.xprev[2]=0;
+    butter.xprev[0]=0;
+    butter.xprev[1]=0;
+    tick.attach(this,&emg_shield::tickFunction, 1.0f/fs);                    
+}
+
+void emg_shield::tickFunction(){
+    float raw_data = emg_in.read();                           // obtain raw EMG data
+    
+    float emg_notch = notch50.filter(raw_data);               // notch filter to filter out the noise (especially from laptop charger)
+    
+    float emg_hp = highpass.filter(emg_notch);              // high-pass filter
+      
+    float emg_hp_abs = fabs(emg_hp);                        // full wave rectification
+    
+    //float emg_envelope = lowpass.filter(emg_hp_abs);        // 2 1st order low-pass filters
+    //emg_envelope = lowpass2.filter(emg_envelope); 
+    float emg_envelope = butter.filter(emg_hp_abs);       // or 1 2nd order (butterworth) low-pass filter
+    
+    Value = emg_envelope;
+}
+
+float emg_shield::GetValue(){
+    return Value;
+}
+