File content as of revision 0:3e6ae21a6bb1:

/* PIservo
 implement a PI controller with USB serial gain setting to stabilize dipole trap power.
 Two analog inputs (control and sensor), one analog output (to RF VCA).

20120806 Andreas Steffen
*/


#include "mbed.h"

AnalogIn ctl(p20);
AnalogIn pd(p16);
AnalogOut vca(p18);
DigitalOut led1(LED1);
Serial pc(USBTX, USBRX);


Timer t;
Ticker commTick;
Ticker intTick;

float pGain = 1.;
float iGain = 1000.;
float integrator = 0.; //the building up integrator value

void serialComm(){
    char c;
    float f;
    
    if (pc.readable()) { 
        c = pc.getc();
        pc.scanf("%f", &f);
        switch (c) {
            case 'p':
                pGain = f;   
                pc.printf("Changed p gain to %f.\n",pGain);
                break;
            case 'i':
                iGain = f;   
                pc.printf("Changed i gain to %f.\n",iGain);
                break;
            default:
                pc.printf("Command not understood.\n",iGain);
                pc.printf("Read %c and %lf.\n",c,f);
                break;
        }
    }
}

void limitIntegrator(){ 
    if (integrator > 3.3) {
            integrator = 3.3;
        }
    if (integrator < -3.3) {
        integrator = -3.3;
    }
}

int main() {
    float err;
    pc.printf("mbed restarted!\n");
    
    commTick.attach(&serialComm,0.5); //check serial every half second  
    intTick.attach(&limitIntegrator,0.001); //check integrator overrun every ms  
    
    t.start();

    while(1) {
        err = ctl - pd;  
        integrator += err * iGain*1e-6 * t.read_us(); //iGain is in Hz!
        t.reset();  //reset timer to get next integration time      
        vca = err * pGain + integrator;        
    }
}