function sig=pwmgen(f,d,np)
%plot(pwmgen(100,0.5,4));axis([0 50 -2 2])
%f is the frequency of the pulses
%d is the dutty cycle (value from 0 to 1)
%np is the number of pulses
t=0:1e-3:np*1/f;
ton=d*1/f;
toff=(1-d)*1/f;
nton=find(((t>(toff-1e-3))) & (t<(toff+1e-3)));
ntoff=find(((t>(ton-1e-3))) & (t<(ton+1e-3)));
if ton==0, nton=0,end
if toff==0, ntoff=0,end
s=[ones(1,nton) zeros(1,ntoff)];
sig=repmat(s,1,np);
