function plotsine(freq, ampl, duration)
% plot a sine wave
% freq: frequency of the sinewave in Hertz
% ampl: amplitude of the sinewave
% duration: duration of the sinewave in seconds
step = 0.01/freq;
time = 0:step:duration;
sine = ampl*sin(2*pi*freq*time);
if duration <= 1.0
	plot(1000.0*time, sine);
	xlabel('Time [ms]');
else
	plot(time, sine);
	xlabel('Time [s]');
end
ylim([-1.2*ampl 1.2*ampl]);
ylabel('Sinewave');
title(sprintf('Frequency %g Hz', freq));
end