int x;
float f;
void main()
{
	while(1)
	{
		printf("Press START\n")
		while(!start_button())
		{}
		reset_system_time();
		while(stop_button()==0 && mseconds()<(long)20000)
		{
			x=knob();
			printf("knob is at %d\n", x);
			f=(float)x+150.;
			tone(f,f/1000.);
		}
	}
}