1. amplify and output the square wave from 8051 pin. make this sq. wave frequency increasing with time. say df/dt is rate of frequency change with time t.

2. mix the echo with your current freq and measure the difference. d= ft-f0. this differerance increases with time. let the differnace between the current freq and echo freq is dF = t1.df/dt, where t1 is the time taken in traveling twice the distance you are measuring i.e.

t1=2D/C (speed of sound in the medium).


=> dF = 2D/c*df/dt


df/dt can be calculated by the distance you wanna measure. if you start from the freq 'f0' and finish at fmax then sound wave echo should be available well before we reach fmax. once reaching fmax.


thats an instant idea and no guaruntee for it. may be and may be not.


abhishek