The proposed solution to the
problem of developing an inexpensive altimeter was to create a sonic pulse
altimeter. Using a speaker and microphone combination, a sonic pulse can be
generated, reflected off the water surface and captured by the microphone. The
measurement of the time delay between the original pulse (ping) and the
received echo can then be used to calculate the altitude by using the following
equation:
where Δt = time between signal
and echo, d = distance, and c = the speed of sound (approximately 343 m/s).
In order to realize this solution in real time and maintain timing accuracy, a microprocessor would be required to control the generation of the ping pulse and the reception of the echo. The ping signal would then drive a speaker, with the echo being received by a microphone. Once received, the signal would need to be filtered and amplified in order to discriminate the echo from the ambient noise. Finally, the microprocessor would be used to accurately determine the elapsed time interval between the transmission of the ping and the reception of the echo. Using this time, it could calculate the distance traveled and display this on an LCD screen or other appropriate display in the airplane cockpit.