Michael said:
Hi,
I'm looking at parking sensors and can't work out why there aren't lists of
sites on Google telling you how to make homemade versions. Surely all you
need is an array of ultrasonic sensors each one "pinged" in turn to avoid
interference and then read the distance values into a uC for
analysis........or am I missing something?
Cheers,
Michael
Just some months ago I took one apart.
One exponential horn(~1 inch cross)as transmitter, and
another such horn as receiver.
I think you can buy tweeters looking like that.
Opening angle about 120(+/-60)degrees opening angle.
Copper/ceramic disks such as in most beepers as transmitter
and receiver.
the following method was used in a kodak automatic focus camera
in the dark ages(~1975??) and obviously broke down when
photographing through a windowpane
.
Usable range was about 10m (11-12yards).
Transmit ~ 2-6 bursts per second, 1 msec long, ~20-50 KHZ.
1 msec is about 150mm(150 out,150 back,300mm/msec sound speed).
I would advice to use 3 analog multipliers to multiply
the incoming signal with the 4'thpower of time, or in other words,
use a sawtooth signal to start with, feed that to both inputs
of the first multiplier,output to the second multiplier, then feed
receiver and 4'th power sawtooth to the third multiplier.
That way your return signal strength on the timescale will be nearly
constant, only the noise will rise with increasing distance,
until the signal becomes useless.
Then trigger on that, and measure time to get distance.
Also the amplitude of your sawtooth at the trigger moment, stands
for time/distance measured.