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Re: ultrasonic update



brian whatcott wrote:

At 22:08 10/13/99 -0500, Pete wrote:
I just finished the O'scope analysis of the Ultra sonic motion detector
this afternoon.

Here's what I discovered;

The Ultrasonic frequency is 50kHz with a 50% duty cycle.
Each query consists of 17 of these pulses (350 uSec) followed by a
listen phase.
Depending on the number of queries demanded, 10 per sec, 25/sec, or
Paul's 120/sec, the pulse will have from 100 mSec (10 Hz) to 8.33 mSec
to receive the echo.
This means at 120 Hz, the maximum distance the pulse can travel and
still get back before the next pulse is 1.4 m.

Of course, the pulse may arrive during the second listen time and that
throws the whole thing off. How is it determined that the detected echo
is from the most recent ping and not some past pulse? Sounds like
another lab day to me.....

Pete Lohstreter

I hope Pete will accept these nit-picks in the spirit intended.
His use of the term 'duty-cycle' is somewhat unusual.
In radar and sonar usage, 'duty cycle' represents the part of a
repetition period occupied by the transmitted pulse.

In turn, the word 'pulse' or transmitter pulse, does not refer to
individual half cycles, but rather, the complete ensemble of
oscillations which are sent contiguously.

Using these ordinary definitions, one could describe Pete's experimental
observations like this:
Pulse time: 350 microseconds with about 17 cycles of transmitted power.
Repetition rate: 10 to 120 pulses per second.
Duty cycle:350/100000 to 350/8333 (0.35% to 4.3%)

Respectfully,

brian whatcott <inet@intellisys.net>
Altus OK

I take no offense to your comments. When I say 50% duty cycle, I mean
that each wave of the 17 transmitted are in a positive potential 50% of
the time and at ground potential the other 50%. This is opposed to some
digital signals that are only in a positive potential 10% (or some other
number)of the time. The information was to indicate the wave was
symmetrical WRT Time.

I have no problem with your explanation of duty cycle as referenced to
the entire sample cycle. I should have explained my observations more
clearly.

pete
--
Pete Lohstreter "Reality is merely an illusion,
The Hockaday School albeit a very persistent one."
Dallas, TX 75229 A.
Einstein
petel@tenet.edu
plohstreter@mail.hockaday.org
http://www.hockaday.org