Re: ultrasonic update

[brian whatcott <inet@INTELLISYS.NET>]

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