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From: "Bill Sloman"
Subject: Re: Need help designing a circuit
Date: Sat, 2 Nov 2002 22:35:50 +0100
Organization: Planet Internet
NNTP-Posting-Date: 2 Nov 2002 22:35:53 GMT
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
"Neil" wrote in message
> Ok...I'm not very bright...I haven't embraced microcontrollers, and like
> do things with good old fashioned components and IC's. Keeping this in
> I need a circuit that senses the position of an object, then turns on a
> motor to power a turntable to turn toward the object. I have several P.I.R
> detectors that will be placed in the center of the turntable. So I need a
> circuit that will sense which PIR has detected the object, and then
> off once the turntable is has turned towards the direction of the sensing
> PIR.. It doesn't need to have any sort of accuracy, as long as the
> stops close to the subject(within about +/- 20 or 30 degrees). The
> switching can be either electro mechanical, or use LED Emitter/ Detectors.
> Any ideas?.
> Thanks in advance.
You don't so much need a circuit as an algorithm. You have "a couple" of
passive infra-red (PIR) sensors mounted on a turntable, and you want a
circuit which will do something when one of the PIR sensors has "detected"
You don't specify the aceeptance angle of the PIR sensors, and and you don't
specify what sort of signal the PIR sensor is producing when it detects the
object you want to detect (whatever it is).
The econimical way of doing this job is with a single sensor on a rotating
turntable - as the turnatable rotates the the single scanner scans
everything. When it "detects" something - it's output signal moves
significantly outside the range generated by random noise in the detector,
and moving non-objects in the field of view - you stop the turntable.
For more class, you rotate the turntable with a stepper motor, and don't
stop the turntable immediately, but merely note the position (or start
counting steps) and allow the turntable to continue to rotate until the
anomalous signal sinks back into insignificance, after which you reverse the
turntable back through half the number of steps, and then stop it.
Once you've got the rotating turntable, extra sensnors are a waste of time.
Advice on the sort of switches to use depends on you telling us how you
rotate the turntable, and how big the turntable actually is. My guess would
be a turntable out of a an audio system but even that covers a wide range of
Bill Sloman, Nijmegen
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