On 11/23/07, Jinx <joecolquitt@clear.net.nz> wrote:
> Hi Jonathan, pic_pir.gif is a circuit I use with PIR. In still air
> it will pick up a person moving at 6m. Two are used to get
> about 150 degrees coverage. Current consumption is around
> 20uA, pared down because it has to run for quite a while on
> batteries. Designs for residential security lights are usually based
> on a standard quad op-amp, as in motion_detrector.gif, (or even
> a 4000 logic chip in linear mode !), and don't have to be so mean
>
> The op-amps are used as comparators to make a logic output,
> but the analogue inputs would be measurable too, I guess, it's
> not something I need to do. As you say, the output does wobble
> about for a miniute or so, but it's quite stable after that
>
> One necessity for a good signal is to have a Fresnel lens, or
> otherwise the detection range is very short, less than a metre
> IIRC. There are different types of these lenses, eg curtain or
> specifically horizontal or vertical focus, for various end uses
>
> The elements also need to be aligned to the plane of the
> movement to be detected. In the circuit, my elements are shown
> as two vertical bars, for detecting horizontal movement. The signal
> out of the sensor is the difference between the received IR on
> each element. A stationary warm object will not set off PIR
>
> I doubt you'll be able to chase objects, because PIR is just
> too slow and coarse.

Transforming an ordinary PIR detector in a fast temperature detector
(including living object moving) is a problem of optics and mechanics.
If you will add a mechanical chopper in front of Joe's schematic PIR
detector you'll have at the output an amplitude modulated temperature
signal. Demodulate it with a simple diode (or better with an active
demodulator with OA) and voila, a fast chasing detector for an object
with large enough dimensions (like Joe) but unusefull for his mices
from the besement. Do not forget to read carefully the PIR datasheet
for choosing the radiation wavelenght sensistivity.

Vasile
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