sanjeev wrote:
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I want to say was that it's not only the motion the the PIR sensors senses but a lot more dont you think a combination of electro-optical could enable measurements upto radiator displacement of about tenths of second of arc? I have also seen span and ofset errors creeping in randomly do you have any idea why that happens?

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Sanjeev,

I think that the PIR is best handled in analog and that it makes a fine inexpensive, detector for low security application. I believe the analog circuitry just takes the sum-intensity voltage level and intergrates or differentiates it to get a trigger output when its changing quickly. So what is getting its attention is a rapid change in intensity over time (human motion rates) and not any particular trigger voltage levels. And you want to make sure it isn't set off by a dark room being illuminated or vice-versa.

The errors creeping in that you mentioned would effectively be removed by using the analog circuitry I mentioned. Analog is not my area of expertise.

I doubt that the PIR would be much good going through an ADC into an 8051 because to catch the changes you need the analog integrator or differentiator. The ADC would have to be high resolution and the 8051 would have to be fast and attentive to do the job. How can you justify loading an 8051 to do that?

I think a better application for the 8051 is to hook it to a CCD camera and do actual intelligent pixelation motion detection. That's a higher level of security detection and a better fit for an 8051.

aka j