A different kind of motion sensing security light?

Correct me if I'm wrong on any of this, but... The motion sensor (part) output constantly varies. Only when its output reaches a certain level relative to its normal state, then it trips a switch that drives the light for some period of time. Then the lightbulb switches off and waits for another significant change in detection.

What I would like to do is have a lightbulb or LED brightness/intensity follow the motion sensor output part. In other words... If a bird flies by, the lightbulb would momentarily dimly light. If a person walks into close range, the lightbulb would continuously shine brightly. If the person walked behind some object, the lightbulb would go off, and then when they reappeared, the lightbulb would come back on. Hopefully I'm not over describing this, but I'll be happy to provide more description if asked.

Does such a device (or close) already exist for purchase in a store?

The sensor output part typically could not be connected to an LED without putting an amplifier on it? Anybody do this before, any schematic?

Thanks.

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Reply to
John Doe
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look at ultrasonic distance sensors. You can get outputs that are analog for a distance reading of an object infront of it or a switched output when an object is with in range.

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Jamie

Reply to
Jamie

AFAIK, pyroelectric sensors are a "single pixel" sort of thing, so they don't know if the scene is moving, only if the average IR changes. Which it does when someone comes into view or jumps out of the shadows, but it doesn't do jack if someone walks around freely while holding up a room-temperature blanket, or moves in the scene while presenting an equal viewing cross section (probably tricky to do).

The output is positive or negative charge, corresponding to the change in temperature viewed. Into a high resistive load (say, like something Phil might be working on right now :) ), this has a time constant (the sensor's just an insulating crystal), so it automatically centers after a while. In other words, it's a temperature differentiator (for pedants, that's the RC kind). Obviously, a motion detector needs only a window comparator; you could use a suitably calibrated gain instead (followed by a full-wave active rectifier), and maybe a lowpass, or falling slew rate limiter, to enhance the effect.

Still might not be quite as intended; if the detector response is equal across the viewing angle, then a person walking across the path will cause it to light up (or down), then not do so much (depending on how the sensor sees a walking body), then light up again on leaving the frame.

Tim

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Reply to
Tim Williams

That's all I want. It's not going to be the only part of the system, and I can interpret the output. I guess it could even be a very short (1 second or less) on time by a common passive infrared motion detector, so that it would flash during its detection time.

Reply to
John Doe

I don't know about this particular sensor, but most of the commercial PIR elements for porch lights have the FET built in. Maybe the 47k is the source resistor of the JFET follower?

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

You can buy sensors that have a restricted/adjustable "target" size. To eliminate nuisance operations from small animals.

There will always be an amplifier and relay in the circuit.

Reply to
harry

I doubt he's going to find a finished product that does what he wants. The products ready to be mounted have not only the sensor, but as he points, out the circuitry that turns it into some kind of on/off output that is needed for the product.

However those motion detector products use ICs which he can probably find. Some of the ICs provide an analog output that he could use together with his own circuit. Here are examples from one company:

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Reply to
trader4

text -

Wrong yet again. harry is like a cosmic black hole of ignorance, no real knowledge can exist anywhere near him.

Reply to
trader4

They're two "pixels" in an AC coupled differential circuit. The optics are set so that the sensors see adjacent areas and react to fast changes. (You can fool them if you move real slow).

The best analogy of the optics is to spread your fingers apart and put the flat of your palms together so that the fingers interleave. One sensor per "hand", with the views of the two sensors interlinked. Any movement quick enough, and one sensor will decrease while the other increases. The response is usually flat in one plane, determined by the way the plastic lens is molded.

Radio-Electronics/Electronic Now magazine had a long distance pyroelectric sensor project that used a motor driven mechanical chopper, back when these things were new.

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

Reply to
Mark Zenier

On Page 3 of that brochure there's a schematic like the one I'm talking about--the sensor load resistor is inside the capsule, and the external resistor is the source load for the JFET follower. That's the usual approach IME.

Porch light sensors are actually pretty cool devices--they use a split pyroelectric sensor, with the two halves wired opposing each other. A segmented Fresnel lens casts a dozen or so images of the scene, so as you walk up to the door, a dozen of you cross the sensor, causing about a 10- or 12- cycle AC waveform, which is detected with a comparator.

The split cell makes the sensor much more resistant to changes in ambient temperature, power supply voltage, and that sort of stuff. A cute design--whoever came up with it should be better known.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

we used a few of those for wire break and jerk detectors just as the conductor comes out of the induction heater and prior to entering the extrusion head assembly.

Since the conductor will jerk with a over sized section going through or a breakage, it works out well. There is also a small air jet that sits infront of the IR passive glass to keep the dust off.

Jamie

Reply to
Jamie

One must also be *VERY* careful when handling/installing the device as well. They usually come with shorting wires on the leads they are so worried.

Some FETs can be blown by an ESD field, particularly prior to being installed. Does not even require contact.

That is why a smock is required at the 'proper' ESD safe workstation. It 'contains' whatever fields you and your insulative clothing may be carrying.

Reply to
SoothSayer

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Generally, no. 

The common pyroelectric motion sensor outputs a single pulse when the 
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Reply to
John Fields

I guess that means there is no analog output. So it's not like a photo resistor. I've played with photo resistors, controlling a variable frequency connected to a speaker. Aiming it towards a TV produced amusing and rapidly changing frequencies. I wonder if there are hypersensitive photo resistors that might do (with a wide field of view), maybe infrared or whatever. Or maybe that has already been suggested under different terminology.

I don't need to know distance or speed. All I want to sense is changes in radiation in the area. But if the changes in intensity are great, that might suggest the object is either large or nearby. I guess that would be a function of something like a long-range omnidirectional (or wide angle, as long as it's view is not narrow) infrared photo resistor/sensor if there is such a thing. I'll look.

Distance to sense a person, to noticeably and distinctly change the output, needs to be at least 20 feet, preferably 50-100.

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Reply to
John Doe

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Reply to
mike

To be clear... actually, what I played with might be called a photodiode (not a photoresistor), it looked like an ordinary white LED, it didn't have the squiggly wires inside

Reply to
John Doe

FWIW... I will plan to use that, that will be easiest. I will see if the output can be made to flash a light as long as motion is being detected, without a long delay or long on-time.

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Thanks to the replies.
Reply to
John Doe

these sensors detect movement by having two "pixels" that are focused by the lens onto alternating bands of the scene, the sensors only produce a signal proportional to the rate of change of average temperature of the area viewed by the pixel.

a person walking across the fiels od view would produce a signal that alternates between the two sensors.

I've not heard of one.

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Reply to
Jasen Betts

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If you're going mechanical, why not make it a capacitive sensor. Chopping the field from the intruder. Since you kknow the speed of the chopping, you can synchronously detect and obtain EXACTLY the type of signal you want. ...I think.

Reply to
Robert Macy

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John Fields

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