Then it's more than likely either a photodiode or a phototransistor.
Can you post a schematic of the circuit you played with?
A different kind of motion sensing security light?
Feb 03, 2013
49 Replies
I've done long-range PIR detection before and 20 feet is pretty easy,
but 100 feet is going to take some care.
Can you tell us a little more about your application?
Google produces 280 results for my "Tonal Voltmeter". I'm sure it was just that, using a photodiode to vary resistance/voltage. It looked like a clear T1 LED. I have nothing left (except fond memories) from experimenting with electronics.
eternalseptember.org, huh?
Bye.
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properly
sci.electronics.design:267761 sci.electronics.basics:34918
>
If you mean PIR motion detectors, they usually have twin element pyrometers (thin film thermistor) a motion of a IR source (person) is "grated" to produce a gross change from one element to the other - this is done in various ways such as Freznel type lenses (special IR transparent material) and faceted surface reflecting reflectors.
Most of the examples I pulled apart and hand traced the circuit years ago, were based on the LM324.
That's strange that you would call them thermistors? TO me a thermistor is a slow reacting device? But yet we have an application where we use a basic pyroelectric 3 wire detector for detecting vibration of small conductor as it exits from an induction heater. This vibration can get up to around 1khz or more when the wire snaps for what ever reason.
I would think a thermistor device would be a little slow for this wouldn't you?
Maybe the units I used have different smoke in side.
Jamie
AIUI they are closer to capacitor than resistor, the device does sense its own temperature though, they detect remote temperature by black-body radiation changing the temperature of the sensor.
TO me a thermistor
if you could make it thin enough it would work.
?? 100% natural
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I have some continuity/voltage checkers with a thin film PTC in series with an inverse parallel pair of high efficiency LEDs (2mA rating) - the series PTC thermistor can react fast enough to protect the LEDs from application to voltages upto 450V.
The sensor elements aren't thermistors, which are made from sintered
metal oxides (NTC) or a doped polycrystalline ceramic (PTC).
They're made from gallium nitride, cesium nitrate, polyvinyl
fluorides, derivatives of phenylpyridine, or cobalt phthalocyanine.
Moreover, thermistors exhibit a static change in resistance with a
change in temperature, while PIR elements generate a charge when
abruptly heated or cooled below their ambient temperature.
Apples and oranges.
Your usual disingenuous self!
My point is that a thin film thermistor can have a very fast response time - there was no need to be specific exactly what material the thin film was.
Identifying the materials was necessary in order to show you that
PTC's can't be PIR sensors, and vice versa.
Whether a thin-film PTC thermistor can have a very fast response time
is irrelevant when the discussion is about PIR sensors so, as usual,
you're befuddled.
On the one hand, consider the PTC thermistor you described and, on the
other, a PIR sensor.
The PTC thermistor is designed to have its resistance increase
spectacularly as it self-heats because of small changes in the current
through it, while the PIR sensor is designed to generate a miniscule
charge when the temperatures its elements are exposed to change
abruptly, ergo apples and oranges.
Wriggle wriggle!
In which way?
Any which way it takes when caught out.
I merely point out your errors, and since you were caught out as not
knowing the difference between a thin-film thermistor and a PIR sensor
and not knowing that a Fresnel lens isn't just for use with IR, it
seems you're the one doing all the wriggling when what you should be
doing is thanking me for smartening you up a bit.
They can both be thin film - a point you're too thick to get!
This is a copy/paste of what I typed: " Freznel type lenses (special IR
Being "Freznel type lenses" they're obviously based on something that existed before PIR sensors. - the more you wriggle - the more you have to be disingenuous about what I actually said.
You're even too thick to snip what I actually said, so everyone can see you're making it up the things I never said!
Ah, but that wasn't the point.
Since you wrote:
"If you mean PIR motion detectors, they usually have twin element
pyrometers (thin film thermistor)"...
The point was that that clearly indicates you thought PIR elements
were thermistors, which they never were, aren't, and probably never
will be.
I could be wrong, of course, and if you can provide an example of a
thermistor being used as a PIR motion detector, I'll be happy to
concede the point.
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