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PIR sensor schematic understand

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yassin.kraouch

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Can anyone explain to me the schematic in page 10 **broken link removed** ?
because in PIR sensor there are two kind circuit, directly using IC and using discrete component,
what is the best choice ?
many thanks,
 

NJM2903 is a comparator, NJM2904 is an opamp. Using the NJM2904 circuit you could use a quad opamp. Using a comparator for the outputs will give a better output voltage range.

Keith
 

Audioguru said:
Maybe the datasheet is missing an English explanation from the original Japanese document.
Click to expand...
can you please do some explanantion if you understand ? or if you have the japanese version, can you please upload it ?
thanks
 

What don't you understand about the circuits and the differences?

Keith
 

keith1200rs said:
What don't you understand about the circuits and the differences?

Keith
Click to expand...
i did not how it works, i am not so familar with operational apmplifier, thats why i have difficulties to understand it,
i need to understand it and be able to design my own circuit,
why we need this circuit ? it is not possible to connect the S signal of the PIR to a MOSFET ? or a microcontroller ?
 

The circuit is essentially a bandpass amplifier (0.3 - 1.3 Hz) with a gain of about 30000, followed by a comparator. The input referred switching threshold is in a 10 µV range.

If you know how to achieve a similar sensitivity with discrete transistors or a microcontroller (it's possible of course), then you can design an alternative circuit.

Seriously speaking, I forsee some difficulties with no substantial knowledge of analog circuits or Pyroelectric sensor operation.
 
Last edited:

we have three schematic in the file from murata, which one i have to follow (Human Detection, Analog out Typeor Comparator out Type) ??
i want to detect the presence of human, and put ON/OFF a transistor,
 

Your main problem is essentially no basic knowledge of the components and circuits involved. We can guide you but then you will repeat the same questions and learn nothing.
Start reading a basic course on electronics. Find the ARRL Radio Amateur Handbook, one of the best for everyone
 

jiripolivka said:
Your main problem is essentially no basic knowledge of the components and circuits involved. We can guide you but then you will repeat the same questions and learn nothing.
Start reading a basic course on electronics. Find the ARRL Radio Amateur Handbook, one of the best for everyone
Click to expand...
no i have knoledga on basic electronic, but if it will be complicated than it is difficult for me to understand,
 

The three circuits are all slight variations of the same thing. The "Comparator out Type" is probably the most appropriate for what you want.

Keith
 

thanks keith, can you please explain to if a human is detected how the circuit works ?
i am not asking about electronic basics but how all circuit work together
 

FvM already gave a description
The circuit is essentially a bandpass amplifier (0.3 - 1.3 Hz) with a gain of about 30000, followed by a comparator. The input referred switching threshold is in a 10 µV range.
Click to expand...

The PIR detectors rely on varying infra-red not absolute levels. For this to work they need a lens system in front of the sensor (usually a fresnel lens). As you move in and out of the zones seen by the detector (and created by the fresnel lens) the infra red from the body will rise and fall. The circuit detects these changes.

Keith
 

The signal from PIR sensor is amplified and filtered by LM358 -> comparator -> LM555 is used as monostable circuit with time constant which is written below the schematic. I think that this is too complicated circuit for basic application
 

keith1200rs said:
FvM already gave a description

The PIR detectors rely on varying infra-red not absolute levels. For this to work they need a lens system in front of the sensor (usually a fresnel lens). As you move in and out of the zones seen by the detector (and created by the fresnel lens) the infra red from the body will rise and fall. The circuit detects these changes.

Keith
Click to expand...
i want to made a prototype of this circuit,
how can i verify if my circuit will work or not ?
cna i run simulation using ltspice for example ?
many thanks
 

why in teh schamatic we have everytime a capacitor i nseries with the amplifier ?
 

Usually, a high gain AC amplifier will be AC coupled.

The series capacitors are also making half the high pass part of the bandpass characeristic.
 

i gues that the capacitor block DC signal and also form a high pass filter, right ?
 

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