I know there is a circuit there but there is no explanation of it whatsoever and I'm not that experienced to know how this works and if it does what I want. Since it switches a relay then it's final output is binary. Either on or off. I need an output that gives off values between 0 and 5 volts. Since I don't know which stages do what and what to cut off I'll refrain from building it. If though no one else has a better solution to my problem I'll have to build it bit by bit and probe everything till I figure stuff out.
The circuit isn't that complicated. Just break it down into several parts.
C9 to C14 and R8 to R10 form a power supply filter.
ZD1 regulates the voltage to the PIR and all of the biasing circuitry. U1's power supply isn't shown, but I believe it's connected straight to +12V, as the zener regulator won't provide power for it.
U1-A is a non-inverting amplifier, with some filtering. Its gain is determined by R3 & R4 and the passband by C3 to C4.
U1-B is an inverting amplifier, again with some filtering. Its gain is set by R11 and R5 and the passband by C8 & C5.
U1-C, U-D, D1 & D2 form a window comparator, with the voltage thresholds set by R12 to R13. As mentioned above it's required to activate the relay.
If you just want an analogue signal, then take the output from U1-B. The circuit can be simplified by using the LM358, which is the same as the LM324, but with only two op-amps.
Search for op-amp inverting/non-inverting amplifier and window comparator, for more information.
