I need to make a PIR motion sensor for a museum project. The plan is that the PIR activates sounds when visitors enters certain displays/exhibits.
I choose for the following solution, since it is a project that has been made with simple components, tested and proven functionally.
To my great frustration it did not work as expected!
The circuit is way too insensitive. Only moving my soldering iron closely to the PIR activated the circuit. My hand didn't do anything.
Therefore I started to change things.
I tried 2 different PIR sensors, one from eBay, the other one salvaged from a professional alarm system. Same result.
R1 was changed into 1K, resulting in a slight increase of sensitivity.
I changed R3 into respectively 2M and then 1M, but the circuit was unstable and prone to oscillations. And when stable it was still way too insensitive.
I tried to change C2 and C3 to 100nF in order to try to get rif of the oscillations, but without success.
I did not use the LM324 as in the original circuit, but choose the LM358 because that makes it easier to design the PCB. I assume these to be similar enough that this cannot be the problem. I tried several other opamps, all with the same or worse result.
I can see on the scope that moving my hand in front of the PIR gives a pulse on pin 7 of U1b. The soldering iron gives a huge pulse.
Now a few questions.
What is better: decreasing R1 as opposed to increasing R2?
Was it OK to replace the LM324?
Can the problem be the window comparator?
What else can I have done wrong???
I hope somebody can help me!
Ron Werner
Norway
I choose for the following solution, since it is a project that has been made with simple components, tested and proven functionally.
To my great frustration it did not work as expected!
The circuit is way too insensitive. Only moving my soldering iron closely to the PIR activated the circuit. My hand didn't do anything.
Therefore I started to change things.
I tried 2 different PIR sensors, one from eBay, the other one salvaged from a professional alarm system. Same result.
R1 was changed into 1K, resulting in a slight increase of sensitivity.
I changed R3 into respectively 2M and then 1M, but the circuit was unstable and prone to oscillations. And when stable it was still way too insensitive.
I tried to change C2 and C3 to 100nF in order to try to get rif of the oscillations, but without success.
I did not use the LM324 as in the original circuit, but choose the LM358 because that makes it easier to design the PCB. I assume these to be similar enough that this cannot be the problem. I tried several other opamps, all with the same or worse result.
I can see on the scope that moving my hand in front of the PIR gives a pulse on pin 7 of U1b. The soldering iron gives a huge pulse.
Now a few questions.
What is better: decreasing R1 as opposed to increasing R2?
Was it OK to replace the LM324?
Can the problem be the window comparator?
What else can I have done wrong???
I hope somebody can help me!
Ron Werner
Norway