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I've several of PIR sensor modules (HC-SR501) which are designed for a 5v input. However, I need it to run on a 3.3V system only. To achieve this, I removed the diode which is in series with the input power and a 7133 LDO. I then connected the output of the 7133 directly to the VIN pin.

As far as I understand, due removing this, there is no filtering of the input power. Which results in weird behavior, like triggering randomly all the time. This might be the ESP8266 which is generating noise when having the radio module active.

What would be a good way to remove this noise from the VIN of the PIR module? I tried placing a 0.1uf and 10uf ceramic capacitor close to the input pins, which didn't result in better behavior.

This is the circuit of the PIR module: enter image description here

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I did read this on the product page:

"The module does not take the load to work properly, connected to the load after the work of chaos, one reason is because the power capacity is very small load power consumption, load caused by voltage fluctuations caused by the module malfunction, the other reason is the load The power will have interference in the work, such as relays or electromagnets and another inductive load will produce a reverse electromotive force, 315M emission plate will have electromagnetic radiation and other work will affect the module. The solution is as follows: A, the power part of the inductor filter. B, using the load and the module using different voltage methods, such as: load using 24V operating voltage, the module uses 12V operating voltage, during which the use of three-terminal regulator isolation. C: Use a larger capacity power supply."

What kinds of inductor would help?

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    \$\begingroup\$ In could be RFI from the WiFi signal emitted by the ESP 8266. Does the random triggering stop if WiFi is completely disabled? If so, try adding a series inductor (RF choke) on the power line, shield the PIR module (leaving sensor uncovered), or move it farther away from the ESP8266. \$\endgroup\$ – Mark Leavitt Feb 4 at 23:04
  • \$\begingroup\$ It does not seem to help disabling the radio. However, I did read to use a inductor filter on the product page. \$\endgroup\$ – jancoow Feb 5 at 11:31
  • \$\begingroup\$ Can you point me out what kind of inductor I need to place in between? \$\endgroup\$ – jancoow Feb 5 at 21:31

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