Author Topic: PIR Problem disappear when probing  (Read 536 times)

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Offline fedimakniTopic starter

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PIR Problem disappear when probing
« on: May 25, 2020, 09:35:27 am »
Hello,

I am currently facing really weird problem
I am using a PIR sensor panasonic one EKMB1300100K
I have an LED which blink when it detect movement. The problem here that it keeps blinking always but when i probe with the oscilloscope at the PIR pin exactly the problem disappear and return to work normally, even after removing the probe it keeps working ( removing the power and power on again also work fine ) The probelm only at the startup. I tried 5 PCBs with the same config and all of them have the same behavior.

I want to fix this problem if someone have any solution please do not hesitate.
Thanks
 

Offline floobydust

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Re: PIR Problem disappear when probing
« Reply #1 on: May 25, 2020, 08:50:27 pm »
After power up, it takes 30 seconds for the PIR sensor to stabilize. So during startup, the sensor will not work well. Try wait a while before doing your tests.

The Panasonic modules have very low output current (FET source) 100uA and needing a pulldown resistor. It's not enough current to drive an LED without adding a transistor. Drawing more than 100uA can cause false triggers.
The sensors also need clean power, so your scope ground might be affecting electrical noise if the sensor has a weird power supply. Or the probe capacitance is affecting your output.
If you want more help, post your schematic.
 

Offline Kasper

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Re: PIR Problem disappear when probing
« Reply #2 on: May 26, 2020, 04:06:18 am »
PIR circuits sometimes use high value resistors.  So high that the resistance of your scope can effect your circuit

Try replacing your scope probe with a 10 M ohm resistor.  Try with a 1 M ohm also. 

When you add that resistor to your circuit, does it behave the way it does when you add the scope probe to it?

If it does then try adding it to your schematic and think about what effect that has.
 


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