PIR Sensor is not working properly.

Joe

Hi

I have two PIR sensors and they are detecting me
very nice. But after some time they start detecting
even when I am not near them. ( Even when I am
in other room)

I used them in a completely close box
and they continue sensing about 10 times
during an hour.


I thought that a servo motor could be making
some electric noise and I turn off the servo
and all lights but I still have the problem.


Do you know why ?

Thanks, Joe

Chris Savage

Joe,

A noisy power supply could also contribute. How long are the wires from the power supply or going to the BASIC Stamp from the PIR?

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Chris Savage
Parallax Tech Support

Joe

Thanks:


How can I see a "noisy power supply" ?

Do you know where can I find information ?

About the wires , they are abot 2 feet ( 60 cm) long.

Thanks, Joe

Mike Green

2 feet is more than long enough to cause problems.

Often, the only way to "see" the noise is with a high speed scope. It's much easier to just add some filtering
to see if the problem goes away. I would suggest a 0.1uF ceramic capacitor across the power leads at the PIR.
You could add a 10uF 6V electrolytic capacitor as well or wait to see what happens with the 0.1uF capacitor.

Joe

Thanks Chris,

The PIR are working a little better now , thanks.

I forgot to tell that I have a 900 Mhz transmitter
near ( one feet) the PIR and each time
I connet the transmitter , the PIR sensors are being
difficult to read.


Do you know if can I add more capacitors or make and other
change in order to improve the PIR signal ?

Thanks, Joe

PS: the 900 Mhz transmitter output
is about 10 mW ( mili Watts ) only . The transmitter
sends video from a little camera and consumption is
about 150mA at 12 Volts

Chris Savage

One thing you can try is shielding the wires going to the PIR sensor. That might help some. In situations like this it’s difficult to find a solution without testing some ideas. Take care.

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Chris Savage
Parallax Tech Support