PIR power down mode

bbaumgartner

I will be using a PIR to detect motion in a DARK room. Since it will be battery operated, during the day the sensor must power down to conserve power. SInce most motion controlled outside lighting must use the same technique (works only at night). I don't want to reinvent something I'm sure is already out there. No luck finding a schematic. Thoughts ?

Franklin

Most motion controlled outside lighting is line powered and has power to the pir all the time and just does not power the relay when it is light. Not very efficient. Tell us more about your circuit, what is the pir connected to?

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- Stephen

william chan

The Parallax PIR sensor only use 100uA at 3.3v.
It is already quite power saving without a need to power down.

But if you really still want to power down, you can use any IO pin from the SX or Propeller to power the PIR sensor.
Then to power down, just change the pin to input.

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www.fd.com.my
www.mercedes.com.my

bbaumgartner

The PIR output pin will source drive an LED (2-5 ma TBD), this is part of the problem and why it needs to turn off during the day, the module must be portable. I don't plan on using a BS, et al because it adds significantly to the cost without providing any benefit that I can see. I need to make about a dozen of these units.

Thanks for your ideas, keep them coming.

Tracy Allen

Maybe something like this circuit.

The power is applied through the main transistor, and the transistor is turned on when the phototransistor is dark. The phototransistor shunts current away from the base or gate of the main transistor. A mosfet is probably the best choice for the control, because it does not require current to turn on. If you use an NPN transistor, it should be a superbeta or darlington type, so that a very small base current can control even the two or three milliamps to the sensor. With a 1Mohm resistor and a 9 volt battery, the daytime current would be 9 microamps.

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Tracy Allen
www.emesystems.com

bbaumgartner

Tracy

I had a similar thought except using a 4 log CdS photo-resistor w/NPN instead of the photoxister. I think the FET is a better choice as you indicated. B+/B- sounds like you've worked with tubes.

Barry