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Postby Tuneking » Fri Apr 22, 2016 10:19 am

I'm using 4.5 volt to illuminate 2 diodes (in parallel) that each require 4.5 volts. Simple.
Now I want to insert a sc-hr501 Pir between the battery and diodes to be a motion sensor. I hoped that the Pir would simply act as a switch and pass the battery's 4.5 volts on to illuminate the diodes ... But too little voltage is being output by the Pir. Am I doing something wrong? It has been suggested that I need to add a transistor to redirect the battery's 4.5 volts directly to the diodes when the Pir becomes active. Can you help? Thank you.
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Re: Pir

Postby awright » Sun Jan 07, 2018 2:03 am

At a quick glance I did not see an output current rating for the sc-hr501 in their info sheet, but it appears that your pair of LEDs is demanding more than the PIR circuit can supply. A simple single NPN transistor circuit should overcome the PIR output current limitation. Emitter to negative rail. Collector to cathodes of the LED pair. LED anodes to positive rail. Base driven from PIR output with a series resistor to limit base current to, say, twice that required to fully turn on LEDs. I am assuming that you want the LEDs illuminated when the PIR output goes high. If you want to illuminate the LEDs when the PIR output goes low, use a PNP transistor, emitter to positive rail, collector to anodes of the LEDs, and LED cathodes to negative rail.
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Re: Pir

Postby KMoffett » Tue Jan 23, 2018 1:06 am


That thread was last replied to almost two years ago. You are creating a zombie. ;)

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