Surprise Secret Of This PIR Sensor

Well.. Well... Well ... what do we have here?

This is a wildly popular Passive Infra Red sensor (PIR).
It has a hidden secret up it's sleeve and I want to show you what it is!


PIR Sensor With Freznel Lense


But first, how it works!

It uses a Fresnel lens which sits in front of a heat based sensor to detect objects about 7 feet away.

It also has the ability to delay firing by 2-4 seconds approximately. Great for filtering out unwanted movements from retriggering the sensor.

BUT! It has another trick up it's sleeve.

Ready, Ready?

These sensors normally trigger when it see's any type of motion, doesn't matter if the lights are on or off, it will trigger.

But what if you want to build something where you only want to trigger when the lights are off?

Something like this under bed lighting system perfect for those midnight runs to the loo. It will only go on when it sees motion in the dark!


Fun side story...

I almost bought this exact model myself, but I wanted to add another sensor for my dog...

Yeah, long story here but he can't see the pet stairs and needs his own light. 

So I have one for my girlfriend, myself and my pup of course, I can control all the colors!

Ok, back to this little sensors super power!

In order to make this sensor only trigger when its dark, all you have to do is add a simple electric eye to the circuit itself.

Photo Resistor

Ps- electric eye is an old term... they are also known as Light Dependent Resistors.

Best part? It's pre-configured for this, so just pick up an electric eye like the one you see above and solder it in.

All you need to do is pop off the lens, and look for the 2 pins directly under the heat sensor.

See picture below for location.

Pretty awesome right?

So if you're interested in building your own awesome electronic projects I'd like to invite you to check out our Dr.Duino Explorer PLUS and Dr.Duino Pioneer PLUS.



Be sure to check out our other blog articles especially:

What can you do with Arduino?

What's better, Arduino Or Raspberry Pi?

So What Is Arduino Exactly?