Surprise Secret Of This PIR Sensor

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


PIR Sensor With Freznel Lense


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 like these

Photo ResistorPs- 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 this one, and solder it in.

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

See picture below for location.

If you want to get your hands on a few of these, you can get them right here from Amazon.

 Cool right?

I thought so too!

Happy Sensor-ing...!!

Let me know what you think by commenting on this post!


PS- If you thought this was cool, checkout my biggest Arduino build ever featured by Apple, hackaday, make magazine and so many more. Its called Gooniebox.




  • Wow what a clever little sensor now I really do wish I win the kit!

    Glenn Wellstead
  • @Joseph Matus The link I posted for the LDR has a bunch of them inside of one kit. I don’t recall which one i used exactly. I just kept trying each one in the kit till i found one that worked for my room.

  • What value “Light Dependent Resistor” did you end up using?

    Joseph Matus
  • Dig it.

    Justin Lowe
  • I played with Arduino about 9 years ago. I could see the almost limitless potential but never got far. I decided to get back into it, stumbled on you and I’m on my way! Now when I build this PIR triggered night light I won’t need to worry about tripping over you in the dark!

    Seriously, I like what you do. Please keep doing it!

    Dave Dembinski

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