DC Low Voltage LIght Sensor Switch




Introduction: DC Low Voltage LIght Sensor Switch

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Need a concealed light sensor for a 12 volt circuit? Good luck finding a compact light sensor module to meet your needs in any store or online. They are few and far between to be found. Not sure why that is, but it would be awesome if a few options were on the market to purchase.

Here is a "hackish" modification to help meet your needs.

I will show how to modify an eyesore of a sensor module that you can hide inside one of your projects and better conceal the light sensor.

UPDATE: My intention was to use this sensor switch in a new project. I have come up with an alternative solution that fits my needs a little better. While this sensor would work great and might be helpful to you, please find the sensor circuit write up in my Shotgun Clock with LED and Sensor project.

Step 1: Market 12 Volt DC Light Sensor Module

Understand that this is a 12v module. The 9 volt battery is there simply to reference size. So, you will need a 12 volt source to drive this unit.

Search online for a DC light sensor and you will repeatedly come across this module. It is very common on Ebay and Amazon by different sellers.

I purchased 2 of these on Amazon for $9.99 with free shipping.

Step 2: Tools Time and Materials

Minimal tools needed for this 30 minute project.

  1. Screwdriver
  2. Mini wire cutters
  3. Mini needle nose pliers.
  4. Soldering Iron.
  5. Female to Female jumper wires.

Step 3: Tear Down

When I first received this module, the first thing I did was tear it down to see what was hidden inside the plastic enclosure.

Tear Down

  1. Remove Screw
  2. Detach Mounting Bracket
  3. Separate Blue Cap from Enclosure
  4. Pull Out Circuit Board

Step 4: Analyze Module

Wow! I was surprised to find what I did mounted to the circuit board. A big blocky and obnoxious 12v relay!


As designed, this will not meet my needs. There is no way to expose the sensor and hide the rest of the board.

Nowhere in the product description did it mention a relay control. I was hoping for a simple PCB that I could pull out and install into a project. I was hoping it would be similar to many of the PIR sensor modules on the market. No relays, just circuitry of sensor resistors, chips, and capacitors. Not this big and bulky relay.

Well, as you can see this would be very difficult to actually use and hide.

We need to make a simple modification.

Step 5: Decapitate the Sensor From Legs

What we need to due is extend the reach of that sensor so that we have more flexibility on where we can hide the circuit board and still conceal the sensor.

Note in the first picture is the LDR light sensor. We will need to eventually embed and conceal the sensor into our project and expose to light and dark while hiding the rest of the module somewhere inside the project.

You will need a small pair of cutters to cut the sensor legs about half way down. We need some legs left on the sensor and legs remaining soldered to the board. We need about a 1/4 inch on each.

After you make your cut and separate the sensor from the board look for insulation on one of the legs. Or, perhaps yours will have insulation on both. This insulation is in place to prevent shorting the circuit if the legs touch.

We need to REMOVE the insulation.

  1. I used a soldering iron and applied heat directly to the leg with insulation to soften it up a bit.
  2. Then I used a small pair of needle nose pliers to pull the insulation from the legs.
  3. Work carefully and slowly as you do not want to break the legs once cut.

Don't worry about not having the insulation as the jumper wires we install in the next steps will cover and insulation preventing shorts.

Step 6: Build Sensor Extension

If you were careful to leave about a 1/4 inch of legs on the sensor and module when you cut the sensor this next part will be easy.

Now you need your prototype jumper wires.

  1. Insert each leg for the sensor into separate wires.
  2. Connect the other end of the wire to the legs extending from the PCB.

You are ready to connect your power and load (light) and test it out.

Step 7: Connect Power

Let's connect power and get ready to test.

Remember, you need a 12v power source for this to work. Anything less will not work as the relay on the PCB needs 12 volts to open and close.


  1. Connect 12v positive to black wire on module.
  2. Connect red wire of module to positive wire of load. In our case here we have a 12v LED prewired with a resistor.
  3. Connect 12v negative to white wire on module and negative load. (light)

All connected! Ready to test.

Step 8: Test It

A note about this light sensor switch. Due to the circuitry expect about a 5 second delay for On and Off to occur.

With sensor exposed to light the LED is OFF

Conceal the LED or turn the lights off and LED is ON.

You now have a 12v DC light sensor switch ready to install in your next project. The jumper wires I used give me 6 inches to work with for locating and concealing my sensor and hiding the PCB board.

Hope this helps with your next project.

If there is anybody out there willing to fabricate a light sensor module that can be power with a 9 volt battery without a bulky relay, let me know. I am willing to purchase a well made module.

Follow me to see how I integrate this in an upcoming woodworking project. Should be pretty cool when done.

Can't Make It? Modify It!

The Water Dog

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    9 Discussions


    2 years ago

    a quick question, ive bought one of these to control the floor board lights in my car, and i have a pretty good idea on how to wire this into my circuit....buuut theirs no negative in my circuit. my light circuit is just battery>4amp fuse>switch>led strip>ground.

    if i were to wire this in after the switch would i connect to the neutral wire to ground? or just remove the neutral wire all together?


    3 years ago

    Sounds like you could have simply bought an LDR and built the rest of the circuitry for whatever you wanted it to do. LDR's are everywhere for a song. Not sure what you are using this for. IDK


    Reply 3 years ago

    Keep in mind that another purpose of this site is to help others reach their goals and explore new possibilities with their projects.


    Reply 3 years ago

    I wasn't contradicting you for how you made your project. I was merely stating that since you didn't like the huge relay assembly, there are other options to make your circuit, that's all.


    Reply 3 years ago

    No problem. You have inspired me to do exactly what you said to do. Don't Mod it... Build It! I figured out a better solution for my project. Although I think this Instructable will really help others. See my other project where I incorporated another sensor circuit. https://www.instructables.com/id/Shotgun-Shell-Light-Sensor-Clock/


    Reply 3 years ago


    Thanks for the comment and here is a simple response. Two things I am lacking to build it myself. Knowledge and materials. Believe me when I say I have tried over and over to build many of the circuits I find here and elsewhere. The first problem I run into is not having the right components to get the job done. With every new desire there comes one more piece I need to purchase. While I might have some I never seem to have all. Why, because low voltage circuitry is no my "thing". I am more of a "Jack of All Trades". I know enough to be dangerous. Now, if I do complete a circuit, then does it fit my application? That is where the knowledge comes in to adapt the circuit. I do not have that knowledge not do I have the time to learn it all. I learn as I go and have fun with all the types of projects I create. This kind of takes me to my web design and developer days. I was not an expert in any one area of design, development, sales, marketing, etc. As an sole proprietor, I had to do it all and do it well enough to be successful. And that I did, until I got burned out. So, if you would like to build me one I would would love to have something more compact where a 9 volt input would give me a 9 volt output. Let me know.


    3 years ago

    The 5" delay is to avoid false triggering. Otherwise, you'll obtain blinking lights for any shadow falling on the LDR. LDE isn't an active sensor, and isn't fast as well, but a resistor which value changes in function of the amount of light on it.


    Reply 3 years ago



    Reply 3 years ago

    LDR I meant. Light Dependent Resistor.