The Light Badge




Introduction: The Light Badge

About: A person who enjoys testing innovative ideas. Fan of making things blink,beep and fly.

The Light Badge is an electronic kit which utilizes an LDR( light dependent resistor) to detect lowering light levels and light a LED once it gets dark.This is a great example of an LDR in action.

This PCB can be used as a Wearable device.

Step 1: Watch Video

Step 2: Schematics:

Step 3: Theory :

When exposed to bright light,the photoresistor’s resistance is very low.It drops to around 20-30 KΩ .Current travels through the 100 KΩ resistor and then has 2 paths.It can either go through the base of the transistor or go through the photoresistor.The base of transistor to the collecor has a resistance of around 400 KΩ.Current always takes the path of least resistance.When photoresitor is exposed to bright light,its resistance is about 20-30 kΩ ,which is significantly less than the 400 kΩ of resistance the base of the transistor has .Therefore,most of the current will go through the photoresistor and very little will go to the base of the transistor.So the base of the transistor is bypassed,Thus,the transistor does not receive enough current to turn on and power on the LED.Thus the LED is off when there is lot of light in the surroundings.

When it is dark,photoresistor’s resistance becomes very high.It’s resistance goes up to 2 MΩ.This creates a very high resistance path, due to this , most of the current will go through the base of the transistor.Means that current does not go through the photoresistor when it is dark.

Step 4: PCB Design:

The board outline were made using Autodesk Fusion 360.And PCB design was done using KiCad.

Step 5: Custom PCB

Note:On the PCB I have represented anode of led with small white dotted silkscreen.

Step 6: Components Used:

  • CR2032 coin cell and Holder
  • slide Switch -11.6×4 mm
  • LED,1206 SMD package -6 (Any colour)
  • 100K Resistor
  • 1206 SMD Package
  • LDR
  • BC547 Transistor

Step 7: The Final One!

Thanks For reading

if you like this project please consider voting my entry for Wearables Contest.

All the Project files are up on Github, go make !

Happy Making !

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    Question 1 year ago on Step 2

    I build my circuit for my school but they are not going on, I dont know whwere I am goung wrong or maybe I assume its my transistor and LDR connections. Maybe you can help with the connections.


    Reply 1 year ago

    Where do you stuck ? Let me know , I am happy to help


    2 years ago

    Really handy things you created! Something that is useful for people! The best kind of creations are the ones that benefit those around us! You've created a light that doesn't need to be told to turn on and what is more is that you could make so much more with this kind of thing, you could make this circuitry as part of an outdoor light system that turns on as the sun sets, great for a basketball court or tennis court or any other application where light is needed, like on a patio for a pub or restaurant! Keep on developing your skills, and you could start to make a living out of making! All the best wishes for you my friend, never stop creating!


    Reply 2 years ago

    Thank You :)


    Question 2 years ago on Step 4

    Can I purchase this printed circuitboard? Two for practice first, then later 20 for Maker Space workshop.