Dark Sensor ( light sensor / automatic street light )

Picture of Dark Sensor ( light sensor / automatic street light )
Here is my new simple Electronics project about  Automatic Street Light Control System or Dark Sensor.

it is a simple and powerful concept , which uses transistor ( BC 547 NPN) as a switch to switch ON and OFF the street light system automatically .
It automatically switches ON lights when the sunlight goes below the visible region of our eyes. ( e.g in evening after Sunset ).

it automatically switches OFF lights when Sunlight fall on it ( e.g in morning ) , by using a sensor called LDR (Light Dependent Resistor) which senses the light just like our eyes.

Needs no manual operation for switching ON and OFF...
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Step 1: Things you need...


* 1    BC547 transistor
* 1   220 k resistor
* 1   330 ohms resistor
* 1   LED (any colour )
* 1   9v battery
* 1   battery clip
* 1   LDR ( light dependent resistor  )

Step 2: AND...

Picture of AND...
*  Connecting wires
*  soldering rod and wire
*  wire stripper
*   Cutter

Step 3: Circuit diagram

Picture of Circuit diagram
solder the transistor on the board and solder one wire of the LDR to the emitter and other to the base  , solder the negative wire of the LED to the base of the transistor with a 330 ohms resistor and also solder 220k resistor with the one side of the 330 ohms resistor .

Step 4: Finsih... Uuuhuuuu... :p

Picture of finsih...   Uuuhuuuu...  :p
The simple circuit is ready for testing now . Connect 9v battery terminals to the circuit as show in fig and see the output . As you block light falling on Light dependent resistor (LDR), the LED glows .

What procedure has been followed to choose the above specified values of the resistors and transistor?

key2world2 months ago

what should i do to replace the led with a cfl?

Ive made something light this (use more components) in a small robot I made (as seen in the profile picture) And I was going to update it to this smaller version but I wanted to check if copying you design was okay
BurgersBytes10 months ago

The circuit can run 2 LED's for over a month with just 2 AA batteries. I use a similar one to light up my wall clock with 2 bright warm white flat top LED's.

EastsidePrep11 months ago
How do you make sure that when the light turns itself on, it doesn't then sense the light and turn itself back off?
Er Varun Goyal (author)  EastsidePrep10 months ago
yeah , it is true..
in this case should keep some distance in between LED and LDR .