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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...

Step 1: Things you need...

Parts:-

* 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  )

 
SyedZ66 days ago
Can I use transistor BC548
instead of TNC547 PLS reply fast
HarisC9 days ago
I made exactly same but does nt work helpppppppp
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Excuse me if I use more than one LED should I add a resistor or a transistor and can or not if use resistor 100K for R2
Dylan911 month ago

Hy i'm not an expert so maybe i made a mistake. I made the circuit you did there, but it's working in the opposite way. The LED is on in the light and off in the dark. Can Someone help what did i wrong?

GabrielK52 months ago
I don't understand something when current flows from the battery it gets to the node. Then it splits up to the 330 ohm resistor and 220 kOhm resostor. Since the first resistor has a smaller value the current must be higher there so the diode should glow at any time. Why is it turned off when the light is up?

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.

Hi please help me with this? - im a total newbie trying to learn how to dabble in the "dark arts" :-) Cant get my circuit to work and dont know whats wrong. Here are the various parts i have used.

Transistors

Bc547; Tip127; 2n3904 - could this be the problem? The tip127 is the only PNP Transistor i can see according to the data sheet...

3x Different types of Leds. Red:1.2vF White :3.2vF,

3x differnet types of light detectors

- Photo Transistor 940nm

-Photo Sensor 940nm

- LDR

Battery i am using is a 1.0ah 4.1v battery (4.1v is actual tested voltage)

2x POTS, 1x 1k, and another 10k pot.

Doing above on a breadboard

The problem is, The both LEDS stay on when connected, they just get brighter with more light, it seems my circuit is more of a light detector that switches LEDS on when it detects light rather than the opposite way around?

Ive tried switching the transistors, switching the leds, switching the POTS, and some other resistors i had (not sure of spec right now) but still cant get it right?

what other info can i add for you to assist?

Thanks, Andrew.

AndrewP143 months ago

Hi - Very detailed Instructable - im a total newbie trying to learn how to dabble in the "dark arts" :-) Cant get my circuit to work and dont know whats wrong. Here are the various parts i have used.

Transistors

Bc547; Tip127; 2n3904 - could this be the problem? The tip127 is the only PNP Transistor i can see according to the data sheet...

3x Different types of Leds. Red:1.2vF White :3.2vF,

3x differnet types of light detectors

- Photo Transistor 940nm

-Photo Sensor 940nm

- LDR

Battery i am using is a 1.0ah 4.1v battery (4.1v is actual tested voltage)

2x POTS, 1x 1k, and another 10k pot.

Doing above on a breadboard

The problem is, The both LEDS stay on when connected, they just get brighter with more light, it seems my circuit is more of a light detector that switches LEDS on when it detects light rather than the opposite way around?

Ive tried switching the transistors, switching the leds, switching the POTS, and some other resistors i had (not sure of spec right now) but still cant get it right?

what other info can i add for you to assist?

Thanks, Andrew.

kkingsbury made it!4 months ago

Followed this for a project I was working on, worked great, thanks!

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sudheerbabu5 months ago

i want the values of R1,R2,R3,.......C1,C2,C3,C4.

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sudheerbabu5 months ago
Hamow5 months ago

please i want a simple explanation for work of this circuit

SaeedH17 months ago
I have written a good article on automatic street light using 555 timer with ppt and report
http://techmess.page.tl/Automatic-Street-Light-using-555-Timer.htm
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sushaw.starry9 months ago

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

key2world11 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
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)  EastsidePrep1 year ago
yeah , it is true..
in this case should keep some distance in between LED and LDR .