How to Make a Dark Sensor

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Introduction: How to Make a Dark Sensor

About: I was 13 when I made this account so please don't make fun of my username
Hey guys ,
In this project I am going to show you how to make a dark sensor using a single transistor and some few resistors in just 3 simple steps .
here is my video this is my old dark sensor

                  

Step 1: Things You Need

Parts:-
1) 1x BC547 transistor 
2) 1x 220 k resistor
3) 1x 330 ohms resistor
4) 1- small perf board
5) 1x led (any colour )
6) wires
7) 9v battery 
8) battery clip
9)ldr(light dependent resistor )
Tools:-
1) soldering rod and wire 
2) wire stripper 

Step 2: Getting Started

solder the transistor on the perf 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 3: Finishing Touches

I have also used a SPDT switch it is optional I have used to pin headers as the connectors for the power .

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    29 Discussions

    For how much time will it glow in total?

    Making a simple touch sensor also having a finger pad. Check out this awesome Instructable.
    https://www.instructables.com/id/Making-a-Simple-Touch-Sensor-Having-a-Touchpad

    hey is there a way to make it so that when i hover my hand over it, it will stay on then when i hover over it again, it will turn off. thx

    2 replies

    I don't think so you can with just a transitor , you might need a microcontroller and PIR sensor

    A microcontroler with in combination with aLDR will do the job also

    When I supply current to the terminal the led starts glowing when there is light in the room and it still glowing after I put my hand on ldr hey please help me please!!!!!!!!!!

    Nice project.. But led is blinking fast. How can i slow it.?

    its not working the way you said

    its glowing without closing with hand any alternative for this.

    if i use 200k resistor inthe place of 220 k resistor

    and i use 300 ohms resistor in the place of 330 ohms resistor'

    thanks

    if i use 200k resistor inthe place of 220 k resistor

    and i use 300 ohms resistor in the place of 330 ohms resistor'

    thanks

    if i use 200k resistor inthe place of 220 k resistor

    and i use 300 ohms resistor in the place of 330 ohms resistor'

    thanks

    if i use 200k resistor inthe place of 220 k resistor

    and i use 300 ohms resistor in the place of 330 ohms resistor'

    thanks

    Very nice project

    but i want to use a buzzer in the place of led what should i do

    Thxx in advance

    i have a problem.
    i have followed the steps
    but instead of Dark its working as a Light Detector any idea why Thanks

    1 reply

    just change reverse the transistor because using this circuit you can make both light as well as dark sensor

    hello, nice ible!
    is there a way to control how much light there is needed to light up the led? i think it would be possible with other resistors, wich one would that be?
    I want it to light up when it is only half dark.

    1 reply

    Replace any other resistor instead of 100 k or use a 100k pot so that u can change sensivity of the sensor

    am i able to use it on 12v dc for a smd LED ??? IF SO TEll me about the things needed.