Introduction: DARK/LIGHT SENSOR BASED ON the LM741 Opamp

About: I'm an electronics hobbyist.I have a humongous interest in electronics.I enjoy building circuits,experimenting with ICs and MCus and fiddling and opening up any thing related to electronics or has electronic...

hey everybody,i'm going to make a dark /light sensor using a lm741 opamp .It is very easy and requires only very few parts and is quite interesting .read on.

questions for the instructables make to learn youth contest :
what did you make?
-i made a light/dark sensor based on the LM741 opamp using parts from my local electronic store.

how did you make it?
- i got the idea from a video about making a dark /light sensor using arduino,so i decided to make an easier version of it.

where did you make it?
-i made it at my school and entered it for my science fair.

what did you learn?
- i learnt how a op amp works and how to use it and all the cool circuits you can do using it.


-100k resistor x2
-4.7k resistor x1 
-photo resistor x1
-180 ohm resistor(i did'nt put a picture for this)
-lm741 opamp ic
-l.e.d(any color) x1
-jumper wires
-9v battery 
-9v battery snap and
- a breadboard

Step 2: MAKING IT!

take a look at the schemtatic and follow the steps:(use jumper wires for the following connections)
-insert the lm741 chip into the breadboard
-connect pin 4 to your negative rail of the breadboard(choose one side as your negative rail)
-connect pin 7 to the positive rail of your breadboard(choose the opposite side as your positive rail)
-connect a 100k resistor from pin 3 to negative rail of your breadboard
-connect another 100k resistor  from pin 2 to negative rail of your bread board
-connect a 4.7 k resistor from positive rail of your breadboard to pin 3
-connect the photo resistor from pin 2 to positive rail of your breadboard 
-insert the l.e.d into the breadboard (identify the positive(anode) and the cathode(negative) of the l.e.d)
-connect a 180 ohm resistor from pin 6 to positive of the l.e.d
-insert the red wire(positive) of the battery snap into your positive rail of the breadboard and the black wire(negative) to the negative rail of the breadboard.*
*note that the rails of the bread board do not run fully through the breadboard,they are split into 2 five pairs of 10 holes.


connect the battery to your battery snap and it should be working fine.move on to the next step to change it into a light sensor.If it does not work properly take a look at the schematic and make sure you have made all the right connections.

Step 4: Reversing It.

making a light sensor is very simple .all you got to do is connect the negative of the led to he 180 ohms resistor and connect  the positive to the positive rail of your breadboard and that's there is to it .if it did not work out for you email me at electronics2geek@gmail.com .Thank you and hope you liked it.i entered this for a contest  so please also vote for me.

Make-to-Learn Youth Contest

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Make-to-Learn Youth Contest

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10 Discussions


7 years ago on Introduction

I have entered the Make to learn youth contest.Please vote for me and comment on my instructable. Thank you for viewing.


4 years ago

in witch mode you use op amp


4 years ago on Introduction

yo ..i made this circuit and it works , i also presented a mini presentation (ppt) on this circuit ... thanks a lot .. you can see my ppt and work on http://techmess.page.tl


Reply 5 years ago on Introduction

may i ask? why do you have extra 2 resistor at pin 2 and 3 twisting tgt? my circuit can work but my led still light up when i close up photoresistor


7 years ago on Introduction

What contest have you entered this into? I might vote for you if I could see it.