LDR DARKNESS SENSOR – LED OFF AS LIGHT FALLS

We will discuss LDR darkness sensor – LED OFF as light falls on LDR and Turn ON in the dark here, it has a previous part which is LED ON as Light falls on LDR and Turn OFF in the Dark

REQUIRED HARDWARE 

S.No. Item Quantity
1 LDR 1
2 Resistor 1K 3
3 Resistor 220 1
4 LED 1
5 OP-AMP LM358 1
6 Battery 5V / 9V 1
7 Male to Male jumper 8

LDR DARKNESS SENSOR – LED OFF AS LIGHT FALLS

WORKING

As we can see the output of the bridge is fed into an op-amp. The output of terminal A fed to inverting (-) input of op-amp and output of terminal B fed to non-inverting (+) input of the op-amp.

We know as light falls on LDR its resistance starts decreasing corresponding to the intensity of light and in the dark resistance increases, we know current will follow the low resistive path. So, if light falls on LDR it has low resistance means more current will pass through LDR (more at point A) while in the dark more current will flow through another path (at point B).

So in sunrise point A has more current and B has less. In dark B has more current and A has less.

We know op-amp compares inverting (-) and non-inverting (+) voltages and passes which one is greater. So

IN LIGHT

  • Voltage at inverting (-) is Higher. We know if a signal is fed into inverting (-) of op-amp it does change the polarity of the signal. So the output of the op-amp is negative
  • Voltage at non-inverting (+) is Lower.

That implies LED will get this negative voltage and remains OFF as it is reversed biased.

IN DARK

  • Voltage at inverting (-) is Lower.
  • Voltage at non-inverting (+) is Higher. We know if a signal is fed into non-inverting (+) of the op-amp it does not change the polarity of the signal so the output of the op-amp is a positive voltage.

That implies LED will get this positive voltage and would turn ON as it is forward biased.

 OUTPUT

As light falls on the LDR output of the op-amp is negative voltage means LED gets the negative signal that makes LED to be turned OFF and in the dark output of the op-amp is positive LED will get the positive signal that needed by LED to be turned ON.


READ NEXT
IR SENSOR AND ARDUINO


 

0 0 votes
Article Rating
Subscribe
Notify of
guest
62 Comments
Most Voted
Newest Oldest
Inline Feedbacks
View all comments
buy watch
buy watch
1 year ago

696888 293838Attractive part of content material. I just stumbled upon your website and in accession capital to claim that I acquire in fact enjoyed account your blog posts. Any way Ill be subscribing to your feeds and even I achievement you get entry to constantly speedily. 262053

Amelia
Amelia
1 year ago

591665 176412I just added this webpage to my feed reader, fantastic stuff. Cannot get enough! 227228

design your own vehicle graphics
design your own vehicle graphics
1 year ago

299573 184486Its like you read my mind! You appear to know so much about this, like you wrote the book in it or something. I believe which you can do with some pics to drive the message home a bit, but instead of that, this really is amazing blog. A fantastic read. Ill surely be back. 481042

tailgate mural
tailgate mural
1 year ago

848743 678793Its onerous to search out knowledgeable individuals on this subject, even so you sound like you already know what you are talking about! Thanks 761240

đăng ký fun88
đăng ký fun88
1 year ago

952738 380298As I internet website possessor I believe the content matter here is rattling amazing , appreciate it for your efforts. You should maintain it up forever! Excellent Luck. 311677

poker 99
poker 99
1 year ago

109016 472403This will be a terrific blog, might you be involved in doing an interview regarding just how you designed it? If so e-mail me! 397537

www.1poker99.com
www.1poker99.com
1 year ago

449925 242438Flexibility indicates your space ought to get incremented with the improve in number of weblog users. 722178

طراحی سایت
طراحی سایت
1 year ago

131489 332305Some really marvellous function on behalf with the owner of this internet website , perfectly excellent content material . 710378

Gold Silver and Stock Market Economy in 2020
Gold Silver and Stock Market Economy in 2020
1 year ago

105696 852665Currently it seems like BlogEngine is the very best blogging platform out there right now. (from what Ive read) Is that what you are using on your blog? 283658

rajaqq
rajaqq
1 year ago

556102 494393Exceptional weblog here! following reading, i decide to buy a sleeping bag ASAP 603302

62
0
Would love your thoughts, please comment.x
()
x