Instructables

World's best Dark / Light Sensor! (No NPN, PNP or IC!!)

World's best Dark / Light Sensor!

NO Integrated Chips!!
No NPN, PNP transistors !!

Only an LDR and a Resistor !!


 
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Step 1: Video Link

Step 2: Steps

1.Just connect any leg of LDR to any leg of LED. You can increase the light sensitivity by connecting two or more LDRs "in parallel" (like i have).

2.a) For dark detecting sensor (lights up when dark):

Choose a resistor, from 10 kilo ohms to 150 kilo ohms, in decreasing order of sensitivity to light.
Connect the resistor to the positive leg of the LED and the DC battery.
Any voltage DC battery will do. 

2.b) For light detecting sensor:

Connect the resistor to the negative of the LED and the DC battery.

Done !!

http://www.youtube.com/watch?v=dh01O22A0Xg&feature=youtu.be



Step 3: Advantages

1. Simple sensor circuit - actually no circuit at all!
2. No soldering required - relief for those allergic to it ! (like me!)
3. I have just pressed the circuit between a 9 volt battery and its cap. Even the battery cap wires were not used!!

Genius! (Idea, of course!) ;-)

Rate and vote, if you liked it!

Step 4: Dark Sensor Circuit

Picture of Dark Sensor Circuit
Here is a simple schematic circuit diagram of the dark detecting sensor circuit for led...
ClownW2 months ago

i dont get how the ldrs even effect the circuit the are beyond the led
please help me understand

pandyaketan (author)  ClownW1 month ago

LDRs behave as light switch...

they decrease resistance, when light falls on them and complete the circuit....

try it....

so just wire two ldr's to each leg of a led? thats it? well and power source

pandyaketan (author)  ClownW1 month ago

and a resistor 10 KOhm (upto 150 kilo ohm), to the positive, as per circuit in the I'ble....

cemcem19741 year ago
This is not efficent way of using energy. What you do is simply shortcircuiting the led via the ldr. When the ldr gets light it simply drops the resistance. There would be no difference therefore whether it is night or day it will consume exactly the same energy from the battery.
pandyaketan (author)  cemcem19741 year ago
1. Its not about night or day, its about light and dark, regardless of whether its day or not. 
2. LDR controls the battery energy by offering resistance, maybe you should read more.... else it would not have been used in "any circuit", not just this!
3. About 'efficiency' - if our civilization has resorted to efficiency and transparency, everything would have been free and everyone would have been happy and blissful. Most useful projects do not reach us, even though we fund them. 

"May the good belong to all the people in the world.
May the rulers go by the path of justice.
May the best of men and their source always prove to be a blessing.
May all the world rejoice in happiness.
May rain come in time and plentifulness be on Earth.
May this world be free from suffering and the noble ones be free from fears"
---- Vedic blessing

faziefazie1 year ago
Awesome tutorial, I try to make a dark sensor but I don't have IC or transistor, I just have LDR and LED, so I found your tutorial and I made a dark sensor for my room because I usually forget to turn on the light when my room getting dark in the afternoon. So I created it such a warning box for reminder me to turn on the light.

Thank you for the tutorial. Greeting from Indonesia.
PROJECT LDR res.jpg
pandyaketan (author)  faziefazie1 year ago
Wow! Even better than the real thing! ;-)

"May the good belong to all the people in the world.
May the rulers go by the path of justice.
May the best of men and their source always prove to be a blessing.
May all the world rejoice in happiness.
May rain come in time and plentifulness be on Earth.
May this world be free from suffering and the noble ones be free from fears"
---- Vedic blessing

Bill WW2 years ago
NPN, PNP, LDR?

Maybe you could provide a definition of these TLR's (Three Letter Aconyms) for the non-electronically inclined.
I've got IC figured out.

Thanks. Nice work, by the way.
pandyaketan (author)  Bill WW2 years ago
NPN and PNP are types of transistors.... wiki might help, here it is:

http://en.wikipedia.org/wiki/Bipolar_junction_transistor

LDR is Light Dependant Resistor, again search wiki ! ;-)

And thank you!

reg
ketan
----------
"May the good belong to all the people in the world.
May the rulers go by the path of justice.
May the best of men and their source always prove to be a blessing.
May all the world rejoice in happiness.
May rain come in time and plentifulness be on Earth.
May this world be free from suffering and the noble ones be free from fears"
---- Vedic blessing

what kind of ldr did you use?
pandyaketan (author)  amandaghassaei2 years ago
Typical Cadmium Sulphide one...
http://en.wikipedia.org/wiki/Photoresistor

reg
ketan