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

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

Only an LDR and a Resistor !!


Step 1: Video Link

 
faziefazie2 years 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

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.

pandyaketan (author)  AndrewP143 months ago

Probably, interchanging the Emitter and Collector connections of your pnp should do it.

Search for "Dark Detector" (Solar) circuit, here or on google and compare your diagram....

hope it helps, since you have not provided a link to your circuit...

Hi Pandyaketan - Thank you so much for your response - i was going nuts trying to figure it out after over 10-12 hours of tampering, changing etc. Turns out it was the resistance value leading to the (Base) of the transisor - the resistance was not high enough, i used a 300k resistor from (+) to Base on one side, Photo-transistor on the other side of Base (transistor in the middle of the board -using breadboard).

See below image - i used a different schematic.

Again, Thank you for your assistance.

20150526_221340.jpg
pandyaketan (author)  faziefazie2 years 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

AndrewP143 months ago

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.

ClownW11 months ago

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

pandyaketan (author)  ClownW10 months ago

LDRs behave as light switch...

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

try it....

ClownW pandyaketan10 months ago

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

pandyaketan (author)  ClownW10 months 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

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