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Light intensity detector

Gryd3

Jun 25, 2014
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Have you built or experimented with the circuit I had provided, or have you looked into how the drawing you found works?
You will need to jump on something to have it work. You can use the first circuit with a 9V battery, but will need to swap out R4 for a 330Ω resistor.

You should really get some parts and try to get something to work.
You had said on Sunday this needs to be done in 1-2 days, we're on day 3, and now you can submit it on day 4? I am a little unsure how you want me to proceed.
 

ayush soni

Aug 24, 2014
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i asked for some more time
bcoz the project is complicated & advance for kid of my age :p but the day after tomorrow is the final date after that they will not take my project


& i am sending u a message to make sure about everything
 

Gryd3

Jun 25, 2014
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& i am sending u a message to make sure about everything
again, please keep it in the thread. It keeps all the info in one spot and will help any others working on a similar project.
 

ayush soni

Aug 24, 2014
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lol
i am feeling like a dump person while asking those stupid questions that y i sent u a message :p
i am new in field of electronics & its my first project :D
dont want to mess it & also m in under a lot of pressure of expectation :p
& i only have tomorrow its already 12:24 in my country :'(
 

Gryd3

Jun 25, 2014
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lol
i am feeling like a dump person while asking those stupid questions that y i sent u a message :p
i am new in field of electronics & its my first project :D
dont want to mess it & also m in under a lot of pressure of expectation :p
& i only have tomorrow its already 12:24 in my country :'(
It still helps everyone reading it, and no one on here knows you, so you don't have to worry about anyone talking to you in real life about it.
Because of the price of the parts, it may not hurt you to go buy the parts for both circuits.
The one I posted, and the one you did. Resistors are pennies, and so are transistors.
Don't stress over finding a specific transistor part number, a generic one will do as long as it's NPN type.
 

ayush soni

Aug 24, 2014
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ok thxx dude
will you please post a final list of things i will i have to buy for both circuits ?
m still little confused :p but i think i will not fully understand all this thing unless i try the circuit on breadboard :p
 

Gryd3

Jun 25, 2014
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i think i will not fully understand all this thing unless i try the circuit on breadboard :p
Exactly!
This is a project you should be able to build and understand.
Do you have a multi-meter? (Very very handy... pretty much a requirement, but this project can be done blind)
Get yourself at least 5 or six NPN transistor.
Get an assortment of resistors from 100Ω - 1kΩ at least 2-3 of each value. (Spares in case one gets burned!... You can always connect two 500Ω resistors together to make a 1kΩ)
Get a couple LDRs, again. In case one breaks.

That should be good to get you going, and provide enough parts to adjust and experiment.
 

Gryd3

Jun 25, 2014
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Once you get the parts, draw out the circuit yourself.
Then you can build it. Double check your connections, and you can supply a clear picture of the built circuit, and drawing, and someone can double check. Or you can hook up the battery and see. The parts are cheap, so if something pops, you can find out why, or ask why.

My project in school was a line-following robot, there were many more parts and I needed to etch my own board. These things are only complicated if you rush into it. If you take the time to learn how each little part works, you will understand the bigger circuits.

(Reading out a transistor works, and how to use Ohms law will be a huge asset for you)
 

ayush soni

Aug 24, 2014
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ok thxx dude
& sorry m feeling very sleepy
its midnight here :p & m very tired
& the first think tomorrow i will do is to try those circuits & see if they work properly or not
& if get any problem i will post it here
thxx again
& byee
good night guys :D
 

Gryd3

Jun 25, 2014
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ok thxx dude
& sorry m feeling very sleepy
its midnight here :p & m very tired
& the first think tomorrow i will do is to try those circuits & see if they work properly or not
& if get any problem i will post it here
thxx again
& byee
good night guys :D
With both circuit!
Remember that the LDR and a resistor are connected to make something called a voltage divider. Look at R2 on my drawing and R4 on yours. You can swap that one for different values to change how light the room must be for your LED to switch on/off. This is where the actual switching happens... As the LDR is moved from light to dark, the resistance changes, which changes the voltage that is present on the transistor.

The resistor connected to the LED MUST be sized for the battery you use. If too small a value is chosen, you will burn out the LED. If it is too large, the LED will simply not be as bright.

Post if you run into problems. and Experiment! it will help a great deal if you play to understand how the parts work.
 

ayush soni

Aug 24, 2014
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Finally its done & working fine
thxx to all of you & specially thxx to Gryd3 thxx dude :D




information for everyone else who also want to make it
Components i used
2 resistors ,1 transistor , 1 led ,LDR & a bread board

i am using one resistor of 330Ω & another of 100kΩ
transistor is BC547
& i think u can take any LED & one LDR

& here are some question i want to ask


the resistance value of LDR increase in dark & decrease in light how ?
& in this circuit when i increase intensity of light then resistance value should decrease & current should easily flow but its not happening
& thats transistor work here ?

plz explain working of transistor & LDR in this circuit in detail
i will also do some research on google
 

Gryd3

Jun 25, 2014
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Finally its done & working fine
...
& in this circuit when i increase intensity of light then resistance value should decrease & current should easily flow but its not happening

Just to clarify, you had built the circuit from your picture, and not mine. Correct?

Can you please clarify what is not working? You said it's working fine, but then something is not happening. Explain further and I can help out.
 

ayush soni

Aug 24, 2014
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the circuit is working fine

here is a very short video if u want to see

& my questions are

the resistance value of LDR increase in dark & decrease in light how ?????
& in this circuit when i increase intensity of light then resistance value of LDR should decrease & current should easily flow but instead of this led is turning of y ? i mean why led is turning of when intensity is increasing ? the value of resister value is decreasing so who is turning of let ?? is that because of transistor ?

& plz explain working of transistor & LDR in this circuit in detail


PS i gave it name "Photo Eye" :p
do u like it ?? :p
 

ayush soni

Aug 24, 2014
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if u still didnt get the question

i want to ask if increasing light will decrease resistance value of LDR why led is turning of ? who is responsible for that ? & what actually happening ??
 

Gryd3

Jun 25, 2014
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the resistance value of LDR increase in dark & decrease in light how ?????
& in this circuit when i increase intensity of light then resistance value of LDR should decrease & current should easily flow but instead of this led is turning of y ? i mean why led is turning of when intensity is increasing ? the value of resister value is decreasing so who is turning of let ?? is that because of transistor ?

& plz explain working of transistor & LDR in this circuit in detail


PS i gave it name "Photo Eye" :p
do u like it ?? :p

Here is an article of how an LDR works from Wikipedia. Its a little bit of jumbo, but the light provides a little extra energy to allow the electrons to flow easier through the LDR.

R4 and the LDR for something called a voltage divider.
What happens is when the LDR is in the light, it's resistance drops. This also decreases the voltage in-between the LDR and R4. This voltage is what is being provided to the 'Base' pin of the transistor. So when you shine light on the LDR, the voltage being provided to the 'Base' of the transistor drops. When the voltage drops low enough the transistor turns off, cutting power to the LED.
When the LDR is in the dark, it's resistance goes back up. This also increases the voltage in-between the LDR and R4 which is fed to the transistor which forces it to turn on.
Please note that this will ONLY work with more than one resistor. (The LDR is a type of resistor)

Does that help?
 

ayush soni

Aug 24, 2014
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yup its helpful thxx

so in this circuit when i flash on it the resistance value of LRd decrease & voltage difference also decrease which cause LED to turn of
i am right ??

& what transistor work here ? & y its pins are names as C,B,E ?? what's their full form ?
 

Gryd3

Jun 25, 2014
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yup its helpful thxx

so in this circuit when i flash on it the resistance value of LRd decrease & voltage difference also decrease which cause LED to turn of
i am right ??
Yes you are right. but ONLY because of how it is connected to R4. R4 is on the + side, and the LDR is on the - side.
If you swapped R4, and R1(LDR) the voltage would INCREASE as the resistance of the LDR decreases. (Experimentation for later)
If you have a multimeter / voltmeter you can measure the 'Base' of the transistor and watch the voltage change as you shine the flashlight on it.
& what transistor work here ? & y its pins are names as C,B,E ?? what's their full form ?
Collector, Base, Emitter.

When the voltage increases to the Base of the transistor, current begins to flow into it which will turn it on. Transistors are funny creatures though and can actually be part-way between on and off. How you are using it is on or off.. no where in between, but you may accidentally turn it halfway on if you gradually change the light. This is not recommended if you power something that is power hungry because the transistor can get hot when turns on half-way.
 

ayush soni

Aug 24, 2014
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Dude this the the new circuit digram i used (in attachment)
& i didnt found any 6V batter so m using a 9V battery

& i found this video

& i got it what is happening with LDR
bu still confused about transistor :p

can u show me flow of current with digram ?
in dark & bright both the case ?
what m not getting is flow of current
 

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Gryd3

Jun 25, 2014
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The line along the top of that diagram is all 6V (Or 9, because of your battery choice)
The line along the bottom is 0V.
Point B will be somewhere in between anywhere from 1.5V to almost 0V.

If you ignore the transistor for a second. and focus on the LDR and R2. The voltage where they join is part-way in between the voltage at the top and the voltage at the bottom. 6V and 0V in the drawing. You can determine the voltage at point B with the following:
Vb = Vtotal / (R2 + LDR) * LDR

When the voltage at point B is high enough, the flow of current through the transistor reaches a point where it will switch on and allow current from the LED to flow through it.
 

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ayush soni

Aug 24, 2014
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ok got it :D

thxx
& last question
if the case of light y the maximum amount of current will from from R2 then LDR ? & less current will flow to LED ?

according to me bcoz of more potential difference of R2 (100k Ω) & LDR (with maybe 1kΩ or something like that)

am i right ??

potential difference between R2 & LDR is high in bright room to maximum current will flow through it
right ?
& m little scared about presentation anything u can suggest me or i should know before giving presentation ?
& if u know any more question which can be asked plz also give me their answers :p
 
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