Jeanie

I have set up a simple LDR ciruit with LDR, LED; 1K resistor and 12K resistor in series and a transistor E to battery, C to LED and base to 1 resistor and when LDr exposed to ligh LED is on. When exposed to dark LED goes off

HEEEEEEEEEEELLLLLLLLLLLLLLLPPPPPPPPP

Hero999

http://www.techitoutuk.com/knowledge...amp/index.html

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ericgibbs

Can you post a sketch of the circuit, so we can see how its connected.

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Eric
"Good enough is Perfect"

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audioguru

Hi Jeanie,
If you attach a sketch of your circuit for us to see how it is connected then we will see what you are talking about.

Hi Hero,
Your diode D3 is backwards. EDIT: It isn't backwards.
Your "transistor" has 5 legs??

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Uncle $crooge

Hero999

A comparator is a much better way of doing it, for even better results connect a 470k resistor between pin 6 and pin 3.

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audioguru

Hi Alun,
OOps, Hi Hero,
Of course a comparator is the best way to turn an LED on and off with light.
But a single transistor would probably fade the light on and off slowly.

Now that the daylight hours are getting less and less each day, I am souping up my solar garden lights. I have 5 different circuits and the best one uses a single AA Ni-Cad battery cell, a voltage stepup circuit with an inductor and a fading red, green and blue LED.
2 circuits use an LDR to detect darkness. The others use the reduced output from the solar panel. The solar panel detector is the best and uses fewer parts.

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bananasiong

Hi,
Can I know what does D3 do in the schematic posted by Hero?

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Hero999

Reverse polarit protection, it's totally optional and can be placed on the + rail which will make no difference.

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I also post at the following sites:
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Screen name: Aloone_Jonez

Jeanie

Hero,

I want some 15 year olds to set up a circuit using a 1K resistor, a 12 K resistor, a transistor, an LED and LDR. When exposed to dark the LED should light I did it once before so why is it working the opposite way now.Can you give a diagnosis.
They dont believe me now!!

Nigel Goodwin

As you've already been told, post the circuit as you have it connected already.

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audioguru

Hi Jeanie,
Why didn't you attach the schematic of your very simple circuit and explain that before the LED lighted (lit?) when it is dark but now the LED lights when it is light????????
Hmmmm???

Hint: Maybe before the LDR turned on the transistor when the LDR got dark.
Guess what the LDR is doing now???

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Uncle $crooge

Jeanie

Tried to copy and paste my circuit diagram it just will not paste I dont want to add my lack of computer knowledge as well. Apparently i read the circuit wrong. i let out a variable resistor. I will try again tommorow and report to you guys thanks for all the replies and all the telling offs!

ericgibbs

hi,
One way to post a drawing.

Open the 'Post Reply' window.
Look down the screen, 'Additional Options'
A button named 'Manage Attachments', left click it
A new small Window should appear.
Click the 'Browse' button, then find your drawing within your PC.
Then click the 'Upload' button,,,, wait until its done uploading.
Then click 'close window' message

Make sure that your drawing or whatever is on the list of acceptable file extensions and also the size limit.

Give it a go!, we are all waiting to see the circuit.

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Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/