Automatic Night Light

[Electroenthusiast]

I want to design a automatic night system using a photocell,
that switches ON the Florescent Bulb, when Natural Light is Dim.
Can anyone give me an Idea?
I dont want to use relay this time. But will use if there's no other go.

 

[Sceadwian]

This is a typical case of why build it when you can buy it?

 

[Electroenthusiast]

This is a typical case of why build it when you can buy it?

still i want to build it...
at least i want to know how i can do it.

 

[AllVol]

Once you get it turned on, how will you turn it off?

 

[HarveyH42]

I want to design a automatic night system using a photocell,
that switches ON the Florescent Bulb, when Natural Light is Dim.
Can anyone give me an Idea?
I dont want to use relay this time. But will use if there's no other go.

Haven't gotten around to it yet, but have a need for 6V switch for a battery powered fluorescent light. You didn't specify if yours was battery or mains (outlet) powered. If you plug it in the wall, there are very inexpensive/safe units on the market. Should have looked for after Christmas specials. Saw some without a timer for $4, and a 6' cord. For battery powered like mine (4xAA), tough to know what you need, if you don't state more clearly what you want. Tubes come in many sizes, wattage.

 

[Mikebits]

Maybe you can find something here.
night light circuit - Google Search

 

[BrownOut]

Maybe you can find something here.
night light circuit - Google Search

I think this one gets you started: Night Ligit Circuit. Replace R1 and the LED's with an appropriately sized relay that operates your flourescent light, and you're there.

PS: A comparator between the sensor and transistor with hysterisys would prevent the relay from chattering as the ambient light dims.

 

[Electroenthusiast]

I think this one gets you started: Night Ligit Circuit.......

Can you please Explain me the working of the Design?
Looks Simple, a Voltage-Divider Transistor Circuit... Am i right? can i design using it?
Does Photcell exhibit Resistance? When Exactly Does LED glow?
How can i vary the sensitivity of Photcell (i.e.,work for various light intensities)?

 

[BrownOut]

Check this out: Light Dependent Resistors

 

[jakeselectronics]

This is a typical case of why build it when you can buy it?

where's the fun in that!

I just built one.
cost me 7 bucks.
Found everything execpt the enclosure in the shed.
even used IEC connections off an old computer power supply, and a 8A 250VAC spade lug relay out of an old microwave.

Im hoping to change it over to A/D rather than transistor threshold type of thing.

Here's a pic or 3:

 

[Electroenthusiast]

Check this out: Light Dependent Resistors

Thank You very much...
since i'm a learning student i have some ques
can i use a Potentiometer (for Preset Resistor), two Npn SL-100 Transistors(Why not one?), and a Relay instead of LED(Do i require another Transisor for this)?

 

[BrownOut]

Potentionmeter - Yes
NPN - Two requrires less current from the photo detector. One would probably work
Relay would probably work. No series resistor required

 

[Electroenthusiast]

Thanks...
will design it/ timed circuit...

 

[BrownOut]

where's the fun in that!

I just built one.
cost me 7 bucks.
Found everything execpt the enclosure in the shed.
even used IEC connections off an old computer power supply, and a 8A 250VAC spade lug relay out of an old microwave.

Im hoping to change it over to A/D rather than transistor threshold type of thing.

Here's a pic or 3:

That's awesome! There's one big reason to build your own, even when commercial units are available... Nerdvana!

 

[Electroenthusiast]

i have some doubts in the design?
Where should i put the R1,R2,RE,RC?
R1> ???
R2> in series with presettable resistor?
RE > in series with LED and another;
RC > not there in the circuit-diagram? Why Cant i use it?
Shouldn't i use actual resistors and then use additional presetable resistors?

Answer Please I'm Still Learning

 

[AllVol]

Answer Please I'm Still Learning

First, be aware that the circuit you show after Ryan, is a light detector. It will react in the presence of light and its LED will then glow. However; it is a simple matter to change. Merely swap the locations of the LDR and preset resistor.

Now, to your questions:

R1 is the LDR
R2 is the preset resistor, a potentiometer. If you don't have one, measure the resistance across the LDR when dark, and try to find a resistor close to that reading. That will give you an equal voltage divider, and a good start.
RC is the current limiting resistor that goes with every LED
You don't need an RE because this is a switching circuit, not an amplifier or emitter follower.

The two transistors form a Darlington pair - more bang for the buck, but not really necessary. One small signal NPN will do.

Make the changes I have recommended, build the circuit as closely as you can, and you will have a circuit that will turn on a LED when the ambiant light (roomlight) is dark enough. It will not turn on your tube light... that requires much more circuitry. But it is part of the learning process.

 

[Electroenthusiast]

i did the circuit, using transistor SL-100;
i couldn't make the LED glow at the required darkness,
the light keeps glowing till a bright light is subjected to it.
Is it because the LDR i'm using? Should i use a different one?
i'm using a 10K Potentiomenter for the circuit?
Why is it not working? What changes should i make?

 

[AllVol]

Why is it not working? What changes should i make?

Not being able to see your circuit makes troubleshooting difficult.

I think all we have is a matter of calibration. Adjust the pot through its range and you should find a point where the LED will go off in rather dim light. Using that point as our trigger point, we should find that any darker conditions will cause the LED to glow, but stay off if more light is applied.

If adjusting the pot through its range has no noticable effect, swap the positions of the LDR and pot and try again.

 

[swagatam]

Circuit diagram of a simple and precise automatic night light: **broken link removed**

 

[AlainB]

This design found in the web is working very nicely:

**broken link removed**

The breadboard circuit is for counting something that is breaking the light beam to the photocell but the principle is the same. The 10K VR will fine tune the intensity of the light needed to trigger the relay.

Alain