is there a way to increase the light of an LED with a dial?

[Victory]

I am trying to work out a way to increase the light intensity with a
dial for a regular LED from a dollar store flashlight. I don't know
much about the LED since I can't see any markings.
What would I need to buy from Radio Shack or an electronic store to do
this?

Thanks

 

[Michael Kennedy]

I am trying to work out a way to increase the light intensity with a
dial for a regular LED from a dollar store flashlight. I don't know
much about the LED since I can't see any markings.
What would I need to buy from Radio Shack or an electronic store to do
this?

Thanks

You probably cannot increase it. Do you mean decrease the light? You could
use a varible resistor to adjust the output to the LED.

Mike

 

[Victory]

I guess I am looking for a dimmer or something for it - just a dial
that can turn the light up to full or down a little depending on what
I want. But I want it to be controllable with a dial or something. I
hope that is clearer.
Thanks for the quick response and looking forward to the next one!

 

[Smitty Two]

I am trying to work out a way to increase the light intensity with a
dial for a regular LED from a dollar store flashlight. I don't know
much about the LED since I can't see any markings.
What would I need to buy from Radio Shack or an electronic store to do
this?

Thanks

A book on fundamental electronics.

 

[James Sweet]

I guess I am looking for a dimmer or something for it - just a dial
that can turn the light up to full or down a little depending on what
I want. But I want it to be controllable with a dial or something. I
hope that is clearer.
Thanks for the quick response and looking forward to the next one!

You want a variable resistor. The value depends on the particular LED but
you might try 2.5K or 5K.

 

[Michael Kennedy]

You want a variable resistor. The value depends on the particular LED but
you might try 2.5K or 5K.

Yes, James ie right. You don't want a varible resistor like I said. You want
a variable resistor. haha. I'm terrible at typing.

Mike

 

[Arfa Daily]

Yes, James ie right. You don't want a varible resistor like I said. You
want a variable resistor. haha. I'm terrible at typing.

Mike

It may not work with a simple variable resistor because at higher settings,
the current will increase enough to probably just burn out the small piece
of the pot track that's still in circuit. A fixed resistor will also still
be needed to limit the full brightness current. In order to get a decent
control range, without risk of over-running the pot's track and wiper, I
would suggest that a small transistor needs throwing into the mix to control
the LED current, whilst the pot is left the low-current job of controlling
the transistor's base. If I get time today, I'll give it a try.

Arfa

 

[Dave Plowman (News)]

I am trying to work out a way to increase the light intensity with a
dial for a regular LED from a dollar store flashlight. I don't know
much about the LED since I can't see any markings.
What would I need to buy from Radio Shack or an electronic store to do
this?

Google on LED driver. That should keep you occupied for some time. ;-)

If you wish to increase the brightness beyond that a constant current
driver can do you'll be into a pulse circuit.

 

[Arfa Daily]

It may not work with a simple variable resistor because at higher
settings, the current will increase enough to probably just burn out the
small piece of the pot track that's still in circuit. A fixed resistor
will also still be needed to limit the full brightness current. In order
to get a decent control range, without risk of over-running the pot's
track and wiper, I would suggest that a small transistor needs throwing
into the mix to control the LED current, whilst the pot is left the
low-current job of controlling the transistor's base. If I get time today,
I'll give it a try.

Arfa

OK. I just tried it with a few bits that came to hand. White LED. 200k pot.
82k resistor. 2N3904 transistor. 12v supply. LED current adjustable from 0 -
25mA. You could also do it using an adjustable regulator as a constant
current source.

Arfa

 

[Victory]

Thanks for your help. Great to hear it worked. I don't want to go
above the brightness limit of the LED, so that shouldn't be a
problem,.
Now all of the parts you just listed, are they some of the things I
can find at a local Electronic store, Radio shack or something I need
to find online? Also, what kind of cost am I looking at here?

 

[GregS]

I am trying to work out a way to increase the light intensity with a
dial for a regular LED from a dollar store flashlight. I don't know
much about the LED since I can't see any markings.
What would I need to buy from Radio Shack or an electronic store to do
this?

Thanks

You could buy one of the dollar stores lanterns with a variable output, and transfer the ckt.
Its not going to fit inside the flashlight, but you might be able to size down the ckt.

greg

 

[Arfa Daily]

Thanks for your help. Great to hear it worked. I don't want to go
above the brightness limit of the LED, so that shouldn't be a
problem,.
Now all of the parts you just listed, are they some of the things I
can find at a local Electronic store, Radio shack or something I need
to find online? Also, what kind of cost am I looking at here?

Parts values are not that critical. Any linear taper pot of around that
value (150k, 200k, 220k, 470k), any resistor around that value (68k, 82k,
100k, 120k, 150k). Might be worth you getting a few resistors of around that
sort of value, and just experimenting to see which one gives you best
adjustment range with the pot value that you finish up using. The value of
this resistor, along with the gain of the transistor, will determine the
full on current through the LED. Start with the highest value resistor, and
the pot turned right down to the ground end, and measure the current through
the LED as you slowly turn up the pot. You don't really want more than 25mA
through a standard white LED. The brightness did not increase much above
about 18mA, with the example I tried. As far as the transistor goes, any
general purpose NPN small-signal silicon transistor with a collector rating
of 100mA or so, will be fine, so 2N3704 or whatever you can lay hands on.
Any electronics component store should have these parts on the shelf. Prices
are cents.

In case you don't know how I hooked this up, it was fixed resistor top end
to +12v, bottom end to the clockwise (from the front) tag on the pot.
Anticlock tag of the pot to ground (supply "-") together with transistor
emitter. Transistor base to centre tag of pot. LED anode to +12v. LED
cathode to transistor collector. Measure current in LED by inserting
milliammeter in series with LED ( meter "+" to +12v, meter "-" to LED anode.

Arfa

 

[James Sweet]

It may not work with a simple variable resistor because at higher
settings, the current will increase enough to probably just burn out the
small piece of the pot track that's still in circuit. A fixed resistor
will also still be needed to limit the full brightness current. In order
to get a decent control range, without risk of over-running the pot's
track and wiper, I would suggest that a small transistor needs throwing
into the mix to control the LED current, whilst the pot is left the
low-current job of controlling the transistor's base. If I get time today,
I'll give it a try.

Arfa

Well I was assuming the original resistor was still in place, but yeah you
do need it.

 

[GregS]

Thanks for your help. Great to hear it worked. I don't want to go
above the brightness limit of the LED, so that shouldn't be a
problem,.
Now all of the parts you just listed, are they some of the things I
can find at a local Electronic store, Radio shack or something I need
to find online? Also, what kind of cost am I looking at here?

Well RS used to have stuff like that. Since they shut down my RS
I don't get there much anymore.

I still didn't hear a full purpose of this. The good dimmers use pulses to
control brightness, much more efficient. The switched dimmer as seen
on the $10 lanterns at the dollar store and K-Mart is really nice. I took
one lantern apart last spring with the intentions of beefing up the LED's, but the
driver circuit will only handle so much current. I still have one still intact.

greg

 

[[email protected]]

Well RS used to have stuff like that. Since they shut down my RS
I don't get there much anymore.

I still didn't hear a full purpose of this. The good dimmers use pulses to
control brightness, much more efficient. The switched dimmer as seen
on the $10 lanterns at the dollar store and K-Mart is really nice. I took
one lantern apart last spring with the intentions of beefing up the LED's, but the
driver circuit will only handle so much current. I still have one still intact.

greg

Ok, thanks for that. Iam going to try and find a dollar store lantern
like you said, although I don't recall seeing them anywhere of late.
I guess variable brightness would be just as good for this project.

 

[Michael Kennedy]

It may not work with a simple variable resistor because at higher
settings, the current will increase enough to probably just burn out the
small piece of the pot track that's still in circuit. A fixed resistor
will also still be needed to limit the full brightness current. In order
to get a decent control range, without risk of over-running the pot's
track and wiper, I would suggest that a small transistor needs throwing
into the mix to control the LED current, whilst the pot is left the
low-current job of controlling the transistor's base. If I get time today,
I'll give it a try.

Arfa

Arfa, How much current are we talking about here? If this is what I'm
immagining in my head with 2 or 3 led's it shouldn't draw much power. I
guess he could have one of those 5w led flashlights, but that was not what I
had in mind when he said dollar store.

Mike

 

[Victory]

Actually, I only want ONE LED in what I am building, so I guess that
might check things a bit. Just one LED is all I need for this
project.

 

[Arfa Daily]

Arfa, How much current are we talking about here? If this is what I'm
immagining in my head with 2 or 3 led's it shouldn't draw much power. I
guess he could have one of those 5w led flashlights, but that was not what
I had in mind when he said dollar store.

Mike

Hi Mike.
Well, if you reckon on a maximum current of say 20mA per LED, then for 3,
that's 60mA. Depending on what rail voltage he's figuring on running it
from, there's a good chance that if he was just using a pot on its own -
even allowing for still using any original limiting resistor - that when he
got towards the low end of his pot, he might be getting towards the
dissipation limits of the track and the wiper structure. Most carbon track
pots that you are likely to pick up at a 'general' electronics store, are
only rated to a few mW, and are not designed to carry current. There are
exceptions such as wirewounds, and some plastic tracked types. It just
seemed to me that the addition of a 20c transistor guaranteed that the pot
would not be damaged the first time it was turned up.

Someone mentioned pulse drive, which is the better way to do it, both from
linearity of control and LED life angles, but you are then into either a
specialist driver IC, or something like a 555 timer IC and a couple of extra
Rs and Cs and *still* the pot as well.

Arfa

 

[Arfa Daily]

Actually, I only want ONE LED in what I am building, so I guess that
might check things a bit. Just one LED is all I need for this
project.

You might get away with just a pot on a single LED. I guess for the cost of
one, it's worth giving it a try, but it does depend to some extent on what
rail voltage you are going to use to run it from, and the pot might not be
too long-lived if it is going to be regularly turned up and down. If it's
just a 'set and leave' project, you might be ok.

Arfa

 

[Dave Plowman (News)]

Arfa, How much current are we talking about here? If this is what I'm
immagining in my head with 2 or 3 led's it shouldn't draw much power. I
guess he could have one of those 5w led flashlights, but that was not
what I had in mind when he said dollar store.

The 'usual' LEDs found can only be driven to about 30mA from a constant
current source. So a 1/4 watt pot would likely be ok at the sort of
voltages found in a torch.