"Arfa Daily" wrote in message
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"Michael Kennedy" wrote in message
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"James Sweet" wrote in message
news:Y7Alj.8931$4b6.560@trndny08...

"Victory" wrote in message
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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.


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


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