Dimmer switch on a LED ?

[Oldskool]

I currently have a 6-LED bulb under my trackball.

It is pretty bright, and MAY distract during gameplay (although I'm not yet sure as my cab isn't complete).

My mind is now focusing on bells and whistles, so I thought it may be a cool idea to add a dimmer switch for the LED.

A dimmer and a potentiometer are one and the same right?

The bulb is a 12 volt wedge style, that can be used in a car.

Any ideas on how to hook one up? I'm sure it's pretty straight forward, but I'm a bit clueless when it comes to things electrical.

[Druin]

I don't know how those particular things are set up but assuming it's just a bunch of LEDs set up normally, you can dim by using a potentiometer (making sure no matter what, that there will still be safe current limiting to the LEDs if it's not already built into that array)....or by getting fancy you may have success making the LEDs appear dim if you flash them at a certain fast rate so they are appearing to be on dimly.  The pot is probably the easier method and most impact.
So whatever your setup is right now to operate that LED system, just add a POT in series with one of the power leads and see if that allows control.   A 3 terminal pot, you would use the center wiper pin and one of either end, those 2 terminals to join into the broken power line.  

If you do see an effect with the pot but it's too drastic (lights go from on to suddenly off) then you need a smaller resistance.  And the POT should be able to handle whatever current this thing uses, probably not an issue...but otherwise you'll notice the pot gets warm.  

[Oldskool]

As I do not have an extra pot lying around, do you have a suggestion as to what I should buy?

100K perhaps?

[Beley]

more like 500ohms or less

[Santoro]

I am not sure on this, but I don't think it will work well.  I imagine a lot of the range of the pot will render the LED dark, with a narrow range where it lights up.

Unless you can get some super-sensitive pot....

I am not an expert though - give it a shot.  I'd be interested to see if it works.

[mp2526]

Your on the right track with the pot.  Here is a thread on another forum with some suggestions.

http://www.the12volt.com/installbay/forum_posts.asp?TID=29719&get=last

[Druin]

It's hard to say what value pot would work best, particularly since we aren't sure how that thing is wired up, it's not as easy as calculating current for a single LED and making a good judgement. WE don't know what kind of limiting is already built in, etc..

Basically LEDs (single ones at least) can run with normal currents between 5mA and 20mA depending on the LED, so on that thought, with a 12 volt source, 20mA and 10mA sort of target currents, you'd want maybe no more than a 2K pot to be sure you can limit all the way down to a few mA from 12 volts.  

But in reality there's probably current limiting built into that array, in which case you'd only need to really add several hundred ohms to the 12volt line, you'd have to experiment.

If you want the best suggestion to get you the most results from a single purchase rather than building up an experimenter's junk box,  I haven't been shopping in a while so I'm not sure what standard pot values you can easily get but try for something like several hundred ohms, and if you can't get one that low, try 1K or 2K but no more, you'll not get much range out of it because as someone said most of the adjustment span will be too-much limiting and you'll have an OFF led that suddenly goes ON near the end of the dial...no real tweaking....

Then what you do with that pot of a few hundred ohms, also get a FIXED resistor if necessary and put in series along wtih the pot, and that way by having most of the resistance fixed, and a small amount of adjustment on the pot, the pot becomes a more fine tuning element and you get more control for the full span of the dial with that small pot value.

The fixed resistor represents what WOULD be the unusable range of the single pot method where most of the dial is an OFF led, and the small pot expands the small usable region of the single-large-pot over a full dial now.  It's like zooming into the usable region of the pot.

So if you can find a pot a few hundred ohms, buy some fixed resistors around 100 ohms and you can connect them in series or parallel to get a usable fixed resistance that lets the small pot work well.   Two 100 ohms in parallel give you 50 ohms in case the 100 was too much the first try, etc.

Not knowing how the thing works, and knowing you have 12volts, just to be safe when experimenting I'd probably put 3 of the 100 ohm fixed resistors in series, along with the pot with its dial at center (in case you guess wrong about which end is 0ohms and full rating, better to have some resistance set), try turning the dial, if it's not lighting up take out a 100ohm fixed, try again...if you end up overshooting between different fixed resistor swapping sessions and you'd like something more fine in between, start throwing resistors in parallel there.


A final thought, if you want, you can use a larger value pot afterall, and avoid the problem of not having much usable dial range by getting a multi turn pot - instead of just getting about 270 degrees of one turn like normal, you can get a pot with 10, even 20 turns for full swing, and that way you do get a lot of control once you find the region that works....so you can try a 5k or 10k multi turn pot maybe...

That's about all I can think of

[Oldskool]

Great reply Druin....thanks.

I'll post back when I find something that works.