Electronics Q

RatLabGuy

RatLabGuy

You look like a monkey and smell like one too
Joined
May 18, 2005
Location
Churchville, MD
I'm building a very simple circuit and need a little help.

Lets pretend you have several LEDs connected to a single power source (in parallel), each is switched on/off via a relay.
The power source is 12v, so it needs to be dropped to be usable by the LEDs (5v max, 2.2v min). I want to be able to manually adjust teh intensity of the LED light, so I was planning to just use a linear potentiometer to do that.

One thing I wonder about thoughis what will happen when multiple LEDs are turned on. Will the added resistance cause a drop in the available voltage (behind the pot), and hence affect the luminance of other LEDs?

If so, would using variable linear voltage regulator be better than the pot? What's the advantage/disadvantage of each?
 
The amount of voltage drop provided by the pot is dependant on the load, so yes, it could affect them. OTOH, it might be insignificant enough to where you wouldn't notice it?

Do make sure you can't overdrive the LED's by mistake by turning the pot up too far... Maybe a resistor in front of the pot would be a good safety measure... (Unless the pot's adjustment isn't easily changed)

Also, you said turned on by relays.. you mean transistors? relays would sooooo be overkill! :lol:

I haven't messed with the linear's you mentioned, so no input on that, sorry..
 
Yeah I know about overdriving the LEDs. Actually I'l probbaly have a main pot or resistor to get it down to 5v, then uset he other for the tuning.

Yes, turned on by relays. Yes, a complete overkill. But, I'm (obviously) not an engineer nor do I have time and patience to spend much time soldering circuits together. So I bought a pre-made card/kit that already has a 25-pin parallel interface connected to 8 relays, so you can easily open/close a channel by plug 'n play. The only reason that is even needed is that the parallel port cannot supply the current needed to turn on > ~2 LEDs (spec is only like 80mA max).
Could not find a similar device w/ transistors... but for future reference if anybody knows of one I'd use that instead...
 
if your source V is 12v, then you will need to put a resistor inline to knock down the voltage, and then use the POT to dim.

I added som LED's to my dodge console. 2 Leds in series with a resistor to knock down the voltage, and I wired to to the dash lights so they would dim with the rest of the lights.
 
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