basic potentiometer wiring

Hey all,

I'm working on a project with some LED's.  I'm considering using a 1K, 3/4W potentiometer (technically a trimmer) to dial down the amperage in a parallel circuit and eliminate the need for ANY individiual resistors at each LED.  If I can dial the resistance up to about 630 ohms for 10 LED's, then I don't need 10 LED's.

My question is this:  How do I wire up a trimmer to fulfill this purpose?  It has three pins, with pin 2 being the "Wiper," but I'm getting conflicting reports of what to do with pins 1 and 3.  I want to use this on the POWER side of the 12vdc circuit.  I've read that pin 1 goes to positive, pin 2 goes to my load(s), and pin three to ground??  but doesn't that mean that between pin one and 3 I need to drop 12 volts?  That'd make the potentiometer/trimmer work like a load resistor, and at only 3/4W, it'd melt the thing to a puddle in roughly 5 seconds.

Can you guys provide some guidance?  Thanks.

Jeff

I, personally, would only use pins 1 and 2 and leave 3 unconnected.  This will turn the "trimmer" in to a variable resistor.  For best results find the absolute max amount of current you will ever need and put a resistor of proper value in series with the pot.  That way, if the pot is dialed down to 0 you won't blow the LEDs as the other resistor will limit the current to your absolute max value.

One thing you should consider doing is using a 7805 voltage regulator instead of 12vdc - this will allow the LEDs to maintain their brightness even as battery voltage moves around.

As far as hooking up power to pin 1 and pin 3 you will be turning the pot in to a load resistor - however at 1K ohms you will be well below your 3/4watt rating at 14.4vdc (.21 watts).  The pot will be fine.  Between Pin 1 and Pin 3 you will ALWAYS have the total resistance of the pot (so 1K no matter when the dial is turned).  The wiper is then resistantly proportional to the dial position (and inversing proportional between pins 1 and 2 and pins 2 and 3.  So, say you have 200 ohms between pins 1 and 2 you will always have 800 ohms between 2 and 3.  Another way to say it is the resistance between Pins 1 and 2 plus the resitance between pins 2 and 3 will always equal the total resistance of the pot (the resistance between pins 1 and 3).