A Couple Of N00b Questions

[railhead]

I'm wanting to make sure I'm clear on a couple of things before I slap on the solder. What I'm doing, is building a simple ABY switch based off of the layout made available by Mike Fuller at Fulltone (http://www.fulltone.com/PDfFiles/AB_switcher.pdf) -- and yes, this is my first build. Here's a shot of the layout:



My questions are about the wiring of the LED resistors...

1. Since I'm coming off the positive 9v, I need to attach the resistor to the anode of the LED, right?
2. In the pic, he's "chaining" from one anode to the other -- but what's he using? Did he just take the leg from one resistor and span it across? Can't I just use wire to chain them?
3. Isn't the anode on a resistor always the longer leg?

Thanks!
Maury

[snoof]

1. doesn't matter which one you use.

2. yes, leg of one resistor, sure you can use wire.

3. on 5mm LED's, the cathode is the side w/ the flat spot on the LED itself.  can't remember how to determine using lead lengths.

[GREEN FUZ]

This should help.

http://en.wikipedia.org/wiki/Light-emitting_diode#Considerations_in_use

[axg20202]

The way I remember long versus short (positive versus negative) leads on LEDs, electro caps etc, is that the longer lead is positive because there's 'more' lead and the shorter lead is negative because there's 'less' lead.

[Mark Hammer]

Since you have room in there, you may want to consider using a trimpot to be able to adjust LED brightness and current drain.  With the advent of a wide array of superbright LEDs, simply using the old tried and true 2k2 resistor or similar may be insufficient to have a status LED that doesn't sear your retina every time yo walk by.  Consequently, a 1k fixed resistor in series with the wiper of a 10k trimpot can be helpful to dial in how bright you want the LED to be.  If you install a low brightness unit in there, the minimum resistance value of 1k is low enough to squeeze enough light out of the LED.  If you stick a high brightness unit in there, the max of 11k is sufficient to "tame" it.

Alternatively, if you use two different-coloured LEDs to indicate which output is presently active, there may be a discrepancy in brightness between them.  Using a trimpot to balance out their brightness, relative to each other, might be useful.

[railhead]

Thanks for the quick replies.

1. I guess the LED doesn't care which is + and which is - as long as the + gets the resistor, since all it's doing is allowing basic current to flow through?

2. RE: a trimpot -- that's a great idea. Do you just place a trimpot in-line like: pos current > pos lug on trimpot > resistor > LED > - lug on trimpot > switch? How do I now which Ohms to get?

Thanks again!

[GREEN FUZ]

Thanks for the quick replies.

1. I guess the LED doesn't care which is + and which is - as long as the + gets the resistor, since all it's doing is allowing basic current to flow through?

If you want it to light up it needs to be the right way round.

[snoof]

Thanks for the quick replies.

1. I guess the LED doesn't care which is + and which is - as long as the + gets the resistor, since all it's doing is allowing basic current to flow through?

No.  The LED doesn't care witch lead the resistor is on, it def cares witch is pos and neg.  Like Fuz says, you gotta hook it up proper to work.

[railhead]

Okay, that makes sense -- I misunderstood snoof's first response.

[railhead]

So what about the trimpot question?

[snoof]

batt + >1k res>10k trimpot wired as variable resistor>LED's pos lead