LED Handling and Potentiometer Questions

[One AM]

Hi, all. I'm very new to this hobby, and to this site. I've recently obtained some LEDs and plan to light my first model, a PL D7. I have a few questions about using them, though. I notice that they are static-sensitive. Do I need to take any sort of precautions when handling them, such as one of those wrist straps used when working with the guts of a computer? Are there any precautions to be taken when soldering? Do I need soldering heat sinks? Is there a special kind of solder to use? Do I need to coat the leads somehow after assembling the circuit? I've read somewhere that cool melt hot glue guns are good for gluing LEDs in place, is this true?

I'm also looking for a potentiometer, and the ones at Radio Shack are all wrong for my needs. The problem is, I don't know anything about them, save their basic purpose. Can someone point me to a good one on Digikey or Mouser or a similar site that's good for 0 to about 500 ohms and is appropriately sensitive in its adjustability? I'll be using the pot to step down the intensity of my LEDs, as I purposefully got ultrabrights with this in mind. A quick outline as to just how to use one of these things (I am entirely without electronics experience, though I have done a lot of research) would also be very helpful, or a link to one.

Sorry for the huge number of questions. I'd really appreciate any help any of you can give me.

[tetsujin]

Hi, all. I'm very new to this hobby, and to this site. I've recently obtained some LEDs and plan to light my first model, a PL D7. I have a few questions about using them, though. I notice that they are static-sensitive. Do I need to take any sort of precautions when handling them, such as one of those wrist straps used when working with the guts of a computer? Are there any precautions to be taken when soldering? Do I need soldering heat sinks? Is there a special kind of solder to use? Do I need to coat the leads somehow after assembling the circuit? I've read somewhere that cool melt hot glue guns are good for gluing LEDs in place, is this true?

In order: Not really, I wouldn't bother. Not particularly. I don't think so. No. Not necessarily, unless you think there's a possibility of a short circuit otherwise. Probably.

[Scott Hasty]

In the 30+ years I've tinkered and used LED's I've never had a problem with static.

As far as pots, what style are you looking for, PC mount (horizontal or vertical), panel mount, power capacity, etc. Also, keep in mind, if you are mounting your pot inside your kit, you really should use a fixed resistor. You can buy a good assortment pack at Radio Shack for around $12.00. I use Mouser primarily as a source for components. They're hobby friendly (no minimums), their site is easily searchable and have VERY fast turnaround. I've have varied service from DigiKey and their site, well, sucks for searching.

I guess you could use hot glue for attaching, however, I'm not a big proponent of hot glue. It's isn't strong and when assembling a kit with wiring and lighting, you'll be manhandling it getting everything inside. Then, POP, your perfectly placed LED comes off. Creating a board and attaching your LED's to that is your best bet. I use breadboard and solder directly to the leads. This usually results in a nice, tight fit.

Scottie

[macfrank]

One thing about LEDs and potentiometers - always have a resistor in series with the pot. The resistor value should be calculated to be the maximum allowable by the LED for the voltage you're using.

This way, if you crank the power all the way up, the LED will still be protected.

[Madman Lighting]

BLUE leds are static sensitive, but not the other colors. At least the Panasonic ones I used for Ent-D a while ago sure were. I put them in on top of a coffee table during dry weather on a nylon rug. Those poor suckers flickered and died soon after.

If you're working on a metal desk or table, you're probably fine. The large metal mass will absorb any static zaps.

[Sparky]

The new blue and white LEDs and maybe even the ultra brights in other colors are labeled static sensitive. If the manufacturer labels it so you bet it is. I get the Electronic parts e newsletters and the last couple ones had mention of new white LEDs with high ESV protection. So they are getting them up to the same standards as CMOS chips. Use to be a time that if you ran your finger across your parallel port or serial port on the computer, it wouldn't work anymore. They got the ESV protection tech built up on the driver chips so its only a matter of time before the newer tech LEDs are as safe to handle as the older ones.

The pots you are looking for are multi turn, that way each movement is sweeping a smaller range of values.
take a look around the bourns web site, the instrument type pots are here:
<A HREF="http://www.bourns.com/components.aspx?c ... 99|3132787" target="_blank">bourns</a>

[One AM]

Thanks for the replies, everyone.

The package reads as follows:

"ATTENTION
OBSERVE PRECAUTIOS (sic)
FOR HANDLING
ELECTROSTATIC
SENSITIVE DEVICES"

Are the precautions as simple as a wrist strap, or do I need to do more, and, if so, what? I live in a fairly hot and dry climate, with occasional electrical storms (Utah).

Thanks for the link to the bourns site, but much of the specifications are confusing this novice. Would a 10k ohm, 10-turn pot do the job with the neccessary accuracy? I'm working with 18,000 mcd 5mm and 10,000 mcd 3mm LEDs, with the standard 3.6V 20 ma power draw.

EDIT: Would this (6639S-1-103 model) be a good choice?

A thought just struck me. Might I be better off with a variety pack of resistors and a breadboard?

[Scott Hasty]

A thought just struck me. Might I be better off with a variety pack of resistors and a breadboard?

Bingo.....

Scottie

[Sparky]

Wrist strap and a bench top that isn't static generating, or an anti-static mat. The resin/plastic folding table i use are terribly powerful static generators. when sweeping them after cutting and sanding plastic bits it is hard to get everything swept clean, big chunks of plastic leap from out of the garbage can to my hand, or the table or to the outside of the trash can.

[One AM]

Thank you very much, both of you. I've ordered a variety pack of resistors, and already have the wrist strap. I'll be working on an old wooden table and a cutting mat. I don't think that would be static generating... but I'm going off gut instinct there. Am I right?

That's my last question... at least, for awhile. I apologize for the really fundamental questions, but I couldn't find the answers for them. Perhaps I wasn't looking in the right place. Anyways, thanks again!

[Sparky]

I can't say for sure if the cutting mattes tend to hold static charges, or how much insulation effect the wood generates. There will be some charge held by both but mush less than the resin or vinyl covered partial board tables.

If you can find a big piece of anti static bay and clip it to ground that could be a make shift anti static mat, better than nothing.

The worst case issues with static/heat issues could be what happened with a side project a friend at work did. They had a bit of logic circuitry driving a sound FX circuit (model rail roading), and the circuit worked the first time they used it. This was their first time trying out CMOS chips (instead of TTL). The first test worked, then the next day it started acting funny, sometimes it would trigger sometimes not. It turned out the old soldering iron was not static safe. Basically it was generating voltages on the tip, as the tip on older irons may not be grounded, and since it's a heating element driven off house lines you can get some nasty voltages, low power but present, on the tip. CMOS circuits will take damage. Static damage can be complete or partial. Like a fuse that has started to burn through but hasn't gone completely. We had to watch a training video where they show scans of the connections inside a chip that have been static damaged but not destroyed. Ya we popped some receivers, I try to practice ESG safe handling, but when you're re-working boards the wrist tether starts to get in the way.

[macfrank]

If you can't find an anti-static bag, aluminum foil will do. Clip your wrist strap to a corner and you should be OK. Fold the corner so you have a thicker section of foil - so it doesn't tear.

You don't need to be grounded but you must be at the same potential as the static sensitive part that you're working on. What causes damage to a static part is a difference in voltage across the insulator in the semiconductor.

Static safe soldering irons are pretty common these days, and cheap.

[Sparky]

I think there might be some issue with grounding when you start using power supplies and soldering irons, these will be at ground and static charge floating in the system will start to flow to the ground.

A note on the static bags and wrist straps, they are actually not a direct ground they have several megaohms of resistance, so that you don't get a electrocuted from grounding your self, and your circuit board isn't shorted, since you will probably be doing powered test on the anti static setup.

PM me if you need a big anti static bag. we get our boards at work delivered in big bags, once its mounted in the chassis we don't need the bags and they usually get chucked. Also we have anti static mats on our desktops.

[en'til Zog]

All these precautions sound like good ideas.

Having said that, I've been working with CMOS cheeps and BLUE LEDs about as long as they've been available generally and haven't had any problems with any of them. (Knock on wood and/or laminated wood products).

Than again, I'm a big guy - big guys tend to sweat more than skinny little guys and tend to bleed off static charges better. Or so I've been told.