LED basics?

[Black Diamond]

Anyone know of a couple good sites to go to where I can learn how to wire LEDs? I'm sure it's kinda simple, but I have no experience so I'm looking for something that doesn't require an electrical engineering degree to grasp.  I've done all kinds of decoder installs so I'm pretty comfortable soldering small wires and such.

Thanks for any help.

[Nelson]

All the basics in an easy to understand format:
http://www.kpsec.freeuk.com/components/led.htm

[engineshop]

If you looking at SMD LED, you need to download the spec sheet of the manufacture since each SMD LED has the cathode on a different spot.

[bsoplinger]

That is a good site, all the info in 1 place, well laid out.

I should reiterate a point made on that page for the persons new to using LEDs (although the site does have it in red lettering to make it stand out):

If LEDs are in parallel each one should have its own resistor.

I've seen enough blown DCC installs where someone put 1 resistor on the blue lead and then wired 1 led to white and another to yellow (F0F and F0R lights) and then both to the blue lead with the one resistor. Like the article says, resistors are cheap. If you are really pressed for space, you can get 1/4 W SMD (surface mount) resistors from Ngineering.com, also available from Walthers. Although small, they aren't too tiny that I don't think the average person couldn't solder them by hand. It is cheaper to buy your resistors from an electronics shop but you'd be needing to buy other things to get to the minimums most sites have since resistors in bulk are in the few penny range pricewise. Even SMD resistors get pretty cheap in reasonably small quantities (like 50).

[Black Diamond]

Thanks guys. I'll be using the surface mount leds.

[amato1969]

BD, let us know how your surface mount installs go.  I have not yet tempted the soldering gods with those tiny LEDs.  I have a good stock of golden-white LEDs from Loys, and a good assortment of resistors from the Shack.

My best advice is to always use flux, so that the solder flows quickly.  Otherwise you will risk overheating the LED.

[DKS]

Based on experience working with SMD LEDs, my suggestion is to stick them face-down to double-sided tape on a smooth work surface to keep them secure while attaching leads. Use a temperature-controlled iron with the finest pencil tip you can find, and keep the tip tinned and clean. Pre-tin the wire before soldering it to the LED; then you should be able to make the connection with one brief touch of the iron tip (I've found that most SMD connection pads are either already tinned or will readily accept a solder joint with no preparation).

There are lots of places to put SMDs to use. Here are some I attached to a brass crossing gate. This made assembly pretty easy, since I could solder one terminal of the LEDs right to the arm, which kept them solidly in place. I used fine solenoid wire for the other lead.

[mmyers]

Based on experience working with SMD LEDs, my suggestion is to stick them face-down to double-sided tape on a smooth work surface to keep them secure while attaching leads.

This is great advice. I've had good luck soldering SMD LEDs. No luck finding them after they go airborne.

Martin Myers

[engineshop]

I use a smooth clips attached to a mini vise for my SMD LED soldering. Of course also a OptiVisor but that is because of age.

The clip acts as a heat sink and keeps the SMD cooler while I solder the magnet wires to the contacts.

[engineshop]

Oh by the way,
David I love that railroad crossing gate.

[Black Diamond]

More good tips, thanks guys. As soon as I find suitable housings for the leds I can start experimenting.

Any pics of the crossing gate lit up dks?

[DKS]

Oh by the way,
David I love that railroad crossing gate.

Thank you!

Any pics of the crossing gate lit up dks?

Regretfully, the only one I have right now is this blurry video frame grab of a different crossing gate--



The SMDs are wired to flash the same way as the real thing: the center light alternates with the other two. The SMDs are powered by a circuit that alternates the polarity of power at 1 Hz, so only two wires are needed for the entire crossing gate assembly. Although it breaks the rule of not wiring LEDs in parallel, they all work perfectly since they all have the same specs (or close enough).

Here is another version of this gate:

[dnhouston]

Great tips on the SMD's.
and David, awesome work on those gates!