Electrical

From HBRC WIki

Basics

Iguana Labs Beginner Tutorials link is dead

This looks like an interesting reference for electronics:

• http://www.allaboutcircuits.com/

LEDs

LEDs want about 20 to 25 milliamps current max. The equation required here is:

Voltage = Current * Resistance or V = I * R

so for a 12 volt source and an LED you have:

12 = .025 * R

Solving for R

12 / .025 = R

480 = R

So you need a 480 ohm resistor.

Each LED drops about 1.4 volts (it differs by color) so if you hook up 6 in series you would see a 8.4 volt drop in voltage across the LEDs. That would mean that you would want the resistor to drop 3 to 4 volts.

Plugging that into V=I*R we get:

4 / .025 = R

160 = R

So a 160 ohm resistor would work with 6 LEDs in serial. But generally LEDs are pretty forgiving so pretty much anything in the 160 ohm to 480 ohm range would probably work. The higher values would give you a dimmer light.

by Chuck

I recently received a "cheat-sheet" for LEDs from a distributor Sure-Electronics.com ... it seems very useful for standard LEDs;

Recommended Resistors 1/4 Watts for Blue, Green, UV and White LEDs

   5V =  82 - 100 ohms
 7.2V = 220 ohms
   9V = 330 ohms
  12V = 470 ohms
13.2V = 560 ohms

Recommended Resistors 1/4 Watts for Red, Yellow, Orange and Pink LEDs

   5V = 180 ohms
 7.2V = 270 ohms
   9V = 390 ohms
  12V = 560 ohms
13.2V = 680 ohms

Now we need similar charts for higher current LEDs like 1W, 3Watts and Lasers.

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Another interesting tidbit on LEDs is I have some triplet LED strips ... the strips come in lengths I think either 25 foot lengths or 250 LEDs per roll and you can tie a 12V source to one end of the strip and the whole thing lights up and looks really cool. Each 3 LEDs is in parallel with the next "triplet" LEDs along the entire strip ... and you cut them down to lengths at the "triplet" markers.

The strips are designed to be used for stairs and pathways etc... but I'm using shorter lengths of them on my robots. Each section of the LED strip is 3 LEDs ...

- 9V to 12V source ties to the - on the 1st LED ... the + on 1st LED goes to the resistor (values by color in above table) then to the 2nd LED - and then the 2nd LEDs + side goes to the 3rd LEDs - and the 3rd LEDs + side ties to + 9V to 12V source again.

I got the LED Triplet strips from Mike Bosco mbosco@lanetechsales.com

http://lanetechsales.com/

But I also found using that:

-Source - LED + resistor - LED + - LED + Source+

series circuit works with standard LEDs too.

by Walt Perko