TEK NET
The Henderson Amateur Radio Club is pleased to present our Tek Net every Sunday evening, starting at 8pm local time (0300 UTC).
The audio portion of the Tek Net will be found on the Henderson Amateur Radio Club Repeater Network (RF). The audio may also be accessed via Echolink (W7HEN-R node 740644) and Allstar (node 44045).
The audio will refer to this page, so that the listener can more fully understand the concepts as they are presented.
All are welcome!
November 13, 2022
“All about LEDs and how to use them”
Recently I have been playing around with LED’s trying to come up with a high output or very bright LED display board for a project.
The progress that has occurred in the production of LED’s now days is remarkable compared to just 20 years ago.
I will lightly go over what a LED is, who invented which color ones and how the cost has changed because of the modern planar manufacturing process.
What is an LED?
A Light-emitting diode is an electronic component that emits light when connected to direct current only.
It works on electro-luminescent principle and can emit light in the visible spectrum as well as in the infrared and ultraviolet spectrum.
They are illuminated by the movement of electrons in a semiconductor material, usually aluminum-gallium-arsenide (AlGaAs)The light emits from the p-n junction of the diode.
They have characteristically low energy consumption, smaller size, longer lifetime and faster switching characteristics than incandescence lamps and because of that, they have a wide field of uses.
LED’s are extremely sensitive to current and should normally be used with a current limiting resistor to allow no more than 20-22ma of current to flow thru the p-n junction of the diode. There are IR LED’s that typically operate at 100ma and as much as a 1amp pulse, depending on the frequency and output.
When were the first LED’s invented?
This lighting effect was first discovered in 1907 by Henry Joseph Round, who worked for Guglleimo Marconi as a research assistant and was also an inventor, while experimenting with silicon carbide and a Cat’s whisker.
NOTE – Cat’s Whisker describes the contact between a extremely fine wire (“the cat’s whisker”) and the surface of certain crystalline material (normally silicon) to rectify and demodulate high-frequency alternating currents. (like rf signals on a receive antenna)
It wasn’t until 1961 when Robert Baird & Gary Pittman invented and patented an Infrared LED for Texas Instruments.This was actually an accident because the men were attempting to invent a laser diode at the time.
In 1962, Nick Holonyack invented the first visible light LED while working for General Electric Company. He used gallium-arsenide phosphide as the substrate which produced a RED light.
In 1972, George Craford developed the first Yellow colored LED for Mansanto Company and also invented a RED LED that was 10 times brighter than Holonyack’s.
It was in the later 1970’s that Fairchild Optoelectronics produced a low-cost LED device for manufacturers use (less the five cents each).
It was in 1976 that high-efficiency, high output LEDs were optimized for the use in optical fiber transmission wavelengths by Thomas Pearsall.
1994 was the year that the blue LED was invented by Shuji Nakamura, he also invented the white LED in 1995.
Since then, LED’s have gotten more efficient, much smaller-SMD size, higher output and much cheaper.
20 years ago a 10mm RED LED (5,000mcd) cost $5.85 each from Kiesub, now they are 10,000mcd and cost $.29 each, that’s a lot of light.
Let’s have some fun!
Below is a 400mcd (Milli-candelas) 5mm RED LED that was made before 2005.
I’m testing it using a 2032 Lithium battery with out a current limiting resistor because the battery current is less than the 20ma maximum limit of the LED.
Makes for a quick and easy way to check LED’s.
Below is a 2000mcd 5mm Red LED that was manufactured in 2018 being tested with the same 2032 battery.
Here is a 6000mcd white 3mm LED and the output is very bright and is only drawing 6.8ma of current.
As we see here, this Infrared LED is drawing 21.6ma at full output.
Look closely at the junction in the diode, you can just barely see a slight red glow from the junction.
Not all IR LED’s can be seen by the human eye like this one, it is determined by the maker’s process and also the wave length transmitted.
Want to know if an IR LED is really ON, just turn on the camera in your cell phone and point it at the LED, the CCD camera will see it easily. (go ahead and try it with the TV remote and your cell)
What can you do with LED’s?
Obviously they make great Power-ON and activity indicators on your electronic equipment, but you can use them in other ways also.
For example…want to know when a battery voltage or power supply voltage goes below a certain level, look at one of the circuit diagrams below. (diagram F)
On the right is a seven segment LED display.
They are also made with 14 segments to produce alphanumeric (A-Z) character displays.
How about making a invisible audio transmitter/ receiver, you can do that to very easily.
