Light-emitting diode

A light emitting diode is the most popular kind of optoelectronics.

To make the LED light up, you need a power supply (any voltage) and a resistor.

The resistance required is as follows: R = (U_power - U_led) / I_max

Example: a LED with voltage drop of Uled=1.2V and a max current of I_max=0,020A (20mA) to be powered by a 5V DC source needs:

R = (5-1.2)/.02 = 190 ohm

You then connect a 190 ohm resistance in series with the LED to make it work.

POV

POV display

throwies

Several other wiki discuss how to turn LEDs into "throwies"(little blinking LED devices that attach to outdoor structures via magnets):

• Cybords wiki: Throwie Talkie: A Talkie is a Throwie that has been hacked to blink graffiti messages in Morse code.
• TagRecord.com Wiki: Led throwies
• the mayowiki: Throwies

sensor

A few people use LEDs in an unusual way: as sensors.

light pipe

Many people want and blinking/glowing spot *here*, controlled by a nearby circuit board *there*. One approach is to put a LED directly on the circuit board *there*, and guide the light from that LED to *here* using a light pipe.

Some commercial off-the-shelf light pipes; and some tips on building custom light pipes from transparent acrylic, aluminum foil, or 3D printed materials:

• "LED light pipes" [1]
• "LED light pipes" [2]
• "Build Your Own Light Pipe" [3]
• "3D printed light pipes" [4]
• "Care222 LED Lamp " [5]
• "3D Printing Light Pipes" [6]
• "Using t-glase for Light-Pipes" [7]
• "Light Guide Techniques" [8]
• "Optical light pipes" [9]
• "Light Pipe Selector Guide" [10]
• "LED light pipes" [11]

5.0v - 3.3V voltage drop via red LED

The average red LED has a 1.7V voltage drop. This property can be (ab)used to power very small 3.3V IC's from a 5.0V power supply -- put the LED in series with the 5V line. There probably won't be enough power used to light the LED properly, but this does not matter for the voltage drop property.

further reading

LEDs used normally: to emit light:

http://en.wikipedia.org/wiki/LED

LEDs used "in reverse": as light sensors:

• Hack a MiniPOV3 for IR capture
• Making an Amplified Color Sensor from an LED and an Op Amp
• LED1 LED Sensor Relay Tracker Schematic
• "What are the relevant parameters for a reverse-biased LED light sensor?"