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":

• 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.

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.

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?"