Optoelectronics

Optoelectronics are devices that are some combination of electrical and optical. Perhaps the simplest is the Light Emitting Diode or LED which converts electrical energy into light. A listing of some optoelectronic devices follows.

LEDs

LEDs are diodes designed to produce visible light.

Commonly a small low power device that makes a not too bright light. High power, high brightness versions are now becoming widely available. The low power ones typically run on a volt or so, at about 10 ma. Typically they are run on higher voltages with a current limiting resistor that sets the current. Current control is almost always required ( often with a resistor ) as LED are very sensitive to small voltage changes. Like other diodes they conduct only in one direction.

When using a LED in a cicuit it's important to use a current limiter such as a resistor. When using resistors measure the foreward voltage drop of the LED with a multimeter, subtract this from the supply voltage, then plug the difference into ohms law to calculate the required resistor value. Different color LEDs all have different voltage drops.

Uses

• Indicator
• Part of 7 segment display
• Light source

External Links

1. Light-emitting diode From Wikipedia, the free encyclopedia
2. Learning About Transistors and LEDs
3. Brighter Appearance through pulsing
4. Improving the Ping Pong Ball LED Diffuser
5. Basic_Circuits_and_Circuit_Building_Blocks#Light_Emitting_Diode_.28_with_current_limiting_resistor_.29

LCDs

Liquid Crystal Displays

• Serial - These displays have a microcontroller on the display with a serial or I2C connection. Several builtin fonts are typically included. These displays are very easy to use, but the update rate for a display is very slow. Fullblown bitmap support is usually not available. Typical price for these displays is $50+.

• Parallel - Parallel displays connect to a microcontroller via a parallel interface( the bitwidth varies from 8bits to 32bits ). Displays can have a much faster update rate then serial since they allow arbitrary graphs to be display. The displays are typically much cheaper then serial display starting as low as $20.

Finding LCD displays is not easy since huge distributors such as Digikey have a limited selection.

Some places that do have LCDs for hobby use:

• Sparkfun - Has a good selection of both parallel and serial displays.
• MatrixOrbital - Specializes in serial display especially the type for direct connection to a PC.
• Jameco - A small selection. Mostly serial.
• Seeedstudio - Free sourcing services with some stock of basic LCD.

Photo Diode

A diode with its junction exposed to light will generate a little bit of voltage and current ( if the circuit resistance is not infinite ). Diodes that are meant to exploit this are photo diodes, regular diodes often, but not always, are enclosed to keep out the light. The signal is not strong and lots of amplification can be useful.

Photo Transistor

If a photo diode makes up one junction of a transistor the photo diode has a built in amplifier. This is the photo transistor. An advantage is that the signal is larger.

Photo Multiplier

This is a somewhat unusual ( for most experimenters ) device. It is a vacume tube with a series of electrodes at high voltage from each other. When a photon knocks an electron out of the first electrode it then knocks out more on the second electrode and so on. They can be very sensitive, I think down to single electrons.

Photovoltaic Cell

1. Photovoltaics - Wikipedia, the free encyclopedia