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. Note: this page could use a lot of work, can you help?

ElectroLuminescent Wire

See EL_Wire

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
• sensor -- the multi-touch display#bidirectional LEDs article section describes how to use LEDs as a crude light sensor.

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
6. Online LED store with good shipping rates
7. Some thoughts on throwies interesting notes on the resistor normally used with an LED.

LED Arrays

Lots of LED arranged in a rectangle. Useful for displays. Getting cheap now. Sometimes controlled by row and column time division multipluxing.

• 2416 Dot Matrix Red Display information Board 24 by 16 led for about 12 bucks.
• PointLess LED Array
• Some multi-touch displays use LED arrays
• 64 LED Button Pad 8x8 array of RGB-LED-lit buttons, plus PWM drivers, designed to be driven by an Arduino-compatible board ... such as the 8x8 RGB LED Matrix driver
• 4x4 RGB LED Shield Arduino shield
• Mignonette game kit 5x7 bi-color LED matrix and ATMega88 processor [1]
• Meggy Jr RGB LED Matrix Game Development Kit

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.

• Bare glass - These displays do not have built-in controller and are essentially LCD glass with contacts for every segment and backplane. You need a special driver (e.g. PCF8562) to use these or a microcontroller with built-in LCD controller (e.g. ATMega169), however, displays with only one backplane could be driven directly from the microcontroller I/O pins or bank of shift registers which is more convenient (atmel has an appnote on this method). The advantage of this display type is its price - it is not much different from 3-4 digit LED matrices, and it surely outperforms LEDs in terms of power-efficiency.

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.
• Topway LCD - supplier from Shenzhen, Mainland China
• http://store.gravitech.us/lcds.html
• TVI Electronics

LCDs are extremely commonly used as a Microcontroller User Interfaces. In particular, watch displays are small displays suitable for Open Source Watches -- most of them are LCD displays.

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

Also known as solar cells.

1. Photovoltaics - Wikipedia, the free encyclopedia
2. Solar Cells
3. http://www.eevblog.com/2009/12/04/eevblog-48-solar-power-hope/

VFD: Vacuum Flourescent Display

Numeric, Alpha or special display.

• life time - around 10000 to 30000hrs when dim down to 50% brightness
• make sure no any dead pt
• update rate - around 10mSec for each new update data
• command for dim down
• no electrostatic effect due to glass material

Salvage from many microwave ovens and other consumer equipment.

• VFD Module Character Displays

Other Reading

• Optoelectronics and optics page