Optoelectronics

LEDs

LEDs are diodes that have a voltage drop designed to produce visible light. When using a LED in a cicuit it's important to use a current limiter such as a resistor. A typical LED is designed for aproximately 10mA. 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.

LCDs

• 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.
• MatrixOrbitral - Specializes in serial display especially the type for direct connection to a PC.
• Jameco - A small selection. Mostly serial.