LED Primer

Introduction

Like normal diodes, Light Emitting Diodes (LEDs) are semiconductor devices designed to conduct current in one direction only. What makes LEDs unique is their internal material makeup: when atoms in an LED release energy due to the flow of forward current, it is released in the form of photons (light). Different construction materials and various phosphor coatings are used to produce numerous colors of light.

LEDs that Phidgets sells are all operable via the digital outputs on any of our interface kits. However Phidgets also sells a specific LED controller since it is often desirable to control more LEDs than even the 0/16/16 can operate.

Controlling LEDs

Forward Voltage

The materials used within LEDs that cause them to emit different colors of light affect a property called its forward voltage. The forward voltage is the voltage at which current in the forward direction will flow through the device and allow the LED to convert electrical energy into light. If the voltage applied to the LED is below the forward voltage of the LED, very little current (or none) may flow, and therefore very little light will be emitted. Most standard LEDs with colors such as red, amber, orange, yellow, and green have forward voltages below 2.75 Volts, and can be used with the PhidgetLED by simply soldering them to a connector-wire and inserting the wire into any PhidgetLED board connector. The forward voltage will default to 2.75V, and the maximum current defaults to 20mA.

Supply Voltage

The 1031 is capable of adjusting the forward voltage supplied to the LEDs with 1.7, 2.75, 3.9 and 5 volts settings allowing you to properly drive blue, white, violet, ultra violet and purple LEDs. The supply voltage will affect all LEDs. If you set the supplied voltage too high, power will be wasted and the PhidgetLED may shut down from thermal overload. If you set the supply voltage too low, your LEDs will not be driven at the requested current, and will be dim or nonfunctional.	Template:Table border = 1	Typical Forward Voltages	'
Color	Forward Voltage
Infrared	< 1.9
Red	1.7 to 2.2
Orange	2.0 to 2.2
Yellow	2.1 to 2.4
Green	2 to 2.3
Blue	3.2 to 4.0
Ultraviolet	2.1 to 3.8
White	3.3 to 3.6

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