How to Use an LED as a Status Indicator

By eHow Computers Editor

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LED, or light emitting diode, is the name of the tiny light bulbs that are commonly used in electronic devises that indicate if a device is plugged into a power source and displays the status of the device. The lights are just bright enough to be seen, but not bright enough to use as a source of light or luminescence.

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Instructions

Difficulty: Easy

Step1

Go to your local electronic component store and buy LEDs. LEDs are organized into 3 types, miniature, alphanumeric and lighting. The type most commonly used for status indicators are miniatures. To build a simple circuit, purchase a photo transistor, regular transistor, resister and battery along with your LED.

Step2

Evaluate the amperage that you anticipate using with the indicator. Indicator LEDs usually work with low voltage DC current through a current limiting resistor. The most commonly used currents for status indicators are 2 mA, 10mA and 20 mA. If you are considering lower currents, remember that the efficacy is reduced as the current lowers.

Step3

Make a simple indicator by soldering the wire from the top of the resistor to the base or middle wire of the transistor. Then solder the bottom wire from the resistor to the collector or far right wire of the transistor. Solder the wire on the flattened side of the photo transistor to the collector or middle wire of the transistor.

Step4

Add the LED by soldering the positive wire from the LED to the emitter wire on the transistor. This is the wire on the left and the only one without anything connected to it. Solder the other wire to the emitter on the wire with no other connections. To view the light, run the circuit or turn on the device.

Tips & Warnings

A soldering iron is required for this project. Be very careful as they generate a lot of heat. Do not leave unattended, especially if there are any children or pets in the house.