LED's (Light Emitting Diodes) are the beautiful little solid state light bulbs that have many uses. They are used in small flashlights, home lighting, indicator lights, remote controls, stop lights, and graphic displays. They come in many sizes and colors. They are available in infrared (for remote controls) or ultraviolet (for testing money). Some of them have a built in circuit that makes them blink or vary color. RGB LED's are composed of red, green, and blue which allows them to display a rainbow range of colors.
Below are some projects using LED's that start at a basic level and then move on to more advanced applications.
LED's are semiconductors, and as such they are sensitive to heat. Applying too much voltage for too long a time will literally melt the silicon they are composed of. Most small LED's are designed for a current of about 20 ma. Some can only tolerate 10 ma, so be sure you check the rating when you buy the led. The easiest way to control the current is to control the amount of voltage that will drop across the led with a resistor. The circuits below show the resistance needed for common voltages.
Common Resistor Values
The schematic above shows common resistor values in ohms that are needed at different voltages. White LED's require a higher voltage so they generally need a lower value of resistor to run at 20 ma.
LED's often come in a clear case or with a lens that can only be easily viewed within a narrow angle. It is easy to widen the viewing angle by simply using a power sander to flatten the lens of the led. You can brighten it further by first painting the led with white paint before you sand.
This is particularly useful when using RGB LED's that are water clear. You will get a better mix of colors, especially white, if you first paint and then flatten the led.
A Gooseneck Reading Lamp
Here is a simple project using white LED's to create a 12 volt lamp. These LED's give off a very nice light that is suitable for reading. You can use any number of LED's, but I have found that the minimum for easy reading is around 24.
The gooseneck is made out of 12 gauge Romex of the type used to wire houses. For the housing on this one, I used an end cap for 4" PVC pipe, but you could also use a shallow tin can.
Led Projects with Microcontrollers
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