Wiring LED to Driverstation

[Robert Cawthon]

Originally Posted by Alan Anderson

Different LEDs have different forward voltage drops, and work best at different currents. That's why you will need different resistor values for different colors.
"

Could you point me to something that would tell me what resistances are required for which color? I am not extremely knowledgable about electronics design, but I can wire things up and solder them if given the design. This may be my first foray into design during the off season.

[ay2b]

Originally Posted by Robert Cawthon

Could you point me to something that would tell me what resistances are required for which color? I am not extremely knowledgable about electronics design, but I can wire things up and solder them if given the design. This may be my first foray into design during the off season.

Read the spec on the LED -- it should give you a current and a voltage rating. The voltage rating will probably be somewhere in the 1.5-3.0 volt range; the current rating will probably be somewhere in the 10mA-60mA range. Suppose you have a 2v, 30mA LED.

Suppose you have a typical 5v supply, like on the driver station. Some of that voltage is "used up" by the LED, and some is "used up" by the resistor. The current through both will be the same. If the LED takes 2v, then the resistor takes 3v, to make the total of 5 from the supply. The Voltage/Current/Resistance formula is "V = I * R" (where V = Voltage, I = Current, R = Resistance). In our example, the voltage drop across the resistor is 3v and the current is 30mA (or 0.03A -- always make sure you get your decimal points right). 3v/0.03A = 100 ohms, so you would want a 100 ohm resistor.

I picked example numbers to make the math easy. If you get some value for a resistor and can't find common resistors with that value, just pick something close. The brightness of the LED is related to the current through it. If you pick a resistor which is too small, then the current will be higher and the LED will be brighter (and burn out sooner, up to the point of burning out right away). If you pick a resistor which is too big, then the current will be higher and the LED will be dimmer.

[Jared Russell]

Originally Posted by Robert Cawthon

Could you point me to something that would tell me what resistances are required for which color? I am not extremely knowledgable about electronics design, but I can wire things up and solder them if given the design. This may be my first foray into design during the off season.

Robert -

Wikipedia has a decent list of colors and voltages here. If you have documentation for your LED, I would go with that, but if you don't this should give you some hints.

[Al Skierkiewicz]

Robert,
As you can see from the above reference, most LEDs are near 2 volts when turned on. The exceptions are the blue and white and combinations of those. To make the resistance calculation, subtract the LED voltage from the power supply voltage. In our case, 5volts-2volts(LED)=3 volts. This is the voltage the resistor must drop. A good rule of thumb for most general purpose LEDs is 20ma. Using Ohm's Law solving for resistance R=V/I=3/20ma=3/.02A=150 ohms. 150 is a standard value of resistance but if you can't find one, 180 ohms is also a standard value. Using Ohm's law for current I=V/R=3/180=.016=16ma. Although the LED would be not as brite at 16ma, you might never see the difference. As pointed out in the documentation, the output circuitry is limited to a maximum amount of current so using the 180 ohm resistor is better for the circuit but gives a dimmer output for the LED.