Very cool project, and great advice from Lefty.
Just wanted to add some LED basics.
- The LED will be defined by its output brightness in millicandles. Its tough to quantify except to compare LEDS to each other , the more mcds, the brighter it can be.
- The LED will have a rating called Vf. This is the forward voltage, how much volts it takes when turned on ( positive voltage applied to the anode + side ).
If the LED has a Vf of 3 volts, & If the arduino drives it with 5 volts, there are 2 volts leftover that have to be used by a resistor ( if a device regulates the LED current, the resistor isnt needed.) it takes knowing #2 & #3 to pick a resistance. - The LED has a rating called If - this is the continuous forward current. If the LED is driven to ON, and stays on for several seconds or more, you want to keep the LED under this rating to not eventually burn it out. to pick this resistor if there are 2 volts leftover for the resistor to use, divide by the If ( in mA) to pick the resistor in kilo-ohms. For example, if If = 20 mA, 2 V / 20 mA = .1 kohms ( that is 100 ohms ) for prototyping arduino projects, I generally just use a 220 ohm resistor for indication.
- If the LED is used in a for short times like in a scanned or pulsed circuit, there is a maximum value for current called Peak Forward Current ( for example 1/10th duty cycle, 0.1ms pulse width) where the resistor can be sized using the peak current value that is much higher, for example 70 mA ( 3 1/2 times the continuous rating ) and the resistor value can be much smaller to allow this peak current.