Calculating resistor and battery pack size when using individual LEDs
Note: Read this section only if you are soldering your own circuit using individual LEDs.
If you are soldering your own circuit using individual LEDs, you will have to pick an appropriate battery pack and resistor based on the current and voltage requirements of your LEDs. You can find this information in data sheets or on the vendor's website (for example, this red LED from Jameco Electronics). A typical LED will require about 20–30 milliamps (mA) of current and between 2–4 volts (V) depending on the color, but you should always check the exact value for the LEDs you plan to use.
To select a battery pack, you need to know that a typical AA or AAA battery provides 1.5 V. Battery packs combine the batteries in series to increase the voltage, so a double AA (or AAA) battery pack provides 3 V, and a triple AA (or AAA) battery pack provides 4.5 V. So, whether you need two or three batteries depends on whether your LEDs require less than or more than 3 V to operate. Important: This assumes you will be wiring your LEDs in ...