To start out, I'll mention that most LEDs require between 2-3.5V. Because you will be wiring them to 5V or 12V, you will need to resist the current flow in the circuit, so you don't overpower the LED. This is the purpose of a resistor. The resistor can be on the positive or negative side of your circuit, because it will resist the current either way. You should almost always connect LEDs to 5V, because that is already more than enough power for a 3.3V LED.
For a 3.3V 20mA LED, which is a good standard, a 100 Ohm 1/4W resistor wired to 5V is recommended. 2.1V 20mA LEDs will need a 150 Ohm 1/4W resistor per LED. Contact the distributor of the LEDs you bought for specs of your LEDs. Generally Red, Yellow, and Orange are 2.1V and all others are 3.3V.
It is also possible to use just one resistor in a circuit to power multiple LEDs. The two variations of this are parallel and series. Generally you will always use parallel, because with series, the Voltage required multiplies, so if you attempt to power 8 LEDs in series, it will require 26.4V (8*3.3).
You can always use a resistor with higher Ohms and higher Wattage, but the higher in Ohms you go, the more dim the LED(s) will be. The higher the wattage, the bigger the resistor, but it will not affect your LEDs at all. Never go under the recommended Ohms or Wattage though.
Some notes to take away from this tutorial:
- Unless special circumstances are required, you should always wire to 5V (red wire).
- Unless the supply voltage is the same as the required voltage, you WILL need a resistor.
- The resistor can be placed on the positive or negative side of the LED.
- You can use 1 resistor per LED, or wire in parallel or series and use 1 resistor for an entire circuit of LEDs.
- Never use a resistor under the recommended Ohms or Wattage.
- Click here to use our resistor calculator to determine the correct resistor for your needs.
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