# Brief switch controlled indicator LED circuit

Lighting an LED is a simple circuit that is a part of many demonstration circuits.

220Ω or higher resistor will work well with a 5V power supply. A video demonstration and explanation of this circuit is included below, plus written text for those that prefer to read about it.

Main points:

• LED must be inserted in the right direction (forward biased)
• Resistor value must be high enough value to limit current enough to protect the LED (no more than 20mA) and prevent the resistor from overheating. Covered in more detail below.
• An open switch cuts off current flow to the entire circuit. A closed switch lets current flow as is determined by the other series (connected end to end) components and power supply voltage.

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### Video

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#### Important topics to understand:

• Keep current below 20mA for most LEDs, and resistor power dissipation below 1/8W (0.125W) for the commonly rated 1/4W (0.25W) resistors. Covered in more detail below.
• LED must be inserted in the right direction (forward biased) in order to light up. While forward biased, the Anode is connected toward the positive side of the power supply, whereas the cathode is connected towards the negative side of the power supply (usually called ground). Anode is usually the longer lead of the component and the Cathode is the shorter lead if they haven’t been cut. Cathode also commonly has a flat edge along the rim.

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• Resistor value is selected to be high enough to limit current to no more than 20mA to protect the LED. I = V/R (current in amps equals voltage in volts divided by resistance in ohms).
• Resistor also must not overheat. Most are rated at 1/4 watt (0.25W), but should still be limited to not more than 1/8W (0.125W) for extended periods of time, and be given access to room temperature air. P = IV (Power in watts equals current in amps through a component times the voltage in volts across the component)
• Forward biased LEDs typically drop about 2-3V of the power supply voltage from reaching the current limiting resistor. You need to subtract that voltage from the supply voltage in order to get a more accurate calculation of the current that will flow through the series components.

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Brief circuit schematics with short video – List of pages

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