Question 1

Why does an LED need a resistor?

Accepted Answer

LEDs do not have built-in current limiting, so connecting one directly to a power source will cause excessive current to flow and damage it. A series resistor limits the current to a safe level, allowing the LED to operate properly.

Question 2

What is the formula for calculating the LED resistor value?

Accepted Answer

R = (Vs - Vf x n) / If, where Vs is supply voltage, Vf is forward voltage per LED, n is the number of series LEDs, and If is forward current. For example, with a 5V supply and a red LED (2.0V/20mA), R = (5 - 2.0) / 0.02 = 150 ohms.

Question 3

What is the E24 series?

Accepted Answer

The E24 series is a standard set of preferred resistance values that divides the range 1 to 10 into 24 steps (1.0, 1.1, 1.2, 1.3, 1.5, ...). Commercial resistors are manufactured in these values, so it is common practice to select the nearest E24 value above the calculated resistance.

Question 4

How do I choose the wattage rating for the resistor?

Accepted Answer

The power dissipated by the resistor is P = If squared x R. It is generally safe to use a resistor rated at least double the dissipated power. For example, if the dissipation is 60 mW, choose a 1/8W (125 mW) or larger resistor. This tool warns when dissipation exceeds 250 mW.

Question 5

Is my data sent to a server?

Accepted Answer

No, all calculations are performed entirely within your browser. Your data is never sent to any external server.

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