We need to know the voltage around the LED. Usually, a 5 mm LED needs 15 - 30 mA to be in
good lighting. After knowing the forward voltage for the LED, it is easy to calculate the resistance.
To measure the forward voltage we connect a high value resistor, so we ensure that a low current
will pass through the LED.
8.5.1 Example
Calculate the resistance in the following circuit for a red LED to make it consume around 20 mA.
Now, we need to build the circuit with a red LED, and we will use a high resistor, in our case, we
will use a 2.2 kΩ resistor and measure the forward voltage using the multimeter.
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Mastering the Art of Measurement (DM401B Smart Digital Multimeter) r.01 www.plusivo.com
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