March 2018
Beginner to intermediate
410 pages
10h 40m
English
Content preview from Mastering Internet of Things
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Connecting an LED
An alternative to working with the alternating current (AC) is to use a low-power direct current (DC) source and an LED to simulate a lamp. You can connect the COM connector to a resistor and an LED, and then to ground (GND) on one end, and the NO directly to the 5V or 3.3V source on the Raspberry Pi on the other end. The size of the resistor is determined by how much current the LED needs to light up, and the voltage source you choose. If the LED needs 20 mA, and you connect it to a 5V source, Ohms Law tells us we need an R = U/I = 5V/0.02A = 250 Ω resistor. The following figure illustrates this:
Connecting a LED
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