Design an LED Circuit

Calculate the LED Resistor Value

After gathering your hardware, build an LED circuit that simply lights up using the 5V supply from the Jetson without any control. This requires a simple series circuit with an LED and resistor. In a simple series circuit, the voltages add and the current is the same everywhere in the loop.

LED Voltage and Current

The datasheet for a particular LED provides information about how much current and voltage should go through and across the LED. For example, the data sheet for a 5mm yellow LED indicates a forward current is 20mA, and the forward voltage is between 1.8V and 2.2V, or an average of 2.0V. To design the circuit then, we assume optimal values for the LED of

I_{LED}=20mA

V_{LED}=2V

What else does this tell us? Since this is a series circuit and all current is the same in the loop, this tells us not only the target current for the LED, but the resistor as well.

I_{R} =20mA

Kirchhoff's Voltage Law (KVL) requires that the supplied voltage in a loop equal the voltage drop across the components. Since the components are in series and summed, the voltage drop across the resistor can be calculated.

V_{R} = 5V - 2V = 3V

Ohm’s Law

By Ohm’s Law, V=IR. To calculate the resistor value, R=V/I:

V_{R} =3V/20mA = 150\Omega