Some Theory Voltage Resistance Current Ohm’s Law Calculating LED Resistor Values

Voltage V Potential difference Energy per unit charge Drives the current between two points in a circuit DC AC

Current I Flow of unit charge per unit time Ampere – Coulombs/second DC AC I Flow of unit charge per unit time Ampere – Coulombs/second

Resistance R, Ω Opposition to the flow of current Based on properties of the material Conductor vs. Insulator

Ohm’s Law Relates voltage, current and resistance I = V / R V = I * R Units are important – amperes, ohms, volts Not milliamps, and millivolts

Calculating LED Resistor Values LED Voltage and Current from data sheet Typically ~ 1.7V Typically ~ 20mA Know supply voltage – for example 5V Resistor needs to take the extra voltage 5 – 1.7 = 3.3 V Ohm’s Law – R = V/I = 3.3V/0.02A = 165Ω