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

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

3. Current I Flow of unit charge per unit time Ampere – Coulombs/secondDC AC I
Flow of unit charge per unit time
Ampere – Coulombs/second

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

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

6. 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