# Calculations

## LED Formula

### LED Spec:
2.8v (forward voltage)
20ma (current)

Vsupply = 5v (Pi Power)
Vf = 2.8v (Led Volts)
R = resistor value
If = desired current

Vr = Vsupply - Vf
R = Vr / If

Vr = 5V - 2.8V = 2.2V
R = 2.2V / 20mA = 110 ohms
 
Make sure to add some play room, we use a 120 omhs resistor