Using an Arduino UNO R3 to create a small motion sensor. I would like to work with some LEDs but I am really confused on what size resistors I would need.
I want to use the Piranha Superflusx LEDs, its states on their website that the
FORWARD VOLTAGE = 3.1v-3.4v
TYPICAL VOLTAGE = 3.4v
TYPICAL CURRENT = 20mA
Knowledge of the UNO is that it works on 5 volts. If I want to use 20 LEDs, what size resistors would I need? and it is my understandings that for each LED I would need 1 of these resistors attached.
Thanks for your assistance
Tony
Any resistor greater than >250Ω would suffice. You’ll just dim you LEDs (since you limit the current) with a bigger resistance.
HINT : Apply Ohm’s law. You know the voltage level and the needed current. You need to find the res value.
The resistor value in Ohms is calculated using the formula
R = (supply_voltage - LED_voltage)/current_in_amperes.
One pin on an UNO can supply only 20 mA safely (so one LED at that current per pin), and the UNO power supply regulator should not be used to power more than a few LEDs, or it could be damaged.