Hello everyone! I plan to use my Uno board to illuminate 8 LEDs. Will the LEDs surpass the output limits of the board?
So I want to buy eight 6000MCD white LEDs rated at 3.2V @ 20mA. Each will be connected to pins 1-8 via a 100ohm resistor (1/8W or higher). Can the Arduino board can power all this? I do not have a relay shield.
Thanks very much in advance!
Well, that's 160mA, the 328P-PU can support 200mA, as long as the current is spread across the ports appropriately:
3. Although each I/O port can source more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state conditions (non-transient), the following must be observed:
ATmega48A/PA/88A/PA/168A/PA/328/P:
1] The sum of all IOH, for ports C0 - C5, D0- D4, ADC7, RESET should not exceed 150mA.
2] The sum of all IOH, for ports B0 - B5, D5 - D7, ADC6, XTAL1, XTAL2 should not exceed 150mA.
If IIOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current greater than the listed test condition.
4. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state conditions (non-transient), the following must be observed:
ATmega48A/PA/88A/PA/168A/PA/328/P:
1] The sum of all IOL, for ports C0 - C5, ADC7, ADC6 should not exceed 100mA.
2] The sum of all IOL, for ports B0 - B5, D5 - D7, XTAL1, XTAL2 should not exceed 100mA.
3] The sum of all IOL, for ports D0 - D4, RESET should not exceed 100mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater than the listed test condition.
Thank you so much! It's working really well right now.
Also, how much mA will be taken up by all 8 corresponding 100ohm resistors? If I connect each LED to pins 1-8 still with 100ohm resistors for each LED, will the Uno board still be able to power the circuit?
Work out the current for one. That will be (5V - Vf)/ R
Where Vf is the forward voltage drop of the LED and R is your resistor value. Then multiply by 8 and distribution them like CrossRoads told you.
Thanks so much for your answer! Found out that the entire circuit would be around 300mA and thankfully I only ran my circuit once, otherwise I would probably overload and damage the board. As CrossRoads said, the Atmega328P-PU microcontroller chip can only handle a total of 200mA.
I stopped using my circuit and decided to just power the lighting system with AA batteries instead and without the Uno. Thanks for your help.
As CrossRoads said, the Atmega328P-PU microcontroller chip can only handle a total of 200mA.
Well one train of thought says there are two +5V pins so that limit is pushed to 400mA.
However that is just for sourcing current, you can get another 200mA of current by sinking. To light an LED by sinking wire the resistor to +5, the LED to the resistor and the other end of the LED to the output pin. Then a logic LOW will turn on the LED.
You still have to distribute the sourcing and sinking port limits correctly though.