Using D18/SDA & D19/SCL in lieu of A4 & A5

Official Hardware UNO Family UNO R3
21

Are IO pins designed to feed electrical load?

22

As opposed to a load of hay? :grinning_face: Yes they are designed to feed an electrical load. They are not generally considered to be used as a power supply although they can be under the appropriate conditions. Since they are essentially a switch to Vcc or Gnd if you use them that way they can power e.g. sensors with very low current requirements and wide supply voltage range.

Since OP seems determined to use them as a torture test for their board, that could be considered not appropriate.

23

No. See post #20

24

Can a LED be cosidered an electric load?

25

Anything that presents an impedance to the source and consumes electrical energy is an electrical load.

26

An IO pin never switches to Vcc; it switches to VOH which could be equal to Vcc. Similarly, it may swicth to 0V and NOT GND-pin (as 0.9 V is max) which is equal to GND.

I digital electronics, we have

GND 
Logic Low 
Logic High
Vcc
27

The 75HC595, when connected to an I/O pin, draws current, so it acts as an electrical load — correct? If that would be correct, then there would be no distinction between the definitions of Electrical and Electronic Engineering.

28

When we talk about semiconductor switches, we talk about them switching to some source or sink while realizing they are not mechanical switches.

If you wanted to power something from an I/O port you would attach one end of the load to either Vcc or Gnd and switch the other end with the I/O port. Just like if you used a discrete semiconductor switch.

30

If you are driving an LED from an I/O pin are you driving a load?

You edited your comment while I was typing mine hence the appropriate response. After I saw your final response I edited mine to match yours. Unfortunately it wasn't within the time allowed for a change without being recorded as an edit.

31

Very difficult to answer as an LED draws considerable amount of current compared to a logic gate.

32

@GolamMostafa @EmilyJane
Come on you lovely people, be nice!
I've done a bit of tidying up.

Thank you :slight_smile:

33

Thank you. I was abrupt.

34

Thank you for doing a good job.

35

Could that be "loading" down the I/O pin?

36

Yes but it's a constant load. What if the load varies like a motor?