Will I blow everything up??? :)

Other Hardware General Electronics
1

I want to build a simple circuit that will either connect the output pin to the arduino to take some reading OR send 12V into the output pin.

I know normally you use a realy so that you have one input and 2 output (closed or not closed) however can I do the opposite (Having 2 input that goes to 1 input)

In my case, in the first in, I would put the arduino pin, in the second, I would put 12v and then the output would go to the relay.

I think it might work but I fear sending 12v to the arduino...

I made a simple drawing on a postit just so you can understand better

Thanks!

IMG_21582.jpg
IMG_21582.jpg1224×1632 516 KB

2

That looks safe as long as that "output" connection is not an Arudino output pin, and as long as there's nothing greater than 5V (or less than 0V) at that "output" terminal (when not switched to the 12V position). The normally-open and normally-closed contacts of a SPDT switch or relay are never connected together, so as you've shown it, 12V will never be connected to the Arduino's input.

But, there is something screwy looking about your schematic... It might be OK, but what's connected to "output"? An output from "something" going into an Arduino input is fine (as long as you are in the 0-5V range). But with the relay in the other position, it's unusual to connect the output from something to to 12V. For example, you should never connect an Arduino output to 5V or any other power supply, or to ground, or to another output.

Also, you probably don't need the pull-up resistor on the Arduino input. There are pull-ups built-into the Arduino that you can optionally enable.

3

Output to Common of relay, NC to Arduino, NO to 12V.
Make sure you select a relay with "Break Before Make" contacts.

4

Please try to keep your graphics under 800 pixels or so. This one isn't too bad, but it is a pain to have to scroll around trying to look at a schematic.

On the other hand, thank you for posting a schematic.

5

DVDdoug:
Also, you probably don't need the pull-up resistor on the Arduino input. There are pull-ups built-into the Arduino that you can optionally enable.

There are between a few and a few hundred milliseconds while the Arduino is booting that the internal pullup will be off, so external pullups are sometimes necessary.

In this case though, the external pullup can be eliminated if the OP chooses his relay NC and NO contacts wisely.

6

its safe actually,because between that input never connect at the same time

7

You could also use 1N4007 to prevent unwanted current from going to the output pins .