uno powering 2 pots and 1, 8 channel relay.

Projects General Guidance
1

Hello and thank you for reading this!!!

Is it proper design to read two pots at the end of a 15 foot shielded cable and energize a typical 8-channel opticouple modular relay from an USB powered Uno?

The pots are hooked up to +5V, Gnd and analog inputs of the Uno.

The relay is also hooked up to +5V, Gnd and digial outputs of the Uno with independent power for high voltage side.

All are working very well and the pot readings are rock steady.

Thank you!!!

(the diagram is not using the exact module but you might get the idea :slight_smile: )

Untitled Sketch 2_bb.jpg
Untitled Sketch 2_bb.jpg1428×1044 217 KB

2

The maths on USB power is easy.

There is a 500mA fuse inline with the USB supply.
The Uno takes 50mA for itself, so there is 450mA max available.

A 10k lin pot draws 5/10k= 0.5mA, so only 1mA for two.

A relay opto draws 2mA, and the relay coil draws ~75mA...when active.
That means that the fuse will eventually pop when you activate more than five relays.

So it's best to power an 8-relay module with a separate 5volt supply.
That also gives you the option to use opto isolation (not enabled by default).
Leo..

3

house231:
the diagram is not using the exact module but you might get the idea :slight_smile:

Untitled Sketch 2_bb.jpg
Might we? That diagram does not even show a relay shield!

Well now, if it is not the exact module, then it is probably not relevant at all. What is it?

It is a waste of time if answers are given which do not match the actual situation! :astonished:

4

Thank you Wawa for the help. As previously stated the relay is a common 8 channel optoiso module for the Arduino. Sorry, Fritzing did not offer a drawing component for it.

I will power it with a separate source...good call. Not sure how to do that could you send me a link? Thank you so much.

(Someone mistook the word "project guidance" for "missile guidance" in an earlier reply- sorry everyone.)

download shield.jpg

5

If you want opto isolation (possible with a separate relay supply), then.

  1. Remove the jumper, and connect the 5volt relay supply to JD-VCC and ground of the relay module.
  2. Connect relay VCC to Arduino 5volt, and relay inputs to Arduino pins.
  3. Do NOT connect relay ground to Arduino ground. If you do, then you don't have opto isolation.

Random picture of that taken from the net here.
Leo..

6

Wawa:
Random picture of that taken from the net here.

OK, that too!

7

And...
If you don't want these types of relays to activate for during bootup,
then write a HIGH to the pin in setup() before you set the pin to OUTPUT.

digitalWrite (relayPin, HIGH);
pinMode (relayPin, OUTPUT);

Leo..