12V Relay Module Project


Materials I plan on using:

  • 5V or 12V 1 Channel relay module
  • 12V DC Dosing Peristaltic Pump
  • Arduino UNO
  • Battery Pack 4x AA
  • Elechouse V3 Voice Recognition module (has microphone)

You have a 12V relay. You have to power it from 12V. Even your pump is underpowered since 4xAA gives you about 6 volts.

Really, you should only have two wires from the Arduino. One ground and one control input to the relay module.

I Googled trying to get hold of the data sheets and got this:
Voice Recognition With Elechouse V3 And Arduino - Arduino Project Hub

Any help there?

Hi, @sammiet03
Welcome to the Forum.

Thanks for all the necessary info and images needed to get your postings off to a good start. :+1:

If you have not already,
Please read the post at the start of any forum , entitled "How to use this Forum".

It will help you use all the facilities of the forum.

Thanks.. Tom... :grinning: :+1: :coffee: :australia:

@ aarg

I have tested both 5 and 12 volt Chinese type relay modules.
I found that only the 5 volt relay modules worked together with my UNOs.

Some 12 volt modules does not "make" supplied with 5 volt as they have 3 pins named Vcc, GND and In.
Giving that Vcc 12 volt forces In to sink 12 volts. A Vcc of 5 volt lights up the LED but the coil doesn't pull.
The single relay module is of that kind. The double relay modules have an option to, as I guess, select high level trigger (preferable using Vcc 12 volt)

What do You think?

Sure, I have several of the dual modules that I intended for model railroad switching. The "red boards" that you show above, appear to have captured the market and are all over Ebay, Bangood, AliExpress and many other places. I can't speak to the single module as I don't have any.

The dual 12V can definitely work with a 5V UNO. The tricky thing is, there is no JVCC jumper on these for separate powering of input and relay power. So far I have not been able to find any schematics online :expressionless: but I found out some things from DMM'ing the board (yes now it's a verb!) and also comparing with this "close approximation":

The difference is, everything that says 5V there, is connected to the "DC+" terminal. The "DC-" terminal is a common ground between the 12V power ground and the Arduino ground. Same as depicted here.

So, to use with the Arduino, you connect DC- to both Arduino GND and to the 12V power supply negative. DC+ goes only to the 12V power supply positive. The jumper should be set to the "High" position, the relay will be switched on when a logic HIGH is presented.

You are correct, when using in a fully 12V system, you could change the jumper to "Low" and then it would have to be fed from a 0-12V source, or else from an open collector or open drain source referenced to ground.

Tip: Maybe you notice that the grounds aren't opto isolated. You can accomplish that by removing the jumper, and running the center pin of the High/Low jumper to processor Vcc or processor ground instead. Then the opto isolator input path is completely isolated from the DC- terminal.

The isolation gained with that mod, isn't sufficient for mains voltage isolation because the PCB layout doesn't support it safely, but it is more than adequate to decouple the low voltage control circuits. If the ground wiring is done thoughtfully, the common ground shouldn't be a problem, though... so a simple GPIO connection to the "in" pins with the processor sharing ground with the 12V supply, would be okay.

It seems to me, the single relay module doesn't have all this flexibility. But in all probability, you should be able to apply 12V to the VCC pin, and 5V logic signals to the IN pin. In this case, the 12V power supply and the processor board should also share a common ground.

Because, the single relay module probably looks like this, again I am just using this for illustration:

Still looking at the single relay module above. Notice that the base drive for the transistor has no connection at all with 5V on the board. Thus a 9V, 12V, 24V board circuit would still look the same, and still accept 5V logic control signals.

Only, everything labelled "5V" in the diagram above would read "9V", "12V", "24V" etc.

So, the only thing (barring other problems) that the OP needs to do, is remove the red jumper between Arduino 5V and the VCC on the relay board, and route the relay VCC to the battery + connection instead.

The other problems mentioned still hold, like powering a 12V relay on a 6V battery pack.

Or move the strap one step. It looks like 3 pins there. I only see a black jumper. Never mind, move it to the other position. What do You say?

  1. Jumper on "high" - input is referenced to ground.
  2. Jumper on "low" - input is referenced to 'DC+'.
  3. Jumper removed - input disabled
  4. Jumper removed, center pin connected with a wire jumper to an off board reference - input is referenced to some off board voltage. Useful application is to connect it to MCU Vcc, then no part of the input circuit connects to anything at all except the opto input LED.

No, but this one - the single relay version of the double - does. :+1:

There you go...

I would like to move that strap to the left and use a positive digital output for activating the relay.

That would be incorrect if you are selecting the "low" setting, since it's on the left. What you want for a positive digital output is the "high" jumper setting. It was the factory default for the ones I bought.

You're perfectly right! Going one more rond with the DMM verifies it!
Hi or Low.... Mixing up things from the diagrams above I got out of sync... Your reply #6

Wouldn't it be great if they provided an actual schematic? :slight_smile:

That would be the day. China, manuals, documentation, after sales support....

One thing though... you should see the questions that buyers or potential buyers ask on the sales sites. Oh boy! Probably makes them wonder if it's worth providing support.

I know. I get some Emails, asked to explain...


You would be better off if you drew your circuit with pen(cil) and paper and used proper symbols, rather than a Fritzy image.

Include your power supply, label components and pin numbers.

Thanks.. Tom... :grinning: :+1: :coffee: :australia:

The relay will be a 5V coil relay, switching 12V.

Tom... :grinning: :+1: :coffee: :australia: