Powering 12 V 8 Channel Relay Module

Other Hardware General Electronics
1

Hi,

I'm pretty familiar with microcontrollers, but I just got new 12 V 8 channel relay module and I'm not sure how to connect it. Maybe some of you know this model and could help me with corrrect wiring.

Take a look at the attachments.

I guess VCC and GND are just 12 V and ground, but I wonder what to do with COM in this case?
Then, to operate it I'd use arduino digital pin to trigger one of IN pins.

Hardware:
12 V power supply for:

  • Arduino Mega 2560 R3
  • 8 Channel Relay Module (SRD-12VDC-SL-C)

I'd like to trigger one of relays using digial pin 11 between HIGH and LOW.

Software:

void setup()
{
  pinMode(11, OUTPUT);
}

void loop()
{
  digitalWrite(11, HIGH);
  delay(5000);
  digitalWrite(11, LOW);
  delay(5000);
}

IMG_20210213_114257.jpg
IMG_20210213_114257.jpg2400×3200 1.83 MB

IMG_20210213_114257.jpg
IMG_20210213_114257.jpg2400×3200 1.83 MB

2

OK, that photo is sufficiently detailed to allow me to see to what the "COM" connects, and it connects to the anode of an indicator LED.

So you connect COM to the 5 V on your Arduino and you pull an "IN" LOW to activate a relay.

While the relay module (that is, the relays themselves) operates on 12 V, You will also need a 5 V power supply for your Mega 2560 if you propose to connect other devices to it that require 5 V.

Similar circuit, ignore the "Jumper".

3

Thanks for reply!

I tried to show this area well hence the weird angle of the photo.

I assume it's ok to use 5 V available on Arduino to power COM port on relay board + couple of DS18B20 sensors? They draw very little current.

4

Well, you may get away with it, but the on-board regulator of the Mega 2560/ UNO/ Nano/ Leonardo etc. has negligible heatsinking and is really little more than a decoration. :astonished:

A switchmode "buck" converter powering the "5V" pin (except when the USB port is connected to a PC) would be more reliable.

5

Thanks once again.

Do you mean step-down converter? Could you post an example of such just to be sure? I guess it's something like LM2596, etc.?

6

Indeed, but you want a ready-built module.

Aliexpress item

7

Thank you. That's what I thought about.

8

Looks like you have the 12V version of this board where you would connect a "Relay 12V Power Supply". It would be good to take advantage of the opto-isolation feature, but they show a connection scheme that shorts out this feature. Specifically, its the GND connection to Arduino that cripples opto-isolation.

I wonder if the relay board would work fine and provide full opto-isolation if the Arduino GND connection were removed.

The opto isolators are there on the board (the 4-pin ICs) - its a shame not to utilize them.

800×543 55 KB

9

OK, so that illustration is ignorant nonsense - for whatever reason. :roll_eyes:

No wonder they discontinued the item! :sunglasses:

10

The only connections to Arduino should be:
A wire to COM and a wire from each "In#" to an output pin, if wired for "LOW true" COM to be connected to Arduino Vcc, else to Arduino GND. DO NOT connect BOTH Arduino Vcc AND GND to the relay board!

11

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