Nov 022013
 

Got myself a relay module the other day, as I wanted to use an actuator, and the current supplied from the Arduino itself was not enough to make it work.

This is what I got, http://www.kjell.com/sortiment/el/elektronik/mikrokontroller/arduino/relamodul-for-arduino-p87878.

Here is how I connected the 'Songle SRD-05VDC-SL-C' relay with an actuator to an Arduino.

The pin marked:
'+'  connected to 5V from Arduino
'- ' connected to GND from Arduino
'S' connected to GPIO#2 from Arduino

In the other end connect the middle connector ('Common') to an external voltage source,
in my case 5V, as the actuator was a 5V actuator. The NO ('Normally Open') connector is strapped to one of the actuators input. The NC ('Normally Closed') connector is not used. The other actuator pin is connected to the external power sources GND completing the circuit.

When the GPIO#2 is put high, the external 5V source is fed to the actuator, making it move.
So the only thing you need in your Arduino sketch is 'digitalWrite' of the proper GPIO.
It took me some time to figure the relay out, since I watched some instruction on the internet on how to connect a relay, and all of them used some external diodes and transistors.
But that is not necessary with this one, as it is already mounted on the PCB of the relay module.

ASCII art of the setup:

---------
        |
Arduino |      -----------------
        |      |               |
        |      |     Relay     | 
   5V  --- + --|               |-- NC
        |      |     module    |
   GND --- - --|               |-- Common ---------------- 5V external src
        |      |               | 
GPIO#2 --- S --|               |-- NO -----|
        |      |               |           |       ------- GND external src
        |      |               |           |       |
        |      -----------------           |       |
---------                                  |       |
                                           |       |
                                         --------------
                                         |            |
                                       ==|  Actuator  |=====|
                                         |            |
                                         --------------

Link:
The vendor data sheet of the module, http://www.songle.com/en/pdf/20084141716341001.pdf

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