Switching 5 relays via Google Home, IFTTT & Particle


Hi thanks for that, yes I missed the comma.

It now works!! So thank you so much for your help. I clearly need to learn more to expand function and usability. Where to start!?


Hi, Thanks for the guidance, as a very unskilled tinkerer it would be good to learn best practice. Can you elaborate a little (or a lot in my case)? In relation to the code above. Would be nice to have a Switch All command/option too.


That should be easy, e.g. by using the 0 for all relays. Unless there is a “all” command which would then need to be treated that way.


Maybe not best practice :see_no_evil:, but on the way to it :wink: might need more iterations to get there, but tha main expected issues with erronous input data should be caught this way.

const int relayCount = 5;

int setRelay(const char* args)
  char msg[64];
  char relayState[5];
  int  relayNumber;
  int  r0           = 0;
  int  rX           = relayCount;
  bool relayOn      = false;

  switch (sscanf(args, "%d,%4s", &relayNumber, relayState))
    case 2: // all 2 arguments parsed
      relayOn = (strcmp(relayState, "on") == 0);

    case 1: // only 1 argument parsed
      if (0 == relayNumber)
        ; // do nothing, initial values are set to controll ALL relays
      else if (0 < relayNumber && relayNumber <= relayCount) 
        r0 = rX = (relayNumber-1);
        break; // relay number disallowed, bail out

      for (int i = r0; i < rX; i++)
        pinMode(relay[i], OUTPUT); // set as output
        digitalWrite(relay[i], relayOn);

      relayNumber = -1; // no valid relay number provided

  // ------- optional -------
  snprintf(msg, sizeof(msg), "%s -> r[%d] state: %s", args, relayNumber, relayOn ? "ON" : "OFF");
  Particle.publish("log", msg, PRIVATE); 
  // ------------------------

  return relayNumber*100 +  relayOn;


Well done. The mighty @ScruffR strikes again.


OK I am a bit stuck, I added in the pin assignments for the each relay at the top as

int relay[5] = {SDA,SCL,D0,D1,D2};

But should something like

Particle.function("setRelay", setRelay);

be in there? I ask because in IFTTT asks for the call function which is unavailable but {{NumberField}} {{TextField}} show as input (Function Input). Particle console is not picking up anything.


For one, I’d not use SDA & SCL but rather the pin labels printed on the board.
Using any other labels (like you did) will cover the fact that SDA & SCL are also used otherwise (i.e. SDA = D0 & SCL = D1)

In where?
I only rewrote setRelay() all the other functions @nrobinson2000 has provided you with are to be taken the same.


Yes, thanks I am aware of that, its just I have an old set up that is wired that way that I am using for testing. I will look again at integrating the two blocks of code to get this working. Thanks again.


So you have a setup that connects two relays to one pin - twice?

  • relay[0] … D0 (SDA)
  • relay[1] … D1 (SCL)
  • relay[2] … D0
  • relay[3] … D1
  • relay[4] … D2


@MettaUK are you still running this on a Raspberry Pi? Which 5 pins do you want to use?


:flushed: @nrobinson2000, I totally missed that :flushed:

In that case, the point I made about the pins is mute :see_no_evil:


@MettaUK I’m trying to do the same project as you did, where did you put the comma ?
I’m using your code posted above , the logs from Particle console are okay i think, ex 1 off , 5 off but the gpio pins are not changing their state. All of them (D4,D5,D6,D7,D8) are remaining HIGH regardless of the input.
Any idea why is this happening?


The comma goes between NumberField and TextField.

You can see in the original picture: