Iterating an array of relays

Question

Bear with me as I'm fairly adept at C# but I am having a problem understanding how to get an array iterated.

I am writing a program to test relay boards, it will eventually have an input mechanism to select the number of relays on the board. For now, i just need to get an array iterated to move on with the code.

The biggest relay board I've seen has 16 relays, so....

#define Relay1  2  // Arduino Digital I/O pin numbers for UNO R3
#define Relay2  3
#define Relay3  4
#define Relay4  5
#define Relay5  7  
#define Relay6  8
#define Relay7  9
#define Relay8  10
#define Relay9  11  
#define Relay10  12
#define Relay11  13
#define Relay12  A0
#define Relay13  A1 
#define Relay14  A2
#define Relay15  A3
#define Relay16  A4

int relays[]{ Relay1,Relay2,Relay3,Relay4,
    Relay5,Relay6,Relay7,Relay8 };
int maxRelayCount = 8;
char rx_byte = 0;

void setup()   //Initializes all variables and settings
{
  Serial.begin(9600);
 // create an input for the amount of relays on the board
//hardcoded for now

//Set pins to OFF & declare pins as OUTPUTS
 for(int i = 0; i < maxRelayCount; i++)
 {
   digitalWrite(relays[i], RELAY_OFF);
   pinMode(relays[i], OUTPUT);
   //How to convert i to a string in c++?
   //Serial.print("Relay " +[i] + " set HIGH and as OUTPUTS");
 }

 //Check that all relays are inactive at Reset
 delay(4000); 

}

So there are two issues. If I remove the loop and just hard code 8 times to set HIGH and OUTPUT it works fine, but the loop does not and won't upload to the Arduino, thus the reason I believe it is wrong. Secondary question is how to convert the counter i to a string to concatenate the message

Why not break the print statement into three parts; Serial.print("Relay["); Serial.print(i); Serial.print("] set HIGH and OUTPUT"); — Mikael Patel
– Mikael Patel, Commented Apr 2, 2016 at 18:27

Community · Accepted Answer · 2017-04-13 12:50:09Z

As noted earlier, RELAY_OFF needs a defined value.

Note, rather than using clumsy list of #define statements to define a bunch of integer constants, you can use C's enum declaration to define them, as shown in the following sketch, which produces the output

Relay 1 should be OFF
Relay 2 should be OFF
Relay 3 should be OFF
Relay 4 should be OFF
Relay 5 should be OFF
Relay 6 should be OFF
Relay 7 should be OFF
Relay 8 should be OFF

when it is run.

#include <Streaming.h>

// Arduino Digital I/O pin numbers for UNO R3
enum { Relay1=2, Relay2=3, Relay3=4, Relay4=5, Relay5=7, Relay6=8,
       Relay7=9,   Relay8=10,  Relay9=11,  Relay10=12,  Relay11=13,
       Relay12=A0, Relay13=A1, Relay14=A2, Relay15=A3,  Relay16=A4};

int relays[] = {Relay1,Relay2,Relay3,Relay4,Relay5,Relay6,Relay7,Relay8};
// Number of relays in the array
enum { maxRelayCount = sizeof relays / sizeof relays[0] };
enum { RELAY_OFF = HIGH };  // Set LOW or HIGH as appropriate
char rx_byte = 0;

void setup() {          // Initialize variables and settings
  Serial.begin(9600);
  //Set pins to OFF & declare pins as OUTPUTS
  for(int i = 0; i < maxRelayCount; ++i) {
    digitalWrite(relays[i], RELAY_OFF);
    pinMode(relays[i], OUTPUT);
    // Serial.print("Relay " +[i] + " set HIGH and as OUTPUTS");
    Serial << "Relay " << i+1 << " should be OFF" << endl;
  }

 // Check that all relays are inactive at Reset
 delay(4000);
}

void loop() {}

Note, the Streaming.h library adds some “syntactic sugar” to Arduino C. At compile time it converts C++-like << Serial stream operators to Serial.print statements, without increasing code size. You can install it by unzipping Streaming5.zip from arduiniana.org in your sketchbook/libraries directory.

I didn't put the RELAY_ON and RELAY_OFF defines in the question, but I like the usage of enum and the streaming library — dinotom
– dinotom, Commented Apr 2, 2016 at 19:39

Majenko · Accepted Answer · 2016-04-02 18:18:14Z

2

the loop does not and won't upload to the Arduino

Most likely because RELAY_OFF has never been defined anywhere. Change that to HIGH (if that is what your relays need to turn off), or define it somewhere.

Also there is no loop() function - is that just you being economical with the paste?

Secondary question is how to convert the counter i to a string to concatenate the message.

Simple: don't. There's no need.

Serial.print("Relay ");
Serial.print(i);
Serial.println(" set HIGH and as OUTPUT");

answered Apr 2, 2016 at 18:18

Majenko

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