Using multiple IO expanders in Arrays

Using Arduino LEDs and Multiplexing
1

Hi, I'm very new to Arduino so there may seem like an obvious answer to this question but I'm having trouble addressing pins on an IO expander in an array.

I am using multiple MCP23017 -E/SP chips in a cable continuity testing project. I am trying to create an array that lists the pins of these IO expanders however I'm not sure how to call them up.

I have got the chips working and addressed correctly but it seems to be more of a syntax issue I'm having with this particular problem.

#include "Adafruit_MCP23X17.h"

Adafruit_MCP23X17 mcp1;
Adafruit_MCP23X17 mcp2;
Adafruit_MCP23X17 mcp3;
Adafruit_MCP23X17 mcp4;
Adafruit_MCP23X17 mcp5;
Adafruit_MCP23X17 mcp6;
Adafruit_MCP23X17 mcp7;
Adafruit_MCP23X17 mcp8;


const byte pinsCableBegin[]= { mcp1(0), mcp2(3), 4, 5, 6, 7, 8, 9,10 };

void setup() { ...

For example, if I want to reference GPIO pin 3 on mcp2 in my array, I am unsure how to write that into the software. I have put some code above of what I assumed it would be [mcp2(3)] but this obviously doesn't compile and I wondered if someone knew how I should write this so that the array looks at the correct pin.

Any help would be greatly appreciated.

3

just create an array of objects (like already shown) and then address the MCP and pin.

#include <Adafruit_MCP23X17.h>

constexpr uint8_t noOfMcp {8};
Adafruit_MCP23X17 mcp[noOfMcp];

void setup() {
  Serial.begin(115200);
  Serial.println("MCP23xxx array test");

  for (int i = 0; i < noOfMcp; i++) {
    if (!mcp[i].begin_I2C(0x20 + i)) {
      Serial.print(i); Serial.println(" error");
    }
    mcp[i].pinMode(0, OUTPUT);
  }

  mcp[1].pinMode(2, OUTPUT);    // second MCP, third pin
  mcp[1].digitalWrite(2, HIGH); 
}

void loop() {
  for (int i = 0; i < noOfMcp; i++) {
    mcp[i].pinMode(0, HIGH);
  }
  delay(500);
  for (int i = 0; i < noOfMcp; i++) {
    mcp[i].pinMode(0, LOW);
  }
  delay(500);
}
//
4

Thank you for all the help.

I have tried this code but cant quite get it working but I will keep messing around with it in the meantime.

I had an idea which might make this easier as well but just wanted to verify if this is possible.

I am trying to check continuity between all the pins across the 8 IO expanders which is 128 different pins in total

Is it possible to define an imaginary set of pins that correspond to all 128 IO expansion pins for example,

#define 100 mcp1(0)
#define 101 mcp1(1)
#define 102 mcp1(2)
#define 103 mcp1(3)
#define 104 mcp1(4)
#define 105 mcp1(5)
#define 106 mcp1(6)
#define 107 mcp1(7)
#define 108 mcp1(8)
#define 109 mcp1(9)
#define 110 mcp1(10)
#define 111 mcp1(11)
#define 112 mcp1(12)
#define 113 mcp1(13)
#define 114 mcp1(14)
#define 115 mcp1(15)
#define 116 mcp1(16)
#define 117 mcp1(17)
#define 118 mcp2(0)
#define 119 mcp2(1)
#define 120 mcp2(2)
#define 121 mcp2(3)

...

#define 225 mcp8(15)
#define 226 mcp8(16)
#define 227 mcp8(17)


const byte pinsCableBegin[]= { 100, 101, 102, 103, 104, 105,... 227 };

This would make writing the pins into an array much easier as they would all be successive but I just wanted to know if this was possible before wasting my time trying to make it happen?

Thank you again!

5

describe exactly what is not working.

  • What do you see/get?
  • What do you await instead?
  • How does your schematic look like?
  • Post real pictures of your setup so we can see each and every connection.
6

I have tried compiling and running this in the IDE but the serial monitor only returns:

��me���MCP23est
2 error
3 error
4 error
5 error
6 error
7 error
�����

I have attached how the chips are wired with the diagram and I'm obviously just using different addresses for the different chips but I don't really understand what the code is doing.
Pinout1

I do not have a schematic for this I just wish to be able to address the IO expansion pins on the chips in a similar manner to that of the Arduino board pins.

For examples sake you could imagine that I want to run a continuity test of a cable with 2 ends where each connector has 60 pins so I need 120 total IO and I will be using the IO on the expansion boards to do this test.

The cable would have simple end to end connections e.g. pin 1 on connector 1 goes to pin 2 on connector 2 and so on but I just need to be able to call up the IO expansion pins in my array to be able to do this.

7

what code are you using? Obvious it's not my code from #3 because even the first line doesn't fit to my example.

Post your code!
Also state, what other result on Serial you would have expected to get!

8

This is the code I'm using:

#include <Adafruit_MCP23X17.h>

constexpr uint8_t noOfMcp {8};
Adafruit_MCP23X17 mcp[noOfMcp];

void setup() {
  Serial.begin(115200);
  Serial.println("MCP23xxx array test");

  for (int i = 0; i < noOfMcp; i++) {
    if (!mcp[i].begin_I2C(0x20 + i)) {
      Serial.print(i); Serial.println(" error");
    }
    mcp[i].pinMode(0, OUTPUT);
  }

  mcp[1].pinMode(2, OUTPUT);    // second MCP, third pin
  mcp[1].digitalWrite(2, HIGH); 
}

void loop() {
  for (int i = 0; i < noOfMcp; i++) {
    mcp[i].pinMode(0, HIGH);
  }
  delay(500);
  for (int i = 0; i < noOfMcp; i++) {
    mcp[i].pinMode(0, LOW);
  }
  delay(500);
}
//

I believe this is your code and I have tried to run it twice but I just get this on the output:

MCP23xxx arra���gL�#MCP23xxx array test
2 rror
4 error
5 error
6 error
7 error
��me���MCP23est
2 error
3 error
4 error
5 error
6 error
7 error
�����

I was expecting no errors on the Output but I'm not sure what its supposed to be doing.

Regardless, I didn't know if it was possible to do something as I suggested in #4 ?

9

that's why I asked for a schematic and for real pictures.

The sketch tries to start 8 (eight!) ICs - it seems only the first two are working. Hence get for errors for 2 - 7 .

There is no further output in the sketch - don't expect more information on the Serial.

Step 1: let's clarify your hardware.
including why your serial output seems to be incomplete.

10

Thanks for clarifying, it makes alot more sense now.

I only had 2 ICs connected when I ran that test hence the errors detected on the other 6.

I will add the other 6 and retest then get back to you if I still cant integrate it with my circuit.

Thank you again!