I2C Ping/Check connected devices

Projects Programming
1

Hi I am using the Ports and PortsSHT21 Libraries to use SHT21 sensors on a project as well as the standard "hard" I2C with SHT2x Library. I need to be able to check if the sensors are actually connected. Is there any way to do this?
I am hoping for a relatively simple way to do something like ping the sensors to see if they are present.

Here are the libraries I am using.

Thanks

2

The SHT21 sensor has a fixed address of 0x40, so you can simply send a command to the sensor and if it replies it's connected. I'd use the "Read User Register" command (0xE7) for that, by default you should get at least a 1 in bit 1.

3

Thanks, That works for the one on the 'hard' i2c but what about the 7 others I have running on soft ports?

4

way over my head but i see a lot of SHT21 going on!

5

Why should there be any difference on the soft ports? If the soft ports work, you can send commands to the device and get a response if the device is there, no response if the device is absent.

I don't know how well the Ports library works, I found at least some strange code:

    delayMicroseconds(2);
    digiWrite2(x);
    delayMicroseconds(5);

delayMicroseconds() has a minimal value of 4 because the call and the initialization of the variables need about 4 microseconds at least. It probably works but it's a sign that other problems may exist too.

6

Hi,
I do realise that this library is not perfect, however in practice it works and quite reliably, I don't have the programming skills to actually fix it. I haven't quite worked out how to just send commands and receive replies over the soft i2c channels yet.

Many thanks

7

Nick Gamon (one of the moderators) has written an I2C scanner on his site at http://www.gammon.com.au/forum/?id=10896

he says "If you have a device you aren't sure of the slave address of, you can run the sketch below. It tries every possible address (from 1 to 119) and if a device responds, prints that address."

// I2C Scanner
// Written by Nick Gammon
// Date: 20th April 2011

#include <Wire.h>

void setup() {
  Serial.begin (115200);
  Serial.println ();
  Serial.println ("I2C scanner. Scanning ...");
  byte count = 0;
  
  Wire.begin();
  for (byte i = 1; i < 120; i++)
  {
    Wire.beginTransmission (i);
    if (Wire.endTransmission () == 0)
      {
      Serial.print ("Found address: ");
      Serial.print (i, DEC);
      Serial.print (" (0x");
      Serial.print (i, HEX);
      Serial.println (")");
      count++;
      delay (1);  // maybe unneeded?
      } // end of good response
  } // end of for loop
  Serial.println ("Done.");
  Serial.print ("Found ");
  Serial.print (count, DEC);
  Serial.println (" device(s).");
}  // end of setup

void loop() {}
8

Thanks Lemming good find.
My only question now is ow to implement that on all 7 soft ports.

9

Beyond me but maybe you should ping Nick as he is the moderator for this forum.

10

Hi, thanks
I have PM'd him, hopefully he should reply soon.

11

Ok so I ran the code and the scan picks up 9 devices,

I2C scanner. Scanning ...
Found address: 64 (0x40)
Found address: 80 (0x50)
Found address: 81 (0x51)
Found address: 82 (0x52)
Found address: 83 (0x53)
Found address: 84 (0x54)
Found address: 85 (0x55)
Found address: 86 (0x56)
Found address: 87 (0x57)
Done.
Found 9 device(s).

The first one is the hard I2C channel SHT21 and then the second one is an I2C EEPROM chip, then I am guessing the other 7 detected are my soft channels. but only 3 of the channels have devices connected.