PCF8574 IO Expander Board - Tutorial/example requested

[dome]

I’m looking to start a project (an internet-connected, openHAB enabled busy board for my kids!) and my plans involve significantly more IO pins than the photon has.

I have been looking at the PCF8574 as a means to connect a bunch of switches to the setup. I have found some Arduino tutorials for the IC but nothing specific to the Particle platform.

I have seen some discussion on the Particle forum so I believe it is compatible, but none of the examples I found included any code.

Does anyone know of either an Arduino-based PCF8574 tutorial that’s code compatible with Particle, or have a Particle-based PCF8574 project they’d be willing to share? I think I could get it off the ground if I could see some basic coding examples.

pcf8574.pdf

[ScruffR]

Have you got a link to the Arduino library to look at?
But with enhanced Arduino compatibility of system 0.6.2 you could just try to build the code and see if it compiles.

[cermak]

SparkFun has a retired break out board that you might be able to base some code from (firmware/library) for the chip you specify.

sparkfun/I2C_Expander_Breakout-PCF8575

Otherwise, there are some other alternatives with active (user contributed) libraries:

Adafruit_MCP23017 1.0.2 136 Adafruit_MCP23017 I2C expander library adapted for Spark
MCP23008-I2C 0.0.10 47 A version of Ladyada's MCP23008 8-bit I2C IO Expander library, ported for use on Spark Core.
mcp23s17 0.2.0 23 A C++ wrapper for the Microchip MCP23S17.
MCP23S17_bd78 0.0.1 14 Library for MCP23S17 SPI IO expander. Originally written for Arduino by Cort Buffington & Keith Neufeld.
Adafruit_MCP23008 1.0.6 5 Adafruit_MCP23008 I2C expander library adapted for Particle IDE
MCP23008-RK 0.0.1 0 Particle driver for 8-port I2C GPIO Expander MCP23008

Several based on the MCP23* series. AdaFruit has a breakout board:

MCP23008 - i2c 8 input/output port expander

The update product that replaced the retired product above is the SX1509 and there is a library within Particle for that board.

SparkFunSX1509 2.0.2 7 Arduino library and hardware files for the SX1509 IO Expander Breakout board.

SparkFun 16 Output I/O Expander Breakout - SX1509 - BOB-13601 - SparkFun...

Some alternative options with libraries available in the Particle library.

[rickkas7]

I use the MCP23008 I2C GPIO expander in my I2C tutorial, see the “GPIO Expanders” section. There’s a link to the Particle library there as well.

rickkas7/particle-i2c-tutorial

[dome]

Thanks for the suggestions! I’ve had a busy weekend and haven’t had a chance to dig in. I originally wanted to go with the PCF8574 because I already had a few of them, but it’s looking like it might be easier to just run with the MCP230xx.

[dome]

@ScruffR I tried a few Arduino tutorials for the PFC8574 but couldn’t get any of them to compile… probably problems with the libraries; I decided to go the MCP230xxx route.

@rickkas7 Someday, I’ll learn to check the code before I buy the parts… I ended up buying some MCP23017 chips instead of the MCP23008. I liked the idea of having more pins per chip and didn’t realize it wasn’t supported by your library.

I will order some MCP23008… but before I do, is it possible to modify the library to work with the MCP23017? I tried connecting it to the Photon and just using pins 0-7 but that approach didn’t work. I haven’t had a chance to dig in beyond that.

[dome]

@rickkas7 Disregard, I got the MCP23017 working with an Adafruit library I found in the IDE. Not sure how I missed it the first time… Thanks for the tutorial; even though I used a different library it’s the best explanation I’ve ever seen for using i2c in a variety of ways!

Now the fun can begin in earnest!

[rickkas7]

I did make a MCP23017-RK library that has the same API as the MCP23008-RK but has support for all 16 GPIO pins.

rickkas7/MCP23017-RK

There’s no reason to switch if you have it working with the Adafruit library, just providing the link in case someone finds this post through search.

[dome]

@rickkas7 This is great… thanks for your efforts.

One quick question - I’m looking at hooking up several MCP23017 chips, along with some PCA9685 PWM expanders. Should I use pullup resistors near every device, or just one set close to the Particle?

[rickkas7]

One pull-up resistor (2.2K to 10K) on each of SDA and SCL, ideally near the Photon/Electron, though you can put it anywhere.

But only one set, not one per MCP230xx.

[dome]

@rickkas7 Sounds good. Thanks for the clarification. I’m developing a breakout board for the MCP23017 and wanted to get this clear.

[dome]

I’m making great progress, though some may say I’m going a bit overboard.

[dome]

I’m working on adding more control inputs to my setup but I’m struggling to add more than one MCP23008 or MCP23017 to my Photon. I can’t find an example that references how to define addresses manually; what’s the right way to do that?

[peekay123]

@dome, there are 3 hardware address select lines (A0, A1, A2) for setting the I2C address. For example the MCP2308 datasheet says:

The four most significant bits of the slave address are fixed (0100 for MCP23008) and the remaining three bits are user-defined hardware address bits (pins A2, A1 and A0).

[dome]

@peekay123,

Thanks, though I should have been more clear. I’ve already set the device to address 0x41 in hardware, but I can’t figure out how to define this in software. Every code example I find (for any library) just uses a single chip with the default address.

Edit: not that it matters, but the address I set is 0x21.

[rickkas7]

My libraries support multiple devices/addresses:

MCP23008-RK
MCP23017-RK

They’re in the community libraries as well, but the documentation is at the links above.

[dome]

Thanks, I didn’t find the github pages on my checks. That’s exactly what I needed!

[EulerTourist]

I had success with this library:
https://forum.hobbycomponents.com/viewtopic.php?t=2190

#include "HCPCF8574.h"

HCPCF8574 pcf8574(0x20);

void setup() {
  Serial.begin(9600);
  Serial.println("Vers003");
  pcf8574.init();
  delay(100);

  for(uint8_t i=0; i<8; i++){
    pcf8574.pinMode(i, OUTPUT);
  }

  delay(100);

  Serial.println("Load each pin HIGH and read each");
  for(uint8_t i=0; i<8; i++){
    pcf8574.pinWrite(i, HIGH);
  }

  delay(100);

  for(uint8_t i=0; i<8; i++){
    Serial.printlnf("%i:%i", i, pcf8574.pinRead(i));
  }

  Serial.println("Load each pin LOW and read each");
  for(uint8_t i=0; i<8; i++){
    pcf8574.pinWrite(i, LOW);
  }

  delay(100);

  for(uint8_t i=0; i<8; i++){
    Serial.printlnf("%i:%i", i, pcf8574.pinRead(i));
  }

  Serial.println("Write port with 0x55 then read port");
  pcf8574.portWrite(0b01010101);
  delay(100);
  int pw1 = pcf8574.portRead();
  Serial.printlnf("%#4x",pw1);

  Serial.println("Write port with 0xAA then read port");
  pcf8574.portWrite(pw1<<1);
  delay(100);
  int pw2 = pcf8574.portRead();
  Serial.printlnf("%#4x",pw2);
}

void loop() {}

Output: