Pin connections:
SDA to pin 4 on the analog header
SCL to pin 5 on the analog header
VCC to 5v
GND to GND
I/O pins need pull up resistors to VCC.
Board has A0-A2 with solder pads like (|). connect middle to left (power) for a 1, or right (gnd) for a 0. (see picture shown above)
setting the pins:
Wire.beginTransmission(d);
Wire.send(b); // byte for pins 0-7
Wire.send(b); // byte for pins 8-15
Wire.endTransmission(); // stop transmitting
The board supports id 0-7. Add 32 (0x20) to the id and pass that to beginTransmission. My device id was 0 and I passed 32 to beginTransmission
you have to send an even # of bytes. first is the lower 8 I/O pins. second is for the higher 8 I/O pins.
read is similar. here's quick code
Wire.requestFrom(32, 2); // 2 bytes from device 0
while(Wire.available())
{
char c = Wire.receive();
Serial.print(c, HEX); // print the character
Serial.print(", ");
}
you need to first write 1 to pins you would interested in reading from.

1. You should really do a blank board or one with the non C suffix (5v only v.s. 2.5-5.5 Vcc).
2. I notice 3 unpopulated resistors - what are they for? I don't see a schematic pdf link. Address selection?

Sparkfun - Please retire this product! This is a BAD board design - very difficult to work with on a breadboard. The pin spacing (as noted in comments some 4 years ago!) are incorrect, and the SCL/SDA connections are in a very inconvenient/breadboard unfriendly location. In addition, the board size is such that it covers needed holes on a solderless breadboard.

My suggestion - if you are working on a breadboard is to NOT use this part. Get a 28-pin version from another vendor and an IC socket and you'll be good to go. Not to mention there are better chips from NXP and Microchip.

ARRGH! The board as received on 3/26/2015 has INCORRECT spacing between the left and right set of edge-holes. If I set a digital vernier to .800 and lay it along the holes - there is an OBVIOUS mis-match. Which means common .1 headers soldered in will be spaced wide and not go into a standard breadboard. By eye, it looks like the spacing is about .830. Yet another example of the "Fine QC" our Chinese friends are giving us - and that Sparkfun is sleeping at the switch and not doing a thorough QC on incoming parts!

Now I'll have to go back and check all the BOB's I've recently purchased... Sad.

I bought the Breakout-PCF8575, however I'm not sure how prepare it to interface it with the Arduino, in some datasheets the A0, A1 and A2 are wired to ground; SCL and SDA, I understand are connected to an Arduino port via pull-up resistor, my question is: Do I need to solder the pull-up resistors in your Breakout-PCF8575 in the R1, R2, R3 holes?

Additionally, do I need to make a connection between center pin and the right pin in every A0, A1, A2, if I want to have these pins to ground?

Thank you

Hi,

I need to read/write 16 I2C devices which have the same I2C address (0x68) using only one I2C port in my uC. Is possible to this with this product?

Thank you,

With Interrupt

//All three address pins to ground
#include <Wire.h>
int interruptPin=2;
int i;

void setup()
{
  Wire.begin();        // join i2c bus (address optional for master)
  Serial.begin(9600);  // start serial for output
  pinMode(interruptPin, INPUT);
}

void loop(){
  i=digitalRead(interruptPin);

  if(i==0){
    Wire.requestFrom(32, 2);
    while(Wire.available())    // slave may send less than requested
      { 
        byte c = Wire.read(); // receive a byte as BYTE
        Serial.println(c, BIN); // print the data
      }
      Serial.println(); //Puts a line in serial terminal
    }
}

Can someone please define the difference between the PCF8575 and the PCA9555? What I need is something that will simply give me additional I/O digital pins for my RedBoard. All of these additional I/O will have a bunch of sensors. I'll need to be able to change the address as I am already using SDA and SCL pins. Which version is easiest to work with? Which one has the best tutorials for the total Noob that I am?? Thanks

Does this expander also increase the distance that I2c data will transmit reliably?

It would be nice if more of these breakout boards were designed to mount directly to breadboards just by adding a few header strips. These boards were perpendicular pinouts make for more difficult development.

I am using the PCF8575 breakoutboard to connect 4 mpr121 boards. Without the PCF8575, the mpr121 code worked perfect. (http://code.bildr.org/download/1010.zip) However, I am having trouble to alter my arduino code to read the data when connected to the PCF8575. I guess the problem lies in the part of the code where the pins are adressed. In the original code I used Wire.requestFrom(0x5A,2); However with the PCF8575 board I need to alter the addressing within the code. I had a look at the sample AVR code, but this is rather complicated. Can anyone help me with the adressing of the pins?

Hello!

My only PCF8575 provides between 1.6 and 2.6 volts in output. The power supply is 5 V and have resistors of 10 K between sda / scl and VCC. Any suggestions to solve the problem being?

Best regards.

Wouldn't a simple DIP atmega8 with internal clock do the same job, for $2?

How many analog i/os are there?

Whoa!!! Where did this come from? I thought I would need a mux, and when I could
Save pins? This is going to be useful.

Could you please do a 3.3V version?

I would like to note that the PCA9555N mentioned above has internal pull-up resistors. This chip and the PCA9535 appear to require external pull-up resistors.

Found an alternative
The PCA9555N is a 24 DIP (0.6 wide) - and there are other packages available, and this is a superset of the 8575.

One detail on the spec. sheet for the inexperienced to be aware of: the maximum GND and Vcc currents are 100mA.
To spell it out, this means that although each pin can deliver 25mA, if you really need this much current, you will only be able to run 4 outputs at a time. I got round this limitation with a bit of multiplexing.
Very nice little breakout and very easy to use.
Thank you very much, Tabouli. Your example code was very useful.

so everyone else knows, unfortunately the 0-7 side does not quite line up with the holes on a protoboard. :( shame if you ask me...

You could add in the features that up to 8 boards can be connected to the same bus thanks to the solder jumpers on the right of the board (ADDR mark).
Note for Arduino users : the pinning of power and I2C signals is compatible* with an Arduino board, thus you can plug this breakout board right in the 4 last analog pins of your board without any shield
(* as 'Tod' did with its BlinkM's package, a wonderful idea)

The AVR code example is much more complicated for such a simple device. In modern days, most every AVR developer uses code library for I2C communication, thus a simpler code using AVRlib C lib or Arduino Wire code would be better.
I could write some examples if I had one this breakout board :)