write to PCF8575


i am strugling writing to a PCF8575 board.

I want to set an individual pin high ot low just like the pins that are on the espboard.
Setting that pin must not influence the other pins.

All the examples that i find are not working or setting a range of pins in one time.

what i want is like this:

int Fan = 27;//Fan relay pin

pinMode(Fan, OUTPUT);
digitalWrite(Fan, HIGH);

on an event:

digitalWrite(Fan, !digitalRead(Fan)); //togle

it is working whit the pins on board but not with the pins on the PCF8575 board

Can some one point me the right direction ?

Have you got the I2C interface to the I/O expansion board?


i use the example program to test
it is reading and writing only not the way i want it.

I can only send all the pins in one time and not individual