PCF8574, I2C and the mbed

A user on the mbed site asked for some help getting an I2C application to work with the mbed.

He's using a PCF8574 port expander which is driven from one of the mbed's I2C busses, which is on pins p9 and p10.

He wants to turn a LED on when a button is pushed. The button is connected to P4 on the port expander; the LED is attached to pin 5.

Here's the breadboarded circuit under manual test :)

And here's the code:

#include "mbed.h"
#include "PCF8574.h"

PCF8574 io(p9,p10,0x40);

int main() {
    while(1) {
        if ((io.read() & 0x20) == 0) {


  1. Thanks for sharing this :)

    Just what i needed to get another 6 GPIO's !




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