Connect a PCF8574 expander to an LPC1768

This 8-bit input/output (I/O) expander for the two-line bidirectional bus (I2C) is designed for 2.5-V to 6-V VCC operation.

This is the module I used

The PCF8574 device provides general-purpose remote I/O expansion for most microcontroller families by way of the I2C interface [serial clock (SCL), serial data (SDA)].

The device features an 8-bit quasi-bidirectional I/O port (P0–P7), including latched outputs with high-current drive capability for directly driving LEDs. Each quasi-bidirectional I/O can be used as an input or output without the use of a data-direction control signal. At power on, the I/Os are high. In this mode, only a current source to VCC is active.


Low Standby-Current Consumption of 10 µA Max
I2C to Parallel-Port Expander
Open-Drain Interrupt Output
Compatible With Most Microcontrollers
Latched Outputs With High-Current Drive
Capability for Directly Driving LEDs


Parts List

Label Part Type Properties
LED1 Red (633nm) LED package 5 mm [THT]; leg yes; color Red (633nm)
LED2 Red (633nm) LED package 5 mm [THT]; leg yes; color Red (633nm)
LED3 Red (633nm) LED package 5 mm [THT]; leg yes; color Red (633nm)
LED4 Red (633nm) LED package 5 mm [THT]; leg yes; color Red (633nm)
MBED1 mbed 1768 variant mbed; processor NXP/ARM Cortex
R1 220Ω Resistor
R2 220Ω Resistor
R3 220Ω Resistor
R4 220Ω Resistor
U1 PCF8574 package DIP16 [THT]; type PCF8574


This example schematic shows only 4 resistor and LED pairs, I used 8 pairs for testing

mbed and pcf8574
mbed and pcf8574


This uses this Mbed library –

#include "mbed.h"
#include "PCF8574.h"
PCF8574 io(p9,p10,0x40);
int main()


You should the LED’s flashing on and off


PCF8574 IO Expansion Board I/O Expander I2C-Bus Development board