PCF8574 I2C IO Expander

Do you have too few IO pins, but do you have an I2C bus at your disposal? Then you can use this module to create more (standard) pins.
De PCF8574 works on both 3.3V and 5V. (output equal to input voltage)

Specifications:

• Voltage: 2.5 - 6V DC
• Jumpers present to set I2C address
• 8 extra pins per module
• Pin can be used as input and output
• Pull-up resistors for I2C bus already present
• Possible to link multiple modules together for more pins (up to 8 modules*)
• Chip:  PCF8574(T) or PCF8574A(T) ("A" version has a different I2C address!)

See the datasheet for more information: PCF8574/PCF8574A

Check this page for the library and manual for Arduino: A class for PCF8574

Note: High output signals that will draw 10μA or higher require an external pull-up resistor. Low output signals do not require a resistor and can provide 25mA. See chapters 10.1 and 13 in the datasheet for further details.

* Note: When using 3 modules or more the I2C pull-up resistance will be too low (lower than 333Ω). This probably causes the I2C port of the microcontroller to be loaded too much. In that case we recommend to remove the I2C pull-up resistors on modules so you have a maximum of 3 modules that have pull-up resistors. You can recognise these pull-up resistors by their code marking 102 or 1001.