RobotFuzz

The PCF8574A provides general purpose remote I/O expansion for most microcontroller families via the two-line bidirectional bus (I2C-bus).

The device consists of an 8-bit quasi-bidirectional port and an I2C-bus interface. The PCF8574A has a low current consumption and includes latched outputs with high current drive capability for directly driving LEDs. It also possesses an interrupt line (INT) which can be connected.

Features:

• Operating supply voltage 2.5 to 6 V
• Low standby current consumption of 10 uA maximum
• I2C-bus to parallel port expander
  
  Price £3.49

An Open Source InterFace is a USB to I2C converter.

This interface converts USB signals to the fast (400khz) I2C interface.

With schematics, hardware layouts, and source code, it is the perfect debugging and control device.

Examples:
Controlling PCF8574 I2C to IO interface
Temperature sensing via LM75
Any I2C interface that conforms to I2C specification
Controlling an OpenServo

The OSIF is designed to control the OpenServo servo motor controller, but will serve as a generic USB to I2C interface.