I2C Interfaced with NXT

The goal of the project is to provide 8 digital I/O ports with the NXT by using a simple I2C chip with either binary input or output on each one of these 8 ports.

The I2C serial digital protocol is supported by the sensor ports on the NXT and the inputs can either be ON or OFF. Touch sensor-like switches can be used for the input ports while the output ports can drive LEDs and turn motors ON or OFF through relays or other devices. This project drives LEDs using two ports and four ports unused. Connected to push switches are the two other ports used as inputs.

The PCF8574 I2C chip provides 8 bidirectional binary ports which can be connected to the sensor port’s 4.3V supply directly since it requires a supply voltage of 2.5V-6V. It can drive LEDs directly as it supplies 25mA to each port. Higher loads can be driven by connecting pairs of outputs in parallel.

On the I2C, a clock signal is carried by one wire and the data signals by the other one since it is a 2-wire serial bus. It has one master communicating with slave devices.

Rest of the project