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In this project I created an infrared (IR) link that provides bi-directional communication between the NXT and the new Power-Functions system, which consists of a battery box, motors, a remote control (an IR transmitter) and an IR receiver that controls the motors.

I previously built an IR transmitter for the NXT which used an MSP430 microcontroller and which was able to send Sony IR commands (the specifications of this protocol are widely available). In this project, I wanted to achieve three additional goals:

* To analyse the Power-Functions IR protocol, for which no documentation is publicly available.
* To build a system that could not only send IR commands, but could also receive and decode them.
* To experiment with AVR’s, another family of microcontrollers.

There were several reasons that I wanted to experiment with the AVR’s. Compared to the MSP430 microcontrollers, the AVR family offers many more chips in DIP packages (large but easy to prototype with), they run at wider supply voltages (most can tolerate at least 2.7-5.5V and some operate down to 1.8V), and their pins can supply a lot of current (up to 40mA for a single pin). The wide range of supply voltages means that they can be connected to the 4.3V supply of the NXT’s ports directly without a regulator, and the ability of the pins to supply a lot of current simplifies some circuits, such as when the chip needs to drive a bipolar transistor or a LED. Another advantage of the AVR is that they can be programmed using a wide variety of simple circuits, not just with proprietary programming devices. [via]

An Infra-Red Link Using an AVR – [Link]