[Stewart Allen] acquired a Mindstorm kit about a month ago and he’s already building his own sensors for it. He wanted a more accurate range finder with a narrower measurement field than the stock sensor. Mindstorm has the option to communicate with sensors via an I2C bus. [Stewart] set up an ATtiny45 to act as a the slave on the bus, facilitating the analog measurement of the distance voltage by using and lookup table, and handling the data transfer with the NXT brick. His testing setup is pictured above, with an AVR Dragon for programming the tiny45 and a Bus Pirate for sniffing the I2C data during the development process. The sensor, looking great on a professionally made PCB he ordered, requires a simple driver that [Stewart] hammered out for use with leJOS, the alternative Mindstorm firmware we’ve seen before.