Back in June and July 2005, we described a low-cost, high-performance development board from JED Microprocessors based on the popular ATmega32 microcontroller. Since then, JED have produced a complete range of add-on modules for the AVR200, most of which can be purchased in kit form.

Included in the range are prototype, I/O expansion, non-volatile memory, keypad and LCD interface boards. All boards communicate via the I²C (TWI) serial bus, with the prototype and memory boards plugging directly into the AVR200’s "upstairs" connector (J14).

All other boards connect via the AVR200’s 10-way I²C header (J6) and use the Philips 82B715 bus extender IC for communication at up to 100m (at the 71kHz data rate) from the AVR200 using ordinary ribbon cable. Note that as the I²C bus frequency is reduced this distance will increase; refer to the Philips application note AN10216 (available from www.semiconductors.philips.com) for specific details.

All remote boards are based around the PCF8574 or PCF8574A 8-bit I/O expander IC. Essentially, these ICs act as addressable nodes with eight input/output lines. Most boards include two I²C headers, allowing subsequent boards to be wired together in daisy-chain fashion. This makes for a truly simple and flexible expansion system. Let’s look at each board in a little more detail.