I2C Breakout

The saga continues : Sometimes it takes a lot longer than expected to make a MEEPS board ready to deliver. The I2C Breakout board is a perfect example. About 10 months ago we enthousiastically announced the board but it was really difficult to get it reliable enough to deliver. The problem was the type of crystal that is necessary for the MCP79410 Real Time Clock to work reliably. The datasheet said that the MCP79410 is able to work with either a 12.5pF or a 6pF crystal. We first started with a 12.5pF crystal, it was so inaccurate that it was unworkable even with soft-calibration; it was about two seconds too fast a day which also couldn't be solved through the tweeking of the capacitors. In the end we settled for a 7pF cristal of Citizen that gave the MCP79410 the necessary accuracy. Together with the soft-calibration we have a reproducable accuracy now. In the current datasheet of Microchip there's no mention anymore of 12.5pF crystals. The MEEPS I2C Breakout board contains a Microchip MCP79410 I2C Real Time Clock (RTC), an Analog Devices AD7415 I2C temperature sensor, a Microchip 24AA08 I2C EEPROM and a Microchip I2C MCP23008 I/O Expander. The RTC is equipped with a backup battery that should be able to go on for more than 2 years. Through jumpers (shunts) all IC's are fully configurable, there are also jumpers on the board for the termination of I2C bus. Because the board is fully designed with SMD components we choose to deliver it fully built and tested.