I2C Breakout

  • Print

First view : There was a need for a I2C Real Time Clock (RTC) within MEEPS and which one do you choose? A NXP type like the PCF8583? In the datasheet you always see a trimmer to tune the precision of the IC, always a little bit to fast or a little bit to slow but never exact without the right measuring equipment. A Dallas (taken over by Maxim nowadays) DS1307 RTC then? It's very nice with backup battery and with the correct crystal very precise. We've used them a lot and it really is a good RTC IC. The disadvantages are that the price was always a little bit high and the DS1307 only supports the 100kHz I2C speed. During our search we found the MCP79410, it looks a lot like the DS1307 but is much more modern. It also has a connection for a backup battery and the pinout is the same as the DS1307. Only the SQW (SQuare Wave) output, that only could output a square wave signal, is replaced by a MFP (Multi Function Pin). You can use it the same way as with the DS1307, as a square wave output, but you can also program it as an interrupt pin; the MCP79410 has 2 alarms onboard. The only disadvantage is that the MCP79410 is only manufactured in SMD housing, a DIP version is not available. We were so convinced by this IC that we went all the way. There is of course a whole lot of room left on the PCB that has the standard 5x8cm MEEPS form factor (1/4 Eurocard). That extra space is used for an AD7415 temperature sensor of Analog Devices in a SOT23-5 housing, a 24AA08 8kbit EEprom of Microchip also in a SOT23-5 housing and for some extra I/O like pushbuttons, LED's and buzzers a MCP23008 of Microchip in a SOIC-18 housing. For the MCP79410 RTC we also mounted a CR1632 backup battery which should last about 2 years. The IC's are completely configurable with jumpers these are for the I2C addresses, the WP of the 24AA08 EEprom and the MFP interrupt possibility of the MCP79410. We named this MEEPS board I2C Breakout because only I2C RTC wouldn't give it enough credit. A first view...