I just finished my NB1A board which has a DS1337 RTC (two time-of-day
interrupts and a battery backup) and a TI TLV5620 quad 8-bit DAC.
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The schematics and board layout are in the datasheet. Also on the
website are four Arduino libraries and three application examples.
The libraries are
TWI ... code from AVR315 (cosmetic modifications)
SPI ... SPI interface
RTC ... code for the DS1337
DAC ... code for the TI TLV5620 DAC.
The examples are --
nb1a_dac_r0 ... initializes the TLV5620 and sets
output voltages
nb1a_rtc_r0 ... setup for the DS1337 and outputs
date and time to the serial port
nb1a_rtc_alarm_r0 ... sets up alarm1 interrupt
on the DS1337. Outputs the string
"*** ALARM ***" when the interrupt
is triggered.
The documentation is sparse but I will be updating it over the next month.
Good stuff, I like it.
From the schematic, the CR1220 battery seems to be the only power source, so it would not be a "backup battery", would it?
From the datasheet, the "normal" (I2C interface active) power consumption is about 150 micro Amps. That would make the CR1220 (40mAh) last about 266 hours (12 days). I was wondering if you considered placing the battery as a real "backup", with a diode in series, which should have saved the battery when the board is powered.
The 150uA is only when the I2C bus is active and at 400KHz. Unless you are continuously communicating on the I2C bus you will have much lower currents.
I have had two boards on my desk for over a month and the battery voltage is
still over 3V. I assumed the duty-cycle would be fairy low so there would not be a problem.
I will take a look at the diode and see if there are any other issues beyond the
Vf drop. I am also considering using a transistor to enable/disable the I2C going to DS1337.