I would like to have a RTC alarm turn on my arduino at a specified time each day. I know that Arduino has good sleep modes but I'm concerned even with the quiescent power consumption from the voltage regulator due to feeding Arduino with 9V (this is my only option). My preference is to completely shut off the arduino board by removing all power to it.
So my thought is to use a RTC that has an alarm to somehow trigger the Arduino to turn on. I'm completely unfamiliar with MOSFETS and relays but I think these are options for my problem.
Does anyone have any suggestions?
Best Answer
Here is my solution for anyone who is curious. I have a DS1305 RTC running off a 3V coin cell and have the RTC's INT0 pin pulled up to 5V. INT0 is the alarm interrupt pin. This pin is at high impedance when the alarm time has not been reached and becomes a open drain when the alarm time has been reached (alarm is ringing). Because the INT0 pin is high impedance, it is consuming almost zero current. The 5V is being delivered from a MAX8881 ultra-low Iq regulator rather than the standard Arduino regulator. So for these two reasons, when the device is still sleeping it is consuming only a few microamps.
The next step is to use that alarm to wake everything up. Between my regulator and my main ATMega chip I have a p-channel MOSFET which has its gate connected to the RTC's INT0 pin. So when the alarm time is met, INT0 becomes a common collector bringing the p-ch MOSFET's gate to 0V thus closing the switch and allowing 5V to be delivered to ATMega.