Here's the reference design I mentioned in
https://lowpowerlab.com/forum/index.php/topic,1579.msg11203.html#msg11203. This is pretty bare bones, but does contain a 328P processor (internally clocked at 8MHz or lower), RFM69 radio, Abracon AB1805 Ultra Low Power RTC, all operating from a CR2032 coin cell fitted on a 26mm diameter PCB. You can use either radio (RFM69W or RFM69HW), but the HW is risky due to high ESR of coin cell. Note that the radio is mounted on the underside, sandwiched between the PCB & coin cell battery holder.
The base design uses the layout I developed for the TinyTH Mote (
https://lowpowerlab.com/forum/index.php/topic,1254.0.html), with the TH sensor removed and the power sequencing circuit replaced with the controls from the RTC device.
This design, if used in RC oscillator mode only, would draw approximately 16nA while 'sleeping' since virtually all the circuitry is powered off. A more accurate Auto-calibrated RC Oscillator operation can be used with the average sleeping power running around 24nA.
The wake up timing is managed by the alarm feature of the RTC. This can provide a multitude of features like:
- Scheduled Wakeup from off condition
- Scheduled Listen Mode operation - only enable Listen Mode for a few hours a day (eg common watering cycle time)
- Scheduled interrupt of normal sleep mode, permitting fast response to wake up events at critical times of the day
- Battery backed up RAM - 256 bytes for persistent state information
- HW Watchdog Timer
The design also includes pads for an FTDI interface. The pins are not arranged in the normal in-line pattern, however, they are arranged on a 0.100 grid so that a perf board with connections such as pogo pins may be used for program load/debug.
Note that this is purely for reference purposes. No claims are made as to the accuracy or reliability of the design.
Enjoy,
Tom
UPDATE: forgot to add Watchdog feature in previous version.
(screenshot posted by Felix):