The I/O expander does sound like the way to go. I am not getting the board assembled, but am comfortable soldering SMD parts by hand. It's tricky but with the right technique and patience I have been able to solder small parts such as SOT-23, and SOP-8.
I have never used I/O expanders, but think I2C would be my preferred choice. I will do some research these and see about integrating one in the project. This would also allow for more GPIO on the external pin header!
It's true it would be best to have a separate battery for the RTC, I will see if I can fit it on the board. But so far I have been thinking just running it off the main battery. With Pico powered down via the button (3.3v_EN LOW), the entire circuit draws about 135uA, which would last about 70 days before the battery dies. If the power switch is off (no power to Pico at all, just power to the LDO and RTC), the current draw is under 20uA. It would take over a year for the LDO and RTC to kill the battery if it was half way charged. With the solar cell, if the cell was pointing up, it would never lose charge.
If it's not feasible to fit a coin cell battery in, my original plan was to have the Pico shut down if battery voltage drops below 3.5 volts. This would reduce the runtime for sure, but would also be easier on the battery and ensure the RTC never runs out of battery.
I have never used I/O expanders, but think I2C would be my preferred choice. I will do some research these and see about integrating one in the project. This would also allow for more GPIO on the external pin header!
It's true it would be best to have a separate battery for the RTC, I will see if I can fit it on the board. But so far I have been thinking just running it off the main battery. With Pico powered down via the button (3.3v_EN LOW), the entire circuit draws about 135uA, which would last about 70 days before the battery dies. If the power switch is off (no power to Pico at all, just power to the LDO and RTC), the current draw is under 20uA. It would take over a year for the LDO and RTC to kill the battery if it was half way charged. With the solar cell, if the cell was pointing up, it would never lose charge.
If it's not feasible to fit a coin cell battery in, my original plan was to have the Pico shut down if battery voltage drops below 3.5 volts. This would reduce the runtime for sure, but would also be easier on the battery and ensure the RTC never runs out of battery.
Statistics: Posted by picoprojectmaker — Tue Jan 16, 2024 2:39 am