I saw the idea of using a capacitor and timer to coerce an analog pin, but the accuracy and issues with processor lags scared me off. I will likely do a ‘bake off’ with the I2C sensor and this method and see how they compare, nothing to loose since I have the photocell and can probably scrounge a capacitor. Have you ever tried this, how well did it work?
I missed the SDFat and other postings, will definitely have to look into that as it would greatly simplify the architecture and keep all data local. Thanks for the reference! If do this, then we definitely need to get into discussions on file formats.
Just stumbled over another problem (minor) which is the flip side of the analog read - controlling fans. I have had my circulation fan hard wired to GND and 5v, but was thinking of an analog pin for the exhaust fan: 1) There is no analog out (though can fake it with a capacitor), 2) Raspberry only has 3v on the GIPO, which would cut the speed by 1/4 of normal (12v). I hate adding more stuff, but seriously thinking of a 12v PWM fan with power from a wall wart and hooking the PWM to a pin. I believe @Webb.Peter used this trick on his early growth boxes. Might just do both fans this way, for consistency; and it would allow experimenting with the circulation fan and its affects on plant strength. Any opinions or thoughts?