21: Battery Backup, Revised Again
updated 9/26

After my failures with the Adafruit Powerboost 1000 (post 16), I complained at an Adafruit forum. Their response as  that I should have used a Powerboost 1000C instead. Note the subtly added letter "C". So, gritting my teeth, I paid $19.99 (plus their pricey shipping) and tried again.

I let this setup run for over 24 hours powering either a Raspberry Pi (drawing about .4 amps) or a Particle Photon (drawing 1/8th as much) and both worked fine. I could disconnect external USB without the computers noticing but pulling the battery plug caused both processors to restart. Not nice but not a deal killer.

Note the input power LED in the image. If you aimed a photo sensor at it, your program could detect external power failure. You would  then have time to send out a text message and shut down "gracefully" whatever that means.

Update: The setup ran a Raspberry Pi for over 2 weeks.

20: I Installed a LIVE System!

(after 2+ years of messing around)

Two weeks ago I installed Particle Photon in my granddaughter's farm hoop house (they used to be called "green houses"). It is programmed to support 2 temperature sensors and 2 soil moisture sensors. It provides control of 2 switched devices: an electrified deer fence and a water valve for drip irrigation. Here's the smartphone web page image:

as of 10pm, September 15

Data comes from my Photon program via Particle's "cloud" interface. The electric fence is normally turned on and off by time-of-day (the cloud provides UNIX-like time functions). But that timing can be overridden by the web page above (password secured).

I originally planned to implement this using a Raspberry Pi but the $19 Photon's simple web interface trumped the Pi's many advantages (especially the mature software development environment).

However, the Pi is not all together out of the picture: a Pi-based cron task checks on the Photon every few minutes and sends text messages if anything has gone wrong.

The Photon, sensors, switches and wiring cost under $70. My control program in C++ is about 80 lines long.

Does anyone know of a reliable motor setup for safely rolling the sides of the hoop house up and down (to control inside temperature)?