kflynn/hydro

ESP8266 hydroponic controller

ESP8266 hydroponics controller

This is code to let an ESP8266 controller manage a small hydroponics garden.

You'd like to think that this would be mindnumbingly simple, and in one respect you'd be correct: NodeMCU makes a lot of this stuff really easy.

On the other hand, the moment computers have to handle the passage of time, life gets pretty miserable, and this is no exception. Most of the complexity here is:

1. Sync the clock using NTP, but only when we need to.

2. Manage the fact that the pump cycles happen on scales of hours, while the RTC needs attention on scales of seconds.

3. Don't leave the controller running when there's nothing to do. (This is kind of unnecessary for this project, since the pump runs on mains current anyway, but it's the right habit to be in for IoT stuff.)

Note that the ESP8266 doesn't actually have a Real Hardware RTC. This implies that we need to sync to NTP more often than we'd otherwise need to, and further implies that we have to take special care to make sure we sync at least once after the first dsleep cycle...

...except that these days we're just using tmr.alarm() instead of rtctime.dsleep() anyway, because using dsleep() resets the GPIO pin that we want to use as the relay output! So we'd need to use tmr.alarm() while the pump is running anyway... so forget it, we'll just use it all the time.

WiFi Stuff

init.lua relies on wifi.lc to get WiFi running, but you might note that wifi.lua isn't checked in. That's intentional, because otherwise I'd be saving WiFi keys in GitHub.

You can look at wifi-example.lua for an example wifi.lua.

Running the system

• Provide a wifi.lua.
• Edit pin numbers to taste in main.lua, towards the bottom.
• Plug in!

If the pin labelled GPIO12 on the board (NodeMCU pin 6 -- why did they DO that??) is pulled to ground, the system will not actually start. This is a disaster-recovery utility.

Software design

On boot, init.lua gets control and creates the INITHOOKS table. Everything in the system that needs to run bootstrap code registers it in that table:

• init.lua uses it to initialize the RTC and the state FIFO
• main.lua uses it to:
  • get the state machine set up (again)
  • initialize the pump
  • finally start the state machine actually running

The state machine controls the world, and is asynchronous: see State.lua for more, but basically we use the ESP8266 RTC fifo to manage state transitions. We handle WiFi, NTP, and time in general with the state machine.