GitHub - netphantm/Arduino_thermostat: WeMos+DS18B20 thermostat with logging

DS18B20 thermostat with logging

ESP8266 thermostat with DS18B20 oneWire sensor

This is a 'simple' thermostat controller, using a DS18B20 oneWire temperature sensor on a WeMos D1 Mini Pro. The DS18B20 has a +/-0.5 °C tolerance and is perfectly stable (and even cheaper). I tried it first with an DHT11 sensor, but it's very unreliable, unstable and has a +/-2 °C tolerance (and who needs a humidity sensor anyway, except perhaps if you use it in a sauna).

It uses two relays for safety reasons, to be sure that there is no current on either one of the power lines when switched off. I couldn't find a shield with two relays, so I bought it as a kit and soldered all components to the board myself (relays, terminal strip, and the fun part: the SMD components). It just had to be rewired to switch two separate wires independently, instead of switching current from the same wire to two different consumers.

The thermostat will power up the relays if the temperature is greater than temp_max and power off if temperature falls below temp_min if the appliance is set as a cooler, and accordingly, power them up if temperature falls below temp_min and power off if the temperature is greater than temp_max if set as a heater.

The www branch contains the (php) files needed for the webserver (get log data, keep settings, render Google graph, provide a settings form for one or more such devices). In the settings form, some standard values are filled in, some basic checks performed and the SHA1 fingerprint is calculated from the server's certificate (to make sure the WeMos sends the data to the right logserver).

The display shows following data: the SSID (if connected to WiFi, or the IP and credentials for the AP it provides in config mode), the LAN IP, the outside IP (which it refreshes only once an hour, to not get banned from ipinfo.io), the temperature (also min/max on the large display), the device type (heater/cooler), the relais state (On/Off) and the current operating mode (manual/automatic).

A capacitive touch sensor toggles the relay if pressed less than 500ms thus changing to manual operating mode (means that relais isn't controlled by the temperature readings anymore). If held longer than 500ms, it switches back to automatic mode. I used touch sensors because I didn't have buttons, but it's way cooler with touch sensors anyway. The main advantage is, you don't have to bore holes for the buttons, just stick them to the inner side of the enclosure and add appropriate stickers to the outside.

I know that there are simpler or fancyer methods to do some of this (like OpenHAB, Blynk, etc.), but I wanted to do it all by myself with already available services, as an exercise, and to learn stuff in the process (so please don't contact me with such tips). All other feedback is welcome.

Features

.96" B/W or 1.44" color TFT display for: SSID, LAN and internet IP, temperature, mode (man/auto) and relay status
Uses WiFiManager library, so you don't have to hardcode the WiFi credentials
Uses a webserver to log the measurements (HTTPS)
Compares the logservers certificate SHA1 fingerprint with the one provided in the settings
Progress bar on the serial console, showing time percentage until next log update
Manual relay override via capacitive touch sensor; press longer than 1s to switch back to automatic mode
Option to change between 'cooler' and 'heater' thermostats (fire up on temp >= temp_max or temp <= temp_min)
Draws a google graph from the logged data and a gauge which also shows hysteresis
Shows last update date/time in the browser's timezone
Settings button on the webpage, which opens the device's settings page
Provides a setup page for configuration variables that are sent to the WeMos, which then stores them as JSON to the webserver and SPIFFS:
- WeMos D1 hostname (in case you have more than one device logging to the same webserver)
- SHA1 fingerprint (calculated by the php script from localhosts certificate)
- Logserver hostname
- Logserver port (HTTPS)
- Refresh/sensor reading interval
- Minimum/maximum temperature values for the hysteresis
- Temperature deviation for calibrating the sensor
- Thermostat device type (cooler/heater)
- Operation mode (manual/automatic)
- Time interval between measurements.

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Libraries needed

WiFiManager
ESP8266HTTPClient
ESP8266WebServer
ESP8266mDNS
FS
OneWire
DallasTemperature
ArduinoJson
Adafruit_GFX
Adafruit_ST7735
SPI
TFT_eSPI

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TODO

Clean up code and add comments
CSS-styled mouseover tooltip for the graph, including relay status
Change the graph's time range, enable zooming and panning
Change the horrible design (now I've added even more of it)
Responsive design for mobile devices
(Perhaps) Enable OTA
(Perhaps) Keep log data in a local file if logserver is not reachable and send it all when connectivity is restored
(Perhaps) Documentation, including 'fritzing'. In the mean time, look at my sources in the Links (software) below (fritzing should be pretty straight forward anyway)
(Perhaps) Change checking logserver validity from comparing SHA1 fingerprint, to check against an uploaded CA certificate (longer validity then a letsencrypt signed certificate)