Temperature control system for use in a remote location (e.g. a mountain cabin).
The system consists of an ESP32 microcontroller from Espressif and one or more Dallas/Maxim DS18B20 digital temperature sensors. The desired temperature is achieved by continuously switching on/off one or more electrical heaters using Nexa power plugs (over RF 433 MHz). The ESP32 device periodically connects to the Internet over WiFi, logging the current temperature into a Google spreadsheet. The spreadsheet is also used for setting the desired temperature, which will be transferred to the device during the next synchronization.
The ESP32 code is written in Arduino-style C/C++. Integration with Google spreadsheet is done using Google Apps Script (javascript).
The top section displays current date and time. This is updated using NTP, and will be automatically adjusted for DST (daylight saving time). The main temperature is displayed in yellow. Below, the display will cycle through any additional temperature sensors.
The currently set temperature is displayed, and the current temperature mode is indicated:
- 🟦 🌙: frost protection
- 🟥 ☀️: comfort mode
The bottom line displays the current status of configured power plugs:
- ○: off
- ●: on
The current device activity is displayed at bottom right:
- Nexa: Device is transmitting control signals to power plugs (every 5 minutes)
- WiFi: Device is connecting to WiFi
- Time: Device is updating time from NTP (once per day)
- Sync: Device is synchronizing with Google spreadsheet
- <time>: Device uptime is displayed when the device is "idle" (only monitoring temperatures)
The two buttons are used for adjusting the desired temperature locally (when you are on-site):
- M: Toggle between temperature modes: frost protection / comfort mode
- +: Increment desired temperature for the currently selected mode. The temperature will roll over from max to min (e.g. 16, 17, ... 24, 25, 16, 17, ...)
- Note! The buttons control the first configured zone (index 0), so this need to be the primary temperature zone.
Temperatures will be appended to sheet '<yyyy-mm>' in the configured Google spreadsheet (the sheet will be created if it doesn't exist):
Configuration will be read from the sheet 'config', columns A and B (a sheet with default values will be created if it doesn't exist):
- Last Sync: Timestamp of last sync
- Uptime: Reported uptime from device
- Error Count: Errors counted by device (e.g. HTTP timeout)
- Sync Interval: Interval between each synchronization (in minutes)
- <Name> !: Set (desired) temperature for temperature zone or value (0/1) for manual zone.
- This value is normally read from the sheet and synced towards the device
- If the value is changed locally at the device (using the buttons), then the value in the sheet will be updated correspondingly
- If a formula was used to calculate the cell value (e.g. from a reported temperature), then this formula may get overwritten
- <Name> °C: Last reported temperature of zone <Name>
- <Name> %: Last reported duty cycle of zone <Name> (percentage heat-on)
- ...
TODO! Update screenshot
There is also a utility menu system that is invoked by pressing one of the buttons within a couple of seconds after powering up the device.
You control the menu system using the two buttons:
- M: Skip to next menu item
- +: Invoke function
The menu system contains functionality for:
- Reading addresses of connected temperature sensors
- Manually switching Nexa power plugs on/off. This is useful for testing RF communication, and for programming the Nexa Self-Learning power plugs
LilyGO TTGO T-display ESP32 GitHub
It might be better to use a straight solid core wire antenna (quarter wave-length, 17.3 cm), rather than the antenna coil shown on the picture.
- Install/update the Arduino IDE
- In Preferences set Additional Board Manager URLs to
https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json - Go to Tools > Board > Boards Manager and install esp32 by Espressif Systems
- Go to Tools > Board > ESP32 Arduino and select the board ESP32 Dev Module
- The board shall be configured like this:
- Board: ESP32 Dev Module
- Upload Speed: 921600
- CPU Frequency: 240MHz (WiFi/BT)
- Flash Frequency: 80MHz
- Flash Mode: QIO
- Flash Size: 4MB (32Mb)
- Partition Scheme: Default 4MB with spiffs (1.2MB APP/1.5 SPIFFS)
- Core Debug Level: None
- PSRAM: Disabled
- Arduino runs on: Core 1
- Events runs on: Core 1
- Port: (the COM port your board has connected to, see below)
- To determine on which COM port your board connects, do the following steps:
- If required, install UART driver
- Unplug the board
- Have a look at Tools > Port and remember which ports you see
- Plug in the board to the USB port
- Look again at Tools > Port
- The newly added COM port is the COM port of your board and the one you can select
Go to Tools > Manage libraries and install the following libraries:
- TFT_eSPI by Bodmer
- DallasTemperature by Miles Burton, Tim Newsomem, etc.
- OneWire by Jim Studt, Tom Pollard, etc.
- UrlEncode by Masayuki Sugahara
- Arduino_JSON by Arduino
- Button2 by Lennart Hennigs
- Edit the file
C:/Users/%USERNAME%/Documents/Arduino/libraries/TFT_eSPI/User_Setup_Select.hand enable the custom setup file for the display://#include <User_Setup.h> #include <User_Setups/Setup25_TTGO_T_Display.h> - Setup file, alt. 1
- Setup file, alt. 2
Use the file config.h.sample to create a configuration file config.h and insert:
- WiFi connection properties
- Google Apps Script ID (see below)
- Zones:
- Format: {"Name", sensor address, {Nexa id, Nexa id}}
- Note that the first zone must be the primary temperature zone
- Sensor address (8 bytes)
- Set to 0 for manual zone without temperature sensor
- Tip! Addresses of connected sensors can be read using the utility menu system, and will be printed to serial output - use Serial Monitor at 115000 baud.
- One or two Nexa power plugs can be configured per zone:
- Nexa Self-Learning (System Nexa): 4 bytes id >= 0x00000200
- Nexa Simple: 0x000000 (H=House, U=Unit)
- Heat-Link HE35: 0x000001 (H=House, U=Unit) (e.g. A1 -> 0x1A1)
Create a Google spreadsheet with associated Apps Script:
- Create a new Google spreadsheet at Google spreadsheets
- In the spreadsheet, go to Extensions/Google Apps Script and create a new script
- Paste the content of
google-apps-script.gs - Save the script and deploy it as a Web app
- Choose Execute as yourself and access for anyone
- You must accept that the Apps Script will have access to your spreadsheets
- Save the Deployment ID in APPS_SCRIPT_ID in
config.h
- Interfacing DS18B20 1-Wire Digital Temperature Sensor with Arduino
- The complete guide for DS18B20 digital temperature sensors with Arduino
The system can communicate using the following protocols:
This protocol is used by "System Nexa" power plugs, e.g. MYCR-3500, MYCR-2300, LCMR-1000 and EYCR-2300.
BIT FORMAT:
┌───┐
'S' (sync): │ T │ 10T
┘ └───┴───┴───┴───┴───┴───┴───┴───┴───┴───
┌───┐ ┌───┐
'0' bit: │ T │ 5T │ T │ T
┘ └───┴───┴───┴───┴───┘ └───
<------physical 0------><-ph 1->
┌───┐ ┌───┐
'1' bit: │ T │ T │ T │ 5T
┘ └───┘ └───┴───┴───┴───┴───
<-ph 1-><------physical 0------>
┌───┐
'P' (pause): │ T │ 40T
┘ └───┴───┴───┴───//───┴───┴───┴───
T = 250 us
Every logical bit '0' and '1' is sent as two physical bits, where the second one is the inverse of the first one. '0' => '01', '1' => '10'.
PACKET FORMAT:
Each packet consists of a sync bit followed by 26 + 6 bits and ended by a pause bit.
Packets are sent 5 times or more (Nexa) / 6 times or more (Proove/Anslut).
┌───┬────────────────────────────┬───┬───┬────┬────┬───┐
│ S │ UUUUUUUUUUUUUUUUUUUUUUUUUU │ G │ A │ CC │ II │ P │
└───┴────────────────────────────┴───┴───┴────┴────┴───┘
Duration = (11*250) + 32*(8*250) + (41*250) = 77000 us
S = Sync bit.
U = Unique id, 26 bits. This is this code that the reciever "learns" to recognize.
G = Group bit, to address all units in group. All units = '0', one unit = '1'.
A = Activation bit. On = '0', off = '1'.
C = Channel bits. Proove/Anslut = '00', Nexa = '11'.
I = Unit bits for Proove/Anslut. 1 = '00', 2 = '01', 3 = '10', 4 = '11'.
Unit bits for Nexa. 1 = '11', 2 = '10', 3 = '01', 4 = '00'.
P = Pause bit.
This protocol is used by older type Nexa power plugs, where you set house code (A-F) and unit number (1-8) on the device, e.g. SYCR-3500.
BIT FORMAT:
┌───┐ ┌───┐
'0' bit: │ T │ 3T │ T │ 3T
┘ └───┴───┴───┘ └───┴───┴───
┌───┬───┬───┐ ┌───┬───┬───┐
'1' bit: │ 3T │ T │ 3T │ T
┘ └───┘ └───
┌───┐ ┌───┬───┬───┐
'X' bit: │ T │ 3T │ 3T │ T
┘ └───┴───┴───┘ └───
┌───┐
'P' (pause): │ T │ 32T
┘ └───┴───┴───┴───//───┴───┴───┴───
T = 350 us
PACKET FORMAT:
Each packet consists of 12 trinary bits followed by a pause (stop/sync) bit.
Packets are sent 4 times or more.
┌──────┬──────┬─────┬───┬───┐
│ HHHH │ IIII │ ??? │ A │ P │
└──────┴──────┴─────┴───┴───┘
Duration = 12*(8*350) + 33*350 = 45150 us
H = House bits. A = '0000', B = 'X000', C = '0X00', D = 'XX00', ... H = 'XXX0'.
I = Unit bits. 1 = '0000', 2 = 'X000', 3 = '0X00', 4 = 'XX00', ... 8 = 'XXX0'.
? = Unknown bits. Always '0XX'.
A = Activation bit. On = 'X', off = '0'.
P = Pause (stop/sync) bit.
This protocol is used by the older HE-35 power plug from Hellmertz Elektronik AS, where you set house code (A-F) and unit number (1-4) on the device. This power plug was previously used together with the Heat-Link temperature control system.
BIT FORMAT:
The same as Nexa Simple bit format
T = 420 us
PACKET FORMAT:
Each packet consists of 12 trinary bits followed by a pause (stop/sync) bit.
Packets are sent 7 times or more.
┌────────┬──────┬───┬───┬───┐
│ HHHHHH │ IIII │ ? │ A │ P │
└────────┴──────┴───┴───┴───┘
Duration = 12*(8*420) + 33*420 = 54180 us
H = House bits. A = '0XXXXX', B = 'X0XXXX', C = 'XX0XXX', ... F = 'XXXXX0'.
I = Unit bits. 1 = 'XXX0', 2 = 'XX0X', 3 = 'X0XX', 4 = '0XXX'.
? = Unknown bits. Always '0'.
A = Activation bit. On = 'X', off = '0'.
P = Pause (stop/sync) bit.