{"id":1809,"date":"2021-01-26T11:33:57","date_gmt":"2021-01-26T17:33:57","guid":{"rendered":"http:\/\/jimlund.org\/blog\/?page_id=1809"},"modified":"2023-08-06T23:18:38","modified_gmt":"2023-08-07T04:18:38","slug":"esp32-kiln-controller","status":"publish","type":"page","link":"https:\/\/jimlund.org\/blog\/?page_id=1809","title":{"rendered":"ESP32 Kiln controller"},"content":{"rendered":"\n

This project connects an ESP32 S2 on an ESP32-S2 Saola-1 development board to a Temperature controller, and has WiFi to provide remote monitoring and programming of the kiln.

The kiln was fit with a Solo SL4848-VR temperature controller connected to two SLR relays that control the kiln coils.

The SL4848 has RS-485 output, and is connected to a generic RS-485 to serial USART module (MAX485), and then connected to two pins on ESP32 configured as a USART. The ESP32 communicates using the Modbus protocol with the SL4848. <\/p>\n\n\n\n

The ESP32 is running software written using the Arduino IDE that connects to WiFi and acts as a web server. The web page shows a graph of the programmed and actual temperature and allows the SL4848 program to be updated. The ESP32 is powered by a reused wall wart (5V, 800mA output).<\/p>\n\n\n\n

TODO<\/strong>
1. Add current sensors. Track coil aging and power use.
2. Have the ESP32 save programs.
3. Record of runs.
4. Start as an access point, have user set ssid\/passwd, then connect to the local network for a normal run.
5. Done! Show state at top: temp, program segment, time, set point, current draw.
6. Adjust PID params to follow temp program better. [Not really needed. After auto-setting the PIDs for 500F, 1000F, 1250F, 1500F, and then setting temp points every 30 min, it follows pretty closely on the heating side.]
<\/p>\n\n\n\n

<\/p>\n\n\n\n

Update on setup process, 2022<\/strong>
1. Add ‘Additional Boards Manager’ in Prefs: https:\/\/raw.githubusercontent.com\/espressif\/arduino-esp32\/gh-pages\/package_esp32_dev_index.json
2. Install library AsyncHTTPRequest_Generic from library manager.
3. Install AyncTCP from git to Arduino\/libraries\/ dir: https:\/\/github.com\/me-no-dev\/AsyncTCP
Now it builds!
4. Enable PSRAM in Arduino->Tools. Use default partition scheme.
<\/p>\n\n\n\n

<\/p>\n\n\n\n

Getting ESP32 dev environment going<\/strong>
Installed the Arduino IDE, but no support for the S2 board.

Installing the ESP idf allowed command line programming to work, got the Blink program working.
https:\/\/github.com\/espressif\/esp-idf\/release<\/a><\/p>\n\n\n\n

mkdir -p ~\/Documents\/Arduino\/hardware\/espressif && cd ~\/Documents\/Arduino\/hardware\/espressif && git clone https:\/\/github.com\/espressif\/arduino-esp32.git esp32 && cd esp32 && git submodule update --init --recursive && cd tools && python get.py
 
git clone https:\/\/github.com\/espressif\/arduino-esp32.git esp32s2 
git submodule update --init --recursive<\/pre>\n\n\n\n
Then follow these directions to get it to work with the Arduino IDE, link<\/a>.
Download xtensa-esp32s2-elf and the latest esptool, copy to .\/Documents\/Arduino\/hardware\/espressif\/esp32<\/p>\n\n\n\n
To get it working with the IDE, tried a few things and finally got it working.
\nInstalled the esp32s2 repository with git:<\/p>\n\n\n\n
wget https:\/\/github.com\/espressif\/crosstool-NG\/releases\/download\/esp-2020r3\/xtensa-esp32s2-elf-gcc8_4_0-esp-2020r3-macos.tar.gz
   wget https:\/\/github.com\/espressif\/esptool\/archive\/v3.0.tar.gz<\/p>\n\n\n\n
Run Blink (add “define LED_BUILTIN 5”), LED blinks!
Run WiFiScan, works!<\/p>\n\n\n\n
Date\/Time
Got date\/time setting via NTP working with these examples, 1<\/a>, 2<\/a><\/p>\n\n\n\n
Tried several Modbus libraries but they didn’t work.  Some weren’t supported on ESP32.  After trying different libraries for a while, I switched the controller to ASCII and started sending requests using my own code.
The final step in getting it working was to switch the TX\/DX connection at the RS-485 to USART breakout board.<\/p>\n\n\n\n
Hardware<\/strong>
Solo SL4848-VR (manual<\/a>), $60 on ebay.  Supports Modbus communications over RS-485, supports both RTU and ASCII.

RS-485 to USART module (link<\/a>), 5 for $7.

ESP32 S2 Saola-1 development board (link<\/a>), $14.50.  Docs link<\/a>.
Bare ESP32 S2 module (link<\/a>), $4.
WiFi uFL antenna (link<\/a>), $3<\/p>\n\n\n\n
Modbus<\/strong>
Need to  terminate line at each end.  RS485 can drive about 50 ohms total, or  doubly terminated with 100 ohms.  Typical value is 120 Ohm resistors at  each end.
Info: Modbus ASCII vs Modbus RTU<\/a>, Modbus protocol<\/a>, Modbus ASCII<\/a>
Modbus ASCII, send each byte as two ASCII hex digits.  One checksum byte, a LRC<\/p>\n\n\n\n
To calculate the LRC:<\/p>\n\n\n\n
  1. Add up all the data bytes in the message (before converting to ASCII and without the initial colon and final CR\/LF).<\/li>
  2. Throw away any bits that carry over 8 bits.<\/li>
  3. Make the result negative (by twos compliment) to get the LRC byte.<\/li><\/ol>\n\n\n\n
    Example: “: 01  03  10  00  00  03  7E  CR LF” (without the spaces).
    : Start of message
    01 ID
    03 Read Holding Register
    10 00 Register address
    00 03 Request 3 registers
    7E Checksum byte (incorrect here)
    CR LF End of message, bytes 0D 0A

    Response example: “:0103022328AF” — ID, request code, bytes in response, data bytes (2328), LRC (AF)<\/p>\n\n\n\n
    Solo controller setup<\/strong>
     C-sl — Modbus Protocol (ASCII or RTU)
     C-no — Network address (1-247)
     bps — Baud rate 
     len — Bit length (7\/8)
     Prty  — Parity (None\/Even\/Odd)
     Stop — STOP BIT (1\/2)

    Register conventions:<\/p>\n\n\n\n