ESP-TMEP

ESP-TMEP is firmware for ESP8266, which can measure temperature using DS18B20 and send it to the TMEP.CZ online service or any other service that accepts HTTP GET requests.

Build video and basic information about this project (in Czech) is on my blog and the Z-TECH YouTube channel:

• Jak vyrobit Internetový teploměr pro TMEP.CZ ze třech součástek
• Vylepšení internetového teploměru ESP-TMEP
• Aktualizace internetového teploměru ESP-TMEP
• ESP-TMEP: Timeout konfigurace a průměrování hodnot

Features and limitations

Features

• Support for common DS18B20 temperature sensors.
• User-friendly deployment (no need to modify code, easy configuration via web browser).
• Can send values to three URLs.
• Reboots every 29 hours to maintain stability.
• Measures temperature as a rolling average over 1 minute to compensate for measuring errors.

Limitations

• No server certificate validation is performed, because on ESP8266 it's practically impossible.
• Internal web server is HTTP only; again, because proper HTTPS is almost impossible on ESP8266.
• Some parameters are still hardcoded:
  • Interval in which data are measured and sent (always 60 seconds).
  • Remote server protocol (always uses HTTPS).
  • Remote server timeout.

Usage

Configuration mode

After first startup, the device boots into configuration mode. It creates an Wi-Fi access point named ESP-TMEP-xxxxxxxx (where xxxxxxxx stands for unique chip ID). After connecting, you'll see the configuration UI. In addition to network name and password, you can configure the following options:

Name	Example	Size	Description
Remote host name	demo.tmep.cz	100	Host name part of the target URI
Remote host path	/?temp=	100	Path part of the target URI
Configuration PIN	AbXy1234	20	PIN/password for configuration reset

The target URI is constructed by joining the parameters and measured value in °C:

Scheme	Host	Path	Value
https://	demo.tmep.cz	/?temp=	22.63

You can define up to three URLs.

Operational mode

Device then restarts to operational mode. In this mode, in addition to sending the measurement to remote servers, runs a local web server, offering the following services:

URI	Description
/	Homepage showing current temperature
/api	JSON API endpoint
/reset?pin=XXX	Switch to configuration mode

JSON API

The response has the following format:

{
    "temp" : 22.63,
    "deviceId" : "ESP-TMEP-xxxxxxxx",
    "version" : "2.2.0"
}

• temp is last measured temperature in °C
• deviceId is unique device identifier (xxxxxxxx is chip ID)
• version is firmware version

LED status

Device status is indicated by the builtin LED. There is a number of 250 ms flashes rougly once per second:

Flashes	Meaning
1	Normal operation
2	Sensor error
3	Remote server connection error
4	Remote server connection timeout
permanent on	Wi-Fi connecting or config required
fast blinking	Internal error in SPIFFS

Hardware

Any board with ESP8266 chip can be used. I'm using LOLIN/Wemos D1 mini.

Hardware connections (the wire color column refers to common wire colors of the waterproofed version of DS18B20):

D1 Mini	DS18B20	Wire color
G	GND	black
5V	VDD	red
D2	DQ	yellow

Additionally connect 4k7 resistor between VDD/5V and DQ/D2.

Case

I'm using this WeMos D1 mini Enclosure by 100prznt.

Software

This firmware is using ESP8266 Arduino Core 3.1.2. The following external libraries are required:

• ArduinoJson (tested with version 7.0.2)
• DallasTemperature (tested with version 3.9.0)
• OneWire (tested with version 2.3.7)
• WiFiManager (tested with version 2.0.16-rc2)