Logging temperature meter (ltm) is a ESP8266 based temperature measurement and logging device.
The project is based on port of an existing ESP8266 Arduino project, and consideration was given to migration to the ESP32 hardware platform, but there are large differences to the WiFi related libraries… so for now, ESP8266 looks ok. There remain development options for multi channel logging if needed.
Design criteria
The design criteria are:
- small, portable, battery powered;
- direct reading temperature scale;
- flexibility for a range of sensors;
- local display including bar graph, time, and temperature;
- log measurements to a serial port of some kind;
- offer remote access for recent measurement log.
Algorithms
The initial algorithm implemented is for a negative temperature coefficient (NTC) thermistor using the single ADC port on the ESP8266. The code uses the Steinhart-Hart model to solve for temperature.
Above is a plot of the Steinhart-Hart model (red) and the so-called B equation (green) for the NTC used in my car. They are quite similar in this case, but the Steinhart-Hart model is more accurate.
Prototype
The prototype is based on a port of RF Power Meter 2 (RFPM2). Since advice is that SPIFFS is deprecated on ESP8266, it has been replaced by LittleFS.
Above, a breadboard prototype of ltm. The time is obtained from the Internet (if possible, so you see UTC displayed, and the clock is used to timestamp observations. The bar chart is 3°/div, fsd=120°.
Above is a partial screenshot of the web log interface.
The same data is streamed out the USB serial port.
Configuration / calibration data for each sensor is held in a file stored on the ESP8266. Configuration is done from the web interface by selecting the required configuation file.
Above is a partial screenshot of the web screen for selection of the active configuration.
A work in progress…