Logging temperature meter (ltm) v1 – DS1820B support

Logging temperature meter (ltm) is a ESP8266 based temperature measurement and logging device.

Above is the prototype.

The ESP8266 incorporates a single 10bit SA ADC with a single input, and the prototype on the development board suffers serious noise from the WiFi operation.

One option explored is to shut the Wifi down and rely upon the LCD display and USB serial log for better noise performance.

Another option is to use a digitial temperature sensor. This article describes performance using the inexpensive Maxim DS1820B OneWire digital sensor usable from -55-125° C.

In this test it is used with 3.3V pullup from the dev board. It is possible to configure these for parasitic power, and the firmware is written for that, but Maxim advise against parasitic power above 100°.

Above is a chart of just over 2160 observations captured over six hours in my office (WiFi on max power), the bump is the heating coming on at the start of day. The probe is 400mm above the floor and warmed by running equipment, so the temperature variation is somewhat reduced.

The firmware is configured to use the DS1820B in 11 bit mode, which means resolution is °/8, and the ltm output is formatted to 0.1° resolution. The chart is quite stable, measurement noise is mostly a result of slow change in temperature creating 0.1-0.3° steps in the formatted output.

The DS1820B mode code was also tested on an ESP-01S (without LCD connected as there aren’t sufficient pins) and worked fine, these sell for a few dollars on eBay.

A work in progress…