Wireless Temperature Sensor Monitoring Display

Efento wireless temperature sensors push their readings to the vendor's cloud. Chosun Gyegisa wanted those readings on a single screen at the site, so that anyone walking past could tell at a glance whether the temperature was still within a safe range.

The program polls the cloud's REST API for recent measurements, draws them as a trend graph alongside large numeric readouts, and raises an alert when the reading crosses the thresholds the operator has set. It is a Windows desktop application, built on the assumption that it stays open on a monitor and keeps running.

The readings were already reaching the cloud, but what the site needed was not a way to look them up — it was a permanent display. The screen had to be readable from a distance, with no one sitting in front of it.

The cloud offered nothing but a REST API, which left several things to handle directly:

• The sensor measures every three minutes, but transmissions are occasionally dropped, leaving gaps in the series
• Measurement timestamps from the API run nine hours behind Korean local time
• When a sensor stops reporting, the API returns stale data rather than an error

The thresholds are drawn as reference lines, with the recent temperature trend plotted over them. Markers pick out the current reading and the highest and lowest values in the window, so each can be located directly on the graph. The same values are repeated as large numbers below it.

The numeric panels resize their text to fit the window, and F5 switches to full screen, so the same layout works on monitors of any size.

When the current reading leaves the configured range, an alert badge appears on the current-temperature panel and an alert sound repeats until the reading returns to range.

Components

• Login window: opens a cloud session and sets the upper and lower thresholds
• Monitoring window: draws the graph and the numeric panels
• Cloud API module: resolves the company and sensor from the session token and fetches recent measurements
• info.ini: company name, sensor serial, display window in minutes, polling interval in minutes

Data flow

• The session token and account email obtained at login are attached to the headers of every subsequent request
• The company name and sensor serial in the config file are resolved to the cloud's company and sensor IDs
• A polling thread requests one display window's worth of measurements on each interval
• The response is converted into {minutes since the latest measurement: temperature}, gaps are filled, and the graph and panels are redrawn

Polling, screen updates, and alert playback each run on their own thread, so an active alert never stalls polling or redrawing.

• The two threshold inputs constrain each other: the upper bound cannot drop to or below the lower one, and vice versa. Changing either redraws the reference lines and panels immediately, without waiting for the next poll
• Missing samples are filled by linear interpolation written directly rather than pulled in from a library. The most frequent gap between received timestamps is taken as the sampling interval, and any expected point missing from that grid is interpolated from its neighbours
• Because the cloud's clock runs nine hours behind Korean local time, the offset is applied both when building the query range and when computing elapsed time
• If the latest measurement is more than thirty minutes old, the program prompts the operator to check the sensor
• The config file is validated section by section and key by key, so the message names exactly what is missing or which value is not a number
• PyInstaller packages the application with its icon into an executable that runs on a site PC without a Python installation

Left running on a monitor at the site, the program shows the current temperature and whether it has left the safe range without anyone opening the cloud's web interface. Because a breach announces itself on screen and through sound, the display does not have to be watched.

Thresholds can be changed from within the program, and the sensor being watched, the display window, and the polling interval are all changed by editing the config file — the same executable carries over to another sensor or another site.