While I was working with my father in his cargo transport firm “Ima me svuda”, we acquired a temperature-controlled refrigerator car for transporting perishable goods such as food and medicine supplies. After some time, the government introduced a regulation that all perishable goods transported via refrigerator cars must have their temperature monitored for the whole length of the transport. The recipient is then obliged to check the monitor logs and see if the temperature was appropriate for the type of the goods, and that it was constant during the transportation.
This meant that we had to buy a temperature monitor and install it into our refrigerator car. The prices were way too high for us to even consider buying, so we decided to build our own.
The idea was to create a temperature monitor that will be mounted in the cargo area and be powered by batteries or by the car’s 12V power supply. Temperature data will be stored in an SD card and it would be sampled on 10 seconds. When we needed to present the temperature data, the SD card would be put into the USB case and plugged into any PC. A custom script located on the SD card, when run, would read the temperature data and draw the graph of temperature transition over time. The script is fully independent and requires nothing from the host OS (only that it is Windows, but all PCs we ever encountered were running Windows).
The whole project is stored and documented on the Sourcehut page.
Sadly, the whole refrigerator car engagement didn’t last long after we created the custom monitor, so it didn’t see much use in the field.