Disclosure: I'm affiliated with aquariumpet.co.uk, a UK shop that sells aquarium heaters. An aquarium heater's display tells you what the water is doing right now , near the rod. It doesn't tell you what happened at 3 a.m., whether the far end of the tank lags behind, or how long the heater actually runs each day. For that you need a log. This tutorial builds a small, independent temperature logger with a Raspberry Pi and a DS18B20 sensor. It writes a CSV and warns you when the temperature ...