“Starting playing with Arduino seems simple enough. You can find all sorts of tutorials, instructables, wiring and code examples for pretty much every sensor, component, or module available. So far so good. But when the time comes for building a more complex device, the troubles start. The tutorials for adding multiple modules to Arduino and then working with them efficiently are very scarce. Therefore, with this instructable, I will try to help with just that. So here comes the Arduino thermometer/hygrometer with a GUI, designed to push Arduino to its limits. A small confession is in order though. When I started this project, I thought that the limit to it were the number of Arduino GPIOs, which limit the number of modules one can attach to it. I was considering multiple sensors, more than one display, several buttons and other input modules. However, as I later discovered, the real bottleneck proved to be the limited memory (firstly RAM, but Flash comes a close second). So I shrunk down the project quite a lot, but I ended up with a nice (and hopefully someone will share this sentiment with me) and quite feature rich thermometer. The whole journey made me think that the experience should be shared with the community, since Instructables helped me a lot with my first steps in Arduino. The project is based on an OLED display, a small pot-based joystick, and temperature and humidity sensor (thermometer/hygrometer). It is designed to connect to an external thermometer/hygrometer over the built-in UART. Analog and digital inputs, and digital outputs are used, eeprom, timers, and interrupts. A small programming framework is provided, which lets one add and remove sensors with very little programming.”