Measuring density

For my own memory. A variation of Archimedes' method for digital scales.
We need a beaker of water. We weigh first the object, then the beaker with water, then suspend the object on a string and lower it into the water so that it does not touch anything. The density of water is reasonably accurate unity, so:
Density = weight of object / (weight of beaker with water and object - weight of beaker with water)

Simply weather station on Arduino

Simply weather station on Arduino + BME280 + OLED. Graphs of temperature, pressure and humidity.

The latest version of the sketch is — https://github.com/ruzanow/simply-meteo/blob/master/sketch.ino using the u8g2 library, which supports many displays. In particular: SSD1306, SH1106, HX1230. The library is installed through the arduino environment, Sketch->Connect Library->Manage Libraries. The bme280 library is installed from the same place - a variant from Tyler Glenn.

The assembly is elementary - since the display and the sensor work via I2C, just connect the SDA pins to pin A4 of the arduino, SCK (SCL) to A5, Vin to the 3.3V supply and Gnd to ground.