Barlow test

The most common problem with cheap glues is the actual crooked glue itself, which gives a traffic light output (transverse chromatism). The problem can be seen by both the (artificial) star and the displaced Newton rings. The ring test is faster and should be done this way: take a green laser pointer with a diffuser (matte plastic or a couple of cloths) and by tilting the pointer, find the position where the rings are visible. It is advisable to do this in a dark room because the rings are quite faint. Normal barlow will have the rings in the center. On the left the normal, on the right the curved glue:

However, you can try to use the latter as an ADC by turning it to a position where it reduces atmospheric dispersion.

Starcalc

A bit of an antique. The good old starcalcafter installing some other software in the system, there was a problem with closing (and saving the settings). After some troubleshooting it turned out that before the hang it sends a global SendMessage and some software won't respond. The solution is obvious - change SendMessage to PostMessage, not waiting for a response. You need to replace byte D9 with 69 at address 9887B.

And the whole folder starcalc, with plugins — https://disk.yandex.ru/d/HL4pO27CZy4eiQ

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.