Based on our everyday interactions with satellites — e.g. GPS, satellite TV, Internet — we have some vague sense that these devices are out there, floating around and providing the world with useful information. But how many are there, and are there any actually above you right now? The answer to the first question, based on this listing on celstrak.org, is more than 7,500.
To answer the second question, Okubo Heavy Industries built an overhead satellite detector, as a “campy bit of Arduino spy-tech theater [which] actually works.” It features a QT Py board for processing, along with a BN-280 GPS unit to determine the user’s position on the surface of the earth, and to get the current time.
The location of satellites is determined via data from the celstrak list stored an SD card. The QT Py board cycles through each satellite’s position in space and compares it with current GPS data. It then alerts you if any satellite is more than 70 degrees above the horizon via its dual-SSD1306 OLED screen user interface. One screen displays position information, while the other shows the location on a world map, as well as the satellite’s orbital path.
The entire setup is constructed on two small breadboards, and is powered through the QT Py's USB connection. You can see it demonstrated via a short video on the project's Reddit post, while code for the build is available on GitHub.