Predicting periodic events with FFT

Problem description

We have embedded devices periodically sending us data. We want to be alerted as early as possible when a device stops sending data.

A very simple approach is to take the time difference of the last few times a device sent data and calculate the average. When we know a device sends data roughly every 15 minutes, we can easily trigger an alarm if no data arrived for that time.

The above approach assumes devices send data with the same period always. However, that is unfortunately not true for all. We have found devices which never send data during the night. Or devices which stop sending every afternoon, presumably because their GSM internet connection becomes disturbed. Continue reading “Predicting periodic events with FFT”

Bogenschieß-Ziel

Die Kinder interessieren sich mehr und mehr fürs Bogenschießen und brauchen passende Ziele. Naturgemäß sind Zielscheiben, die der Papa irgendwo hinstellt, langweilig. Dazu muss gesagt werden, dass wir natürlich nur Pfeile mit stumpfer Gummispitze haben, alles andere wäre zu gefährlich.
Aber was nimmt man als perfektes, ethisch korrektes Ziel?  Continue reading “Bogenschieß-Ziel”

Weather monitor

The basic idea of the weathermon project is to obtain, record and monitor the weather at my home. All weather data is sent from wireless sensors and then stored in a database, from which different graphs are generated that can be viewed on a PC, over the Internet and on a smartphone. Continue reading “Weather monitor”