ATtiny85 Sitting-Too-Long Alarm
Dave Bennett's smart chair cushion tells you when when you need to stand up.
If you work sitting down – or perhaps even more so if you're an avid gamer – you may find yourself on your posterior for hours on end. Dave Bennett found himself in the sitting position for much too long, and while his smartwatch can tell him when to get up, it’s all to make that notification go away. Another solution was needed, which he took care of with his new ATtiny85-augmented cushion.
The new device sits on Bennett’s chair, and uses a layer of Velostat as a force-sensitive resistor. When he sits down, the Velostat is compressed, lowering the resistance between layers of copper tape on either side. This variable resistor setup is put in series with a fixed resistor, and the input is then picked up with the help of a comparator. The comparator signal is fed into an ATtiny85, which sounds the alarm as needed via a transistor.
Programming-wise, the ATtiny goes to sleep and wakes up every eight seconds to determine Bennett’s stand/sitting state. If 255 sit indications are recorded in a row (225 measurements x 8 seconds = 18,00 seconds = 30 minutes) the system repeatedly beeps at him. Using a sleep routine here should allow this ATtiny85-based project to run via a battery for quite some time.
As shown at around the 3:30 mark, the alarm is pretty annoying, though that's the point. It's a useful build, which shows off a few concepts that could easily be applied to other projects as well. The schematic, along with code and other details, is available on GitHub.