Sitting for long periods has become more common in today’s jobs causing serious health issues. Unfortunately the plethora of activity trackers fail to address the issue: being rather active while sitting does not provide a good picture of the amount of time spent sitting.
Sit.Up is a simple device that alerts the user if sitting for too long and tracks the sitting time. It comes in two flavours: a device for the chair which works with any user and a device for the user which works with any chair. Currently I am doing some experiments to see which one is more feasible.
This project is an entry for the Hack a day prize 2015 and is a work in progress. Stand by for updates and drop by to give a Skull for appreciation.
25.05.2015 First experiments with chair version
The chair version will work with any user and should be as low cost as possible so that it will be installed on a high scale on any possible chair. Alternatively, if the chairs are dedicated per person they may provide insight on time spend on each chair, like at work, at home or in the car.
I started doing some experiments with an ultrasonic distance sensor. As it turns out, it is not the ideal thing to use: this particular version requires 5V and quie a lot of power, but it will do for the time being, as proof of concept.
The circuit is build around an XMEGA32E5 one some header board, with an attached ESP8266 and your tipical HC-SR04 ultrasonic ranging module, nothing special. It is not optimised for power consumption in any way so it will burn a charge of batteries in 3-4 days. For now, it simply uploads the data to emoncms on my website, similar to Led logger V3.
As it turns out, putting the sensor on the top of the chair is not a good idea: some fabrics seem to be pretty bad at reflecting ultrasounds and crouching does not detect the person.
Next up, i mount this sensor between the seat and back of the chair. It is a delicate position, as a bit higher or lower will cause the sensor to pick up the cushions as obstacles. However this seems to work a lot better, usable with all the types of pants that i have. (well a long wool sweater will still break the thing).
Conclusion on ultrasonic: might work, delicate to place, large. The high voltage and high power consumption may be managed to get decent battery life.
Trying an optical sensor.