12.07.2015 E-filed sensor

A project log for Sit.Up

Sitting for long periods has become more common in today’s life causing serious health issues. Sit.Up!

electrobobelectrobob 08/11/2015 at 21:540 Comments

As my initial capacitive sensor using aluminium tape as electrodes proved successful, I looked into shrinking the size. Compared to measuring the capacitance, another method of detecting a conductive object like the human body around a sensor is by using the electric field method: 2 electrodes form a transmitter and receiver. When a conductive body comes between them, the amount of signal received changes. I have attempted to use a 75x100mm double sided PCB for this method, at first. In open air the detection distance can be even 20cm, but things change once this plate is placed under a chair: the sensor is very directional and there are ways to sit on the chair without being detected. Swapping the PCB for the original aluminium tape electrodes works better, but there is no point of implementing this method, as it requires extra parts. The system in this case consists of the microcontroller outputting a 1MHz signal on a pin serving connected to the transmitter electrode while the other electrode, the receiver, gets read out by the microcontroller’s ADC after passing through a simple detector.