Pressure ulcers are wounds that arise when a person sits or lays in the same posture for an extended period of time. Starting from the skin and possibly continuing to the bone, tissue slowly decays when the pressure keeps being applied to the same spot. Prevention is the best method of treating the ulcers and it is done by regularly changing posture. Normally a person does this automatically but for a portion of hospital patients this option is not there.

The goal of this project was to design and create a prototype which can track the body position of a person on a bed. This way an alarm can be triggered when a person stays in the same body position for too long. To complete this goal a list of requirements was created to guide the design process. The most import design requirement was the ability to track the body position non-intrusively, which means a person should not perceive the tracker in any way. Furthermore, minimizing cost and interference were also important design considerations.

Using piezoelectric and piezoresistive sensors beneath a mattress, the pressure a person applies to it can be measured and used to determine the body position. The sensor encasing is thin enough to go unnoticed through the mattress when lied upon. Therefore, the non-intrusive tracking is successfully implemented.

By keeping the circuitry simple and looking for the most cost-effective components the overall costs for the entire electrical system are kept to a reasonable minimum. For the piezoelectric circuit a parallel zener diode was all that was necessary and the piezoresistive circuit consists of an inverting amplifier and low-pass filter. The cost per system comes down to $€146.39$, which can still decrease when a more tailor-made microcontroller is used for reading out the analog-to-digital converters and when costs decrease due to buying in bulk.

Minimizing the interference for the system is implemented to some degree for the piezoresistive by adding a low-pass filter before the ADC input. The lack of physical shielding results in a poor interference reduction. This will have to be addressed in the future.

The required cooperation within the project resulted in many prototypes being developed to ensure the algorithm could use the most recent version of the system at any time. The collaboration with a mechanical engineering student resulted in an integrated prototype of both mechanical and electrical design.

The additional targets set for the project consisted of detecting respiration rate and heart rate, creating a PCB and creating a pilot worthy prototype. Of these targets the PCB creation is the only target which is nearly completed. Soldering the PCB can however not be done before completing this report due to delivery times.