Description:

The Pressure Conductive Sheet is made of a material called Velostat. External pressure on the sheet is inversely related to the resistance of the sheet; that is, increased pressure results in decreased resistance. In additional to detecting external forces associated with physical encounters, it is possible to detect respiratory rate using digital low-pass filtering.

Updates:

April 18

We have successfully integrated the pressure conductive sheet into our pouch for the purpose of detecting officer respiratory rate. Shown below is an image of the working sensor.

March 20

Part of our developed algorithm has successfully filtered the respiratory rate signal in live tests to result in relatively smooth curves that can be analyzed in Matlab using a digital 3rd order Butterworth Filter.

Raw signal:

Filtered signal using a third-order low pass filter in Matlab:

Peaks in respiratory cycle detected using Matlab:

March 3

We have successfully build a proof-of-concept sensor for detecting respiratory rate. When hooked up to Alex, we were able to detect fluctuations in signal corresponding to breath rate.

January 22, 2017

Focus on communication with Bluetooth module using digital low pass filter. Low pass filter was written for Arduino for later adaption of processing with phone using open-source and adapted code.

Low pass filter was successfully implemented with ability of Arduino microprocessor to implement digital filter before sending signal to phone, suggesting similar processing can be done once raw data is sent to phone. Currently functional with one module, but multiple module concerns suggest that Arduino RAM space is of utmost importance.

January 14, 2017

• Initial Testing of whole sheet:

<31kohm/cm2 for a 28x28cm sheet

Voltage Divider using 56kohm resistor and Arduino 5V source.

• Issues with signal detection encountered. Reorganize leads to be on opposite sides of the fabric (top/bottom) for better results.

Troubleshoot References:

CS Final Prod

Solutions

Use a layer of aluminum foil to form a conductive sheet on either side of the Velostat. Good for initial prototyping, but not long term solution. Currently using masking tape rather than electrical tape and no soldered wires.

2 primary areas of focus:

• 1×1 piece of conductive film for proof of concept shows success (see attached images) demonstrates pressure sensitive response. (Pressure increases lead to voltage increases)
• Adjust resistor to 6900 ohms
• 1×10 piece of conductive sheet testing. See attached video of breathing. Suggestive of possibility to detect respiratory rate using conductive films.

Future considerations will focus on Bluetooth communication of information to allow for low pass digital filtering of signal in real-time as well as optimization of design.

Future Design Considerations: More reliable conductive sheet and binding material, more consistent electrical contact

Raw Signal Collection

Respiratory Set-Up