My wife is a physical therapist and asked me to do something like this last week. II came up with something of a 1 point sensor using Velostat, but multiple points like this is ideal. 

One of the first things to pop up in search for something similar was this project. Where did your pcb come from? I understand you designed it but was it made in house or ordered? 

Her application is determining the pressure applied by feet inside a shoe when the patient is told not to bear weight on it due to their condition, and then use that to provide perhaps audio/visual feedback to get them to stop. Something this thin would be perfect inside of a shoe and not really be noticeable to the wearer. I was thinking of having it for use in a clinical application, where it could connect to the local network and log the data so that the clinician can provide real-time feedback to the patient, in addition to the audio visual feedback, such as a rumble motor /or blinky light.

Nick, thanks for your patience - lost track of this post in the end-of-the-term rush.  I used PCBWay for the flex PCB, it set me back a few bucks, but the symmetrical design saved on costs.  I also used them to manufacture the row-scan circuit.

This design works really well, it is both fast and sensitive.  I can scan the 4x4 matrix  under 100us.  My first version was too pressure sensitive and I've had to work on decreasing the sensitivity (shooting for about 10PSI).  The weakness of this design is the velostat itself - it has memory - check out:  Force Sensing Resistor and Evaluation of Technology for Wearable Body Pressure Sensing by Giovanelli and Farella for more detail.  This means that getting an exact pressure value is tricky.  However getting a relative pressure reading is not that hard.

I would be interested in continued work with others on this project.  I think the big missing link is the visualization components.  That is, take the data from the SD card and display it on a PC.  Slapping the analog + 8-bit MCU combo on a daughter board for some WiFi module might be a winning combination.

Nice! I saw those video Marcos did on his yoga mat and figured they'd be useful somehwere along the line. Thanks for entering the Flexible Circuits contest too. Good luck!

Dan, thanks for your feedback.  I was hoping to make a shoe insert for a man's 10.5 (US) running shoe so that I could examine the effect of fatigue, terrain, and slope on my running dynamics over the course of a trail marathon.  My foot has an area of about 200cm^2.  I would need two different flex PCBs to make a pressure sensitive shoe insert - a total of 400cm^2 for a single shoe insert.  Two feet brings this up to 800cm^2.  Yea, this is a big motivator for my entry into this context and yea I know its WAY more than Hack-a-day is offering.  But you'll never get it if you don't ask.