Yoga Mat-Size Pressure Sensor Matrix Uses LattePanda and Velostat to Save Money

Scale is, of course, one of the largest contributing factors when it comes to the overall cost of a project. A single LED, for example, costs just pennies. But if your project requires thousands of them, the cost of the BOM quickly becomes overwhelming.

Marco Reps ran into this problem when he wanted to create a large pressure sensor matrix. While traditional force-sensitive resistors work well, they still cost a dollar or two each when purchased in bulk. Marco’s project was intended to be human scale (roughly the size of a yoga mat), and to achieve a decent resolution he would have needed 10,000+ of those resistors, which would have been prohibitively expensive.

The solution he came up with was to use Velostat, which is a conductive material that’s resistance changes as it is compressed. Putting a layer of Velostat between two layers of copper allowed him to accurately measure the pressure being put on the mat. To get a high-resolution image of that pressure, he divided the mat into 1cm² individual units.

But, as you might expect, actually measuring that many units became a challenge in itself. The mat required 10,800 units (180 x 60 resolution). To gather the data from all of them, Marco used a LattePanda and multiplexers. The operation works a lot like an LED matrix, with only a handful of pins shifting through the entire range of inputs.

All of those inputs required some sort of visualization too, and luckily the LattePanda was able to handle that as well. Each unit’s resistance is measured, and the software then changes the color of the corresponding square in the visualization. As more pressure is applied, the color shifts from blue to red. The result is a high-resolution, human-size pressure mat at an affordable cost.