Pressure Sensor and IMU testing

Tekscan Sensor Testing

Four Tekscan A401 pressure sensors were ordered at a cost of $150 USD. These sensors will be arranged in the GaitKeeper insole to detect changes in gait patterns (along with the IMU), to help characterize fall risk.

The sensor conductance varies with perpendicular force applied to the sensing area, shown below.

The Tekscan electrical integration guide recommends several approaches, one of which is a voltage divider, shown below.

This circuit was created on a breadboard with an Arduino MEGA providing a 5V reference and 10 bit ADC. Various values for R1 were tried and various weights were placed on the pressure sensor, culminating with Luke Morabito concentrating his entire body weight on a single sensor. It was experimentally determined that R1 = 2.2kOhm mapped a weight of 0-160lb to 0-4V, demonstrating that the Tekscan sensor was able to measure forces at the desired range and precision.

Once the first prototype is complete and the four Tekscan sensors are integrated with the Adafruit nRF52 board, the sensors need to be properly calibrated with a set of reference weights up to a reasonable maximum human weight.

MPU6050 IMU Testing

The MPU6050 development board consists of a 3-axis accelerometer for detecting linear acceleration, and a 3-axis gyroscope for detecting rotational velocity. Numerical integration and interpolation will be applied to this raw data in the cloud, then gait characteristics can be determined. As an initial test, the MPU6050 is connected to an Arduino MEGA via I2C, and data collection abilities are verified.