Sensors

Sensors are a core component in devices that are used for weight measurements.  They are needed to detect the amount of direct force that a subject exerts in a downward direction, which can be translated into weight.  In this project it is desirable for the weight reading to be very accurate so that any slight change in behavior can be tracked through weight change.  The final design is accurate within ± .2 lbs, which is the same as most higher-end bathroom scales.

An important performance specification of the In-Shoe Force Sensor is its power consumption and battery lifetime. For convenience and practicality, the battery should be able to provide reliable weight readings over the course of a day. In order to ensure this design criterion was accomplished in the final product, it was necessary to first identify how many times the average product user would request their weight in a normal day of operation, then determine if the power source selected could provide the determined power demand. Performance factors that were considered are power draw profile, maximum lifetime, end of lifetime sensor performance, and end of lifetime communication performance.

One of the most important subsystems of the In Shoe Weight Sensor project involved developing a mobile application that is suitable for an Android or iOS platform. The specs for this portion of the project were to design an application where users are to be able to request a weight reading from the hardware which will then interpreted by the Arduino and the collected information is presented to the user in a simple but efficient manner.

The smartphone application needs to be able to communicate with the sensors installed in the shoe soles and vice versa. As noted in the high level description of our FAST diagram, the phone to sensor communication will be handled via Bluetooth.

The module is equipped with a Transmit (Tx) and Receive (Rx) pin, which allows it to be able to send and receive data. The module will be connected to an Arduino microcontroller that will act as an interface to handle the sensor-to-Bluetooth module communication but also the Android application-to-Bluetooth module communication.