Maxim Integrated has posted details of its Reference Design MAXREFDES82#, for a sensor configuration that measures mass, as well as the centre of mass of the object on it. This combination of features and speed means that the design operates as both a weigh scale and a touch interface with force sensing.
Built with a plastic plate, the system meets the needs of industrial human machine interfaces (HMIs). The design features the MAX11254 24-bit, 6-channel, 64 ksample/sec delta-sigma ADC with SPI interface. Four load cells are mounted on a quadrant plane to detect touch forces applied on the flat plastic plate. Based on the forces applied on each individual load cell, the system displays the total force magnitude, and the coordinates of the force centre. The force magnitude and coordinates are scanned approximately each 10 milliseconds.

The system includes a TFT liquid crystal display (LCD) module, digitally showing the forces on each individual load cell, and the total force applied on the top plate. The LCD module also graphically displays the force magnitude and the coordinates of the force centre. The design is low power and is supplied by a USB port. A PC-side GUI program is also included to facilitate the human interface input demonstration and development.
The block diagram demonstrates how a touch force and its movement are captured and used in a 3-dimensional human-interface input device. The design includes source files for the microcontroller to enable developers to evaluate and customize the design for their specific applications with minimal firmware or hardware changes. The board is designed in a compact form factor for rapid evaluation or installation.