MAXREFDES82#: Smart Force Sensor, Load Cell, 2.7 ~ 3.6V in

Technology marches forward, constantly and irrepressibly altering the world of human to devices interfaces. From mobile device touch screens to weigh scales with electrodes for body composition, machines continue to add more capability, and different ways to gather their measurements. Every so often, a truly elegant concept emerges, merging technology, design and simplicity. MAXREFDES82# is one such elegant concept.

This reference design is an industrial, smart force sensor. The design measures mass, as well as the center of mass of the object on it. This combination of features and speed means that MAXREFDES82# operates as both a weigh scale and a touch interface with force sensing. Built with a plastic plate, the system ideally meets the needs of industrial human machine interfaces (HMI).

The reference design features the MAX11254 24-bit, 6-channel, 64ksps 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 center. The force magnitude and coordinates are scanned approximately each 10 milliseconds.

The system includes a thin-film-transistor (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 center.

The MAXREFDES82# reference design consumes minimal energy and is powered by a USB port. A PC-side graphical user interface (GUI) program is also included to facilitate the human interface input demonstration and development.

The MAXREFDES82# reference design block diagram (Figure 1) demonstrates how a touch force and its movement are captured and used in a 3-dimensional (3D) human-interface input device. The design includes source files for the microcontroller to enable developers to quickly 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.