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 sensor.
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.
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