Development of digital medical weight scale using 32-bit arm based microcontroller

This thesis includes the design and implementation of a modern digital weighing medical scale. The system includes facilities for interactive connection feature with smartphone which makes the scale to be used as daily body fitness and patient weight monitoring system. The weighing scale is of small size, strong, low power consumption and it has been built to be suitable for professional medical environment. Stain was used as an electric transducer to convert the weight into an electrical signal. The strain gauge was applied within Wheatstone bridge. On no load condition the bridge was adjusted to be in balance condition. When a load was placed on the scale, the bridge become resistance of the strain gauge according to the weight placed on the scale. This unbalanced was created output voltage at the output terminals of the bridge a low noise instrumentation amplifier (LNIA),which can amplify low level signals even with existence of high common mode rejection ratio, high input impedance and high gain . By using this amplifier, the common noise and temperature dc drift were cancelled and only the differential signal was amplified with gain of 128db. The output of the amplifier was converted into a digital data using 24analogue to digital converter ADC. A medium density performance line ARM based, 32 bit,72 MHZ microcontroller unit (MCU) was used to control the operation of the weighing scale. The processing the output signal of the ADC was achieved by MCU using a software program which was designed for this purpose. A Standalone liquid crystal diode (LCD) display was used to display the weight value. A Bluetooth radio was implemented to send weight data on line to the smartphones for continuous monitoring of the data bus medical staff. All the purposes several tests were carried out on the system to measure the accuracy and resolution of the scale. The maximum error of the weight scale was 0.3 Kg in 200Kg weight