SLAA220A November 2004 – August 2018 MSP430F423 , MSP430F423 , MSP430F423A , MSP430F423A , MSP430F425 , MSP430F425 , MSP430F425A , MSP430F425A , MSP430F427 , MSP430F427 , MSP430F427A , MSP430F427A
This application report describes how to implement a single-chip pocket weight scale using a resistive full-bridge sensor and a fully integrated MCU solution using low-power design practices. The included software obtains the measurement results using the MSP430™ on-chip sigma-delta analog-to-digital converter (ADC) and displays them on an LCD. A 3-V battery powers the portable device. The design includes a two-point calibration mechanism for offset and gain calibration. The sample code described in this document can be downloaded from www.ti.com/lit/zip/SLAA220.
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Applications for weight, force, torque, and pressure measurement frequently use resistive full-bridge sensors. Most of the bridge sensors require a high excitation voltage (typically in the 10-V range) and output a low full-scale differential voltage in the range of 2-mV/V excitation voltage. The output from the sensor is typically amplified by an instrumentation amplifier. After signal conditioning, the signal is digitized by a high-resolution ADC. Typically, such high-resolution ADCs are not integrated in conventional microcontrollers (MCUs). A general-purpose MCU is then used for further processing and display.
The conventional approach of using a bridge sensor excitation voltage of 10 V and an Instrumentation amplifier to achieve a full-scale ADC input voltage increases chip count and complexity of power management with high power consumption. An energy-efficient and cost-effective solution is to use a microcontroller with an integrated high-resolution ADC and an integrated programmable gain amplifier (PGA). The entire application can then be powered from a 3-V battery. The MSP430F427A microcontroller (MCU) has integrated 16-bit sigma delta ADCs with differential inputs and PGA with gain up to 32. This device offers a single-chip solution for this application that includes not only high-resolution ADCs with PGA but also an LCD driver and brownout protection.