1. Introduction to the MSP430FW42x Microcontroller The MSP430FW42x series microcontrollers are dedicated MCU chips developed by TI for electronic flow and rotational motion detection. They perfectly combine an ultra-low-power MCU, a rotary scanning interface (SCAN IF), and an LCD driver module. The device's ultra-low-power architecture and flow detection module not only extend battery life but also improve the accuracy and performance of the instrument. Typical applications of the MSP430FW42x include heat meters, hot and cold water meters, gas meters and industrial flow meters, anemometers, and other rotational detection applications. 2. Principle of Flow Measurement 2.1 Basic Principle A mechanical device consisting of an impeller or helical gear converts fluid flow into rotation, enabling the measurement of fluid flow rate. Placing an inductor in a resonant circuit above the impeller detects its rotation. Half of the impeller is coated with copper or other damping metal. The damping coefficient of the resonant circuit is determined by the position of the inductor above the impeller. When the inductor is in region a, the damping coefficient of the circuit is higher than when the inductor is in region b. By measuring different damping coefficients of the resonant circuit, rotation can be measured. Figure 1 shows a schematic diagram of the measurement principle. 2.2 Oscillation Test Method Figure 2 shows the oscillation waveforms when the two sensors are in different regions. The MSP430FW42x uses the oscillation test method to convert different attenuation amplitudes into digital signals for measurement. In this method, the attenuation coefficient of sensor 1 in Figure 2 is represented as L, and the attenuation coefficient of sensor 2 is represented as H. 2.3 Signal Processing As the impeller rotates, the signals of sensor 1 and sensor 2 change continuously. Figure 3 shows the state changes of the two sensors. If the previous state and the new state are known, the direction of rotation can be determined simultaneously. Increment: from state d to state a; Decrease: from state b to state a. 3. Non-magnetic Water Meter Design Using MSP430FW427 The water meter designed using the MSP430FW427 has a very simple circuit structure. The flow measurement part is completed by the built-in SCAN IF module of the MSP430FW427. Figure 4 shows the principle block diagram of the non-magnetic water meter system designed using the MSP430FW427. 4. SCAN IF Module Design The SCAN IF module can automatically detect linear or rotational motion with low power consumption. As shown in Figure 5, the SCAN IF module consists of three parts: Analog Front End (AFE), Signal Processing State Machine (PSM), and Timing State Machine (TSM). The analog front end excites the sensor, detects the signal, and converts the signal into digital form; these digital signals enter the signal processing state machine, which analyzes and counts the rotational motion based on these signals; the timing state machine controls the analog front end and the signal processing state machine. [align=center] [/align] The settings for the SCAN IF module during software development are as follows: (1) Basic settings of SCAN IF ◇ Set the control registers SIFCTL1, SIFCTL2, SIFCTL3, SIFCTL4 and SIFCTL5 of SCAN IF; ◇ Define the P6.x/SIFCH.x pin as the function of the SCAN IF module; ◇ Turn on the “VCC/2” generator; ◇ Select the clock source; ◇ Signal state processor. (2) Planning the time state machine The time state machine of SCAN IF is used to determine the measurement sequence. The time required for each step can be precisely adjusted. The typical measurement sequence is: determine the idle state; excite the LC sensor; delay for a certain time, at which time the measurement can be performed; turn on the DAC and comparator; measure; stop. (3) Defining the hysteresis threshold of the DAC The DAC provides a hysteresis threshold for the damped and undamped oscillators of each sensor. The hysteresis threshold of the DAC is adjusted by observing the oscillation curve of each sensor and the voltage of the DAC. (4) Signal Processing State Machine: The signal processing state machine is a designable state machine that obtains the rotational speed and direction through the state table stored in the MSP430 memory. The vector SIFTPSMV initially points to the state table of PSM. 5. Example of SCAN IF Module Initialization Program 6. Conclusion: This paper introduces the working principle of flow measurement using the LC oscillation test method, and successfully designed a non-magnetic water meter based on the MSP430FW427 based on this principle. Since the SCAN IF module is very flexible in its settings, designers can set it reasonably according to their actual situation. The other integrated peripherals and ultra-low power consumption operation capabilities of the MSP430FW427 microcontroller also enable us to develop advanced instruments.