NEC Yamanashi MR and Renesas MCU smart water meter solution

chrispeng December 29, 2021 industry

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Although the current domestic water meter market is still dominated by mechanical watches, from a development perspective, intelligence is an inevitable trend. It can save labor, improve the accuracy of meter reading, and can realize stepped charging, effectively using limited water resources.

The power supply of the water meter is generally supplied by the water meter itself, which puts strict requirements on the power consumption of the water meter. According to international regulations, the quiescent current of a smart water meter should be less than 30μA. Actually, water meter manufacturers control this indicator within 10μA (when using a reed switch sensor), and ensure that the working time is more than 6 years before it is qualified. NEC’s 8-bit microcontroller with LCD control function has become a high-quality choice for water meter microcontrollers due to its advantages of low power consumption and high performance.

The working principle of the NEC Yamanashi MR and Renesas MCU water meter solutions is as follows: a magnet is installed on the impeller, and the rotation of the impeller is sensed by the magnetic field sensor (MR Sensor). The magnetic field sensor (MR Sensor) converts the magnetic field signal into an electrical signal, and then adds or subtracts the measurement by the single-chip microcomputer, and the calculated value is displayed on the liquid crystal or output to the outside.

figure 1

The block diagram of the program structure is as follows:

Figure 2 Renesas (formerly NEC) water meter scheme structure block diagram

　　Renesas MCU-78K0/Lx3 microcontroller introduction

Renesas Electronics 78K0/Lx3 microcontrollers are high-performance 8-bit general-purpose microcontrollers, using the original NEC Electronics 78K0 core, in a variety of packages from 48Pin to 80Pin, built-in 4Com/8Com mode LCD driver, and the number of LCD segments that can be driven is up to Segment 288.

LCD driver

A maximum of 36*8 segment control can be achieved, with a total of 6 display modes for selection, internal/external grouping voltage.

CSI communication module 1~2

Can communicate with IC card receivers, short-range wireless transceivers, and ultrasonic flow sensors

Rich comparison/trigger timer

Collect the flow sensor signal and accurately calculate the flow rate

EEPROM emulation function

Use flash data programming and special management methods instead of EEPROM to store important data

Oscillation circuit

The 78K0/Lx3 microcontroller has a built-in high-precision 8MHz oscillator circuit, and can control the speed of the internal oscillator circuit through registers. For water meters that do not require a real-time clock, costs can be saved and the software development progress can be accelerated. If you need to use RTC, you need to connect an external 32.768kHz oscillator, which can easily realize the multi-rate water tariff.

Power consumption

The static power consumption of 78K0/Lx3 less than 1μA can effectively extend the battery life and help improve the stability and anti-interference of the system. The working voltage of 1.8V～5.5V can maximize the use of battery energy. The built-in 16-level LVI module eliminates the worries of customers. It monitors the battery voltage at any time. Once the battery voltage drops over the limit, it will immediately notify the user and store key data. The NEC electronic water meter solution is a card meter solution, which supports a variety of read-write cards, and communicates with the microcontroller through the card socket using the IIC protocol. The microcontroller uses 78K0/Lx3 with LCD display control function. In terms of power consumption, through various power-saving measures, the whole machine achieves an ultra-low power consumption of 3.8μA.

　　NEC Yamanashi MR sensor

NEC Yamanashi’s MR magnetic sensor is a magnetic switching device that uses the principle of magnetoresistance reaction to vapor-deposit a ferromagnetic metal alloy film on the IC circuit. Its characteristics are:

High sensitivity, high precision-the consistency of sensitivity can be as high as 6 Gauss or less.

High reliability-Built-in temperature protection circuit greatly improves the stability of temperature characteristics.

Low power consumption-working current 1.5mA, working in pulse mode, the average power consumption can be reduced to 0.45uA.

low cost.

Small package.

Compared with a variety of different sensing devices:

Table 1 Comparison table of induction devices

NEC Yamanashi MR sensor application program in water meters Magnetic sensors are suitable for speed water meters, which can be divided into rotor type and wing type. The magnetic field distribution is different, and there are corresponding magnetic sensors.

Case 1: Horizontal direction detection