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Intelligent metal detector based on openharmony

2022-07-05 15:49:00 【Openharmony developer community】

be based on OpenHarmony Intelligent metal detector

One 、 brief introduction

Intelligent metal detector is based on OpenAtom OpenHarmony（ hereinafter referred to as “OpenHarmony”） operating system , Use the principle of electromagnetic induction to detect the surrounding metal objects . This example adopts the method of multi device collaboration , compatible OpenHarmony Equipment development and application development , The whole example reflects OpenHarmony Of NAPI、eTS UI、UI Management status @state And audio playback and other technical features .

This project consists of Geek_Lite_Board Development board and Runhe RK3568 Composition of development board ,Geek_Lite_Board The main control chip of the development board is STM32F427IIH6, As the equipment end, detect the change of magnetic field strength , It uses OpenHarmony 3.0 LTS edition . Runhe RK3568 The development board is developed by Runhe software , Using Ruixin micro RK3568 chip , As the application end, it displays metal detection information , It uses OpenHarmony 3.1 Release edition .

Two 、 Running effect

When there is metal around , The buzzer at the equipment end will give an alarm and pass the detection information Wi-Fi The module is sent to the application . After the application receives the detection information , The detection status will be displayed on the screen and the detection results will be announced by voice .

3、 ... and 、 Function realization

Geek_Lite_Board Development board through AK8963 The electronic compass chip obtains the strength of the earth's magnetic field . Usually the magnetic field strength of the earth is 0.4-0.6 gaussian , When the metal is close to the electronic compass chip , According to the principle of electromagnetic induction , The induction of metal in the magnetic field will cause the change of magnetic field signal .Geek_Lite_Board Development board through Wi-Fi And run he RK3568 Development board real-time communication , Upload the detected information in real time . Runhe RK3568 Development board as the application end , Adopt the ark development framework （ArkUI） be based on eTS The extended declarative development paradigm writes pages , adopt NAPI Interface receiving device end Geek_Lite_Board Detection information of development board , Use OpenHarmony The audio playback function in the media subsystem realizes voice broadcast of metal detection status .

Magnetic field data acquisition

AK8963 A three-axis electronic compass integrated chip with high sensitivity Hall sensor technology , The interior contains magnetic sensors , Can be in x Axis 、y Axis 、z The axis detects the strength of the earth's magnetic field .

● adopt Mpu_Read_Bytes() Function reads the value of the chip data register .

uint8_t Mpu_Read_Bytes(uint8_t const regAddr, uint8_t *pData, uint8_t len)

● obtain AK8963 Magnetic field raw data .

Mpu_Data.mag_x = (MPU_BUFF[16] << 8) | MPU_BUFF[15]; // x Axial magnetic field data Mpu_Data.mag_y = (MPU_BUFF[18] << 8) | MPU_BUFF[17]; // y Axial magnetic field data Mpu_Data.mag_z = (MPU_BUFF[20] << 8) | MPU_BUFF[19]; // z Axial magnetic field data

● Yes AK8963 Transform the original magnetic field data , Get the magnetic field strength , Unit Gauss .

Gauss_Mag_z = Mpu_Calc.mag_z * 0.15f * 0.01f;

Detect metal information

First collect 100 Group z Axis magnetic field strength reference data , Then average these data , From this we can get z Zero point data of axial magnetic field strength .

const uint16_t calibrateCount = 1000; //  The maximum number of measurements is 1000const uint16_t calibrateFrequency = 5; //  Every measurement 5 Take one valid value at a time const uint16_t calibrateAverageCount = 100; //  take 100 Secondary valid value if(i < calibrateCount){    i++;    if(i%calibrateFrequency == calibrateFrequency){       Mag_z_buff[j++] = Gauss_Mag_z;        if(j >= calibrateAverageCount){            i = calibrateCount;            Mag_z_Flag = true;            for(k=0;k<calibrateAverageCount;k++){                origin_mag_z += Mag_z_buff[k];            }            origin_mag_z = origin_mag_z / calibrateAverageCount;            //  Calibration complete , The blue light is on , Send to the application  "CalibrateOK"            BLUE_LED_ON();            memset(buff,0x00,sizeof(buff));            sprintf(buff,"angle:%s","CalibrateOK");            ESP8266_send_data(buff,strlen(buff));        }    }}

With origin_mag_z As zero point , Compare the obtained magnetic field data with it , To judge whether metal is detected .

NAPI get data

NAPI（Native API） yes OpenHarmony A kind of standard system JS API Implementation mechanism , Suitable for packaging IO、CPU intensive 、OS The bottom layer and other capabilities are exposed JS Interface , adopt NAPI Can achieve JS And C/C++ Code accesses each other . Runhe RK3568 The application end passes through NAPI To receive the detection information sent by the device .

● Bottom NAPI Module encapsulation

The package module is named tcpserverapi, Download to tcpservermodule Folder .

Download it and put it in 3.1Release Source root , And configure the compilation script ; After the first compilation, you need to burn the entire image , Later, modify the module source code , Just put the Library send Go inside the board . The order is as follows ：

//  First mount , Again sendhdc_std shell mount -oremount,rw /   hdc_std file send libtcpserverapi.z.so system/lib/module/libtcpserverapi.z.so

● Application side import NAPI modular

import tcpserverapi from '@ohos.tcpserverapi'

● Application end NAPI Interface call

//  call initServer Interface   initialization  TCP  The server tcpserverapi.initServer() //  call recvMsg  Get and parse Geek_Lite_Board The angle sent from the development board tcpserverapi.recvMsg().then((result) => {      var resultAngle = result.angle;})

UI Status display and management

As shown in the above figure, the page under detection , The overall layout is divided into text title and detection status diagram .

The text title is composed of Flex Layout container text Component implementation , Used to present a piece of information , The following for text Interface related properties .

● The detection state diagram includes the page background diagram , Detection state diagram , Test result description , The specific functions are Flex Flexible layout component implementation . The interface prototype is shown below ：

Flex(options?: { direction?: FlexDirection, wrap?: FlexWrap, justifyContent?: FlexAlign, alignItems?: ItemAlign, alignContent?: FlexAlign })

● By calling recvMsg The interface picks up the message of the metal detector , And modify the display status of the home page , The key implementation code is described as follows ：

aboutToAppear() {    var intervalID = setInterval(() => {        tcpserverapi.recvMsg().then((result) => {       }   }}

among “ var intervalID = setInterval(() => ” Timer used , Timed call “recvMsg” Method , adopt NAPI Obtain metal test results .

if (resultMetal.match("metal:")) {    this.metal = resultMetal.slice(6);    console.info('=======' + this.metal)    if (this.metal === 'Detected') {          this.detectionState = ' Find metal ';          this.detection = $r("app.media.img_detected");          this.isDisplay = false;    }    else if (this.metal === 'UnDetected' || this.metal ==='CalibrateOK') {          this.detectionState = ' Testing ';          this.detection = $r("app.media.img_detecting");          this.isDisplay = true;     }}

When passed NAPI The detection information obtained by the method is “ metal:Detected ” when , Set up detectionState To discover the state of metal , The screen shows that a metal page has been detected ; When passed NAPI The detection information obtained by the method is “ metal:UnDetected ” when , No metal information is detected at this time , Set up detectionState Is in the detection state , The screen displays the detection status page .

Voice broadcast detection status

When metal is detected ,RK3568 The voice message that metal has been detected will be broadcast , Achieve the purpose of notifying users , adopt OpenHarmony The audio playing function of the media subsystem is realized .

OpenHarmony The media subsystem provides developers with a simple and easy to understand interface , So that developers can easily access the system and use the media resources of the system . The media subsystem includes audio playback 、 Video playback 、 Common functions such as audio recording and video recording .

The main work of audio playback is to transcode audio data into audible audio analog signals and play them through output devices , At the same time, manage the playback task . This example mainly imports media modular 、 Create an audio playback instance 、 Realize the audio playback interface and the pause playback interface .

● Import media modular

import media from '@ohos.multimedia.media';

● Create an audio playback instance

// OH media object private player = media.createAudioPlayer();

● Realize the audio playback interface

Use play() Call to start playing audio resources , After the audio data is loaded , namely src Property setting is completed before calling .

play():void

Four 、 summary

This article briefly describes how to use OpenHarmony Develop multiple devices , Demonstrated NAPI、eTS UI、UI Management status @state And the application of technical features such as audio playback , Through these diversified functions , We finally implemented a sample metal detector . Rich and varied OpenHarmony Developing samples is inseparable from the contributions of partners and developers , If you want to share your own examples , Welcome to submit the sample to OpenHarmony Knowledge system SIG Canglai , Work together to build development samples .