Intelligent metal detector based on openharmony

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 1000
const 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  &quot;CalibrateOK&quot;
 BLUE_LED_ON();
 memset(buff,0x00,sizeof(buff));
 sprintf(buff,&quot;angle:%s&quot;,&quot;CalibrateOK&quot;);
 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 send
hdc_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 .

5、 ... and 、 Reference link

RK3568 Develop the silky experience on the board OpenHarmony Standard system

https://gitee.com/openharmony-sig/knowledge_demo_smart_home/tree/master/dev/docs/rk3568_quick_start

stay Windows compile OpenHarmony engineering

https://gitee.com/Cruise2019/team_x/blob/master/homework/ohos_build_win/readme.md

OpenHarmony NAPI  Learning documents

https://gitee.com/javen678/hello-ohos-napi/tree/master/doc#/javen678/hello-ohos-napi/blob/master/doc/1.HelloNAPI.md

OpenHarmony be based on eTS Extended declarative development paradigm

https://gitee.com/openharmony/docs/blob/master/zh-cn/application-dev/reference/arkui-ts/Readme-CN.md

Audio playback development guide

https://gitee.com/openharmony/docs/blob/master/zh-cn/application-dev/media/audio-playback.md

Develop metal detector applications from zero

https://gitee.com/openharmony-sig/knowledge_demo_temp/blob/master/docs/metal_detection/quick_develop.md

GEEKROS Official website

https://www.geekros.com/