目錄

• • • • ADC觸摸檢測原理
      • ADC的使用
      • 觸摸檢測程序設(shè)計(jì)

ADC觸摸檢測原理

??ADC內(nèi)部電容Chold與外部引腳所接電容Csensor并聯(lián)，等效電容為二者之和。首先將內(nèi)部電容Chold充電，將外接電容Csensor放電，然后連接二者，將二者電荷量Q保持為恒定值。根據(jù)電容公式 Q = CU 可知，當(dāng)手觸摸外部電容Csensor導(dǎo)致其電容增大時(shí)，等效電容隨之增大，而電荷量Q恒定所以電壓U下降。測量得出觸摸與未觸摸時(shí)電壓的閾值后就可以根據(jù)電壓變化來判斷是否觸摸。

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ADC的使用

1、引腳PORT配置

TRISx寄存器控制引腳數(shù)據(jù)傳輸方向，ANSELx寄存器控制引腳數(shù)據(jù)類型為模擬信號還是數(shù)字信號。

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2、CHANNEL 選擇

ADPCH寄存器決定channel。

注意，在改變channel后要delay一會(huì)兒才能開始下一次轉(zhuǎn)換。

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3、選取參考電壓

ADREF的ADPREF位選擇正參考電壓，ADREF的ADNREF位選擇負(fù)參考電位。

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4、CLOCK 選擇

通過ADCON0寄存器的ADCS位和ADCLK寄存器來選擇。

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5、輸出格式控制

ADC轉(zhuǎn)換結(jié)果保存為10bit數(shù)據(jù)存入ADRES，有兩種對齊方式，ADCON0的ADFRM0位決定result的左 / 右對齊。

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6、開啟ADC

把ADCON0的ADON位置1

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7、預(yù)充電和采樣

只有外接電容，使用CVD方法實(shí)現(xiàn)觸摸檢測時(shí)才進(jìn)行預(yù)充電，作用是對Chold和Csensor充/放電，但是僅僅是進(jìn)行AD轉(zhuǎn)換則不需要預(yù)充電。可通過ADPRE寄存器控制預(yù)充電時(shí)長。采樣是在AD轉(zhuǎn)換之前進(jìn)行的，時(shí)長由ADACQ寄存器設(shè)置。必須等待采樣結(jié)束才能開始AD轉(zhuǎn)換。

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8、開啟AD轉(zhuǎn)換

把ADCON0的ADGO位置1時(shí)開啟AD轉(zhuǎn)換，轉(zhuǎn)換結(jié)束時(shí)ADGO自動(dòng)清0。應(yīng)當(dāng)循環(huán)或者定時(shí)判斷ADGO是否等于0，重復(fù)開啟AD轉(zhuǎn)換。

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9、讀取結(jié)果

AD轉(zhuǎn)換結(jié)果保存在ADRES0L和ADRES0H寄存器，對齊方式在上面已提到。

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觸摸檢測程序設(shè)計(jì)

實(shí)現(xiàn)效果：

??按下按鍵，4位數(shù)碼管<2:0>顯示“YES”，未按下時(shí)顯示“NO”；數(shù)碼管<3>顯示按下次數(shù)，最多記到16次；按下按鍵時(shí)LED燈閃亮。

引腳使用：

??PORTA<3:0>為數(shù)碼管片選位，PORTC<7:0>為數(shù)碼管段選位；PORTB<7>為LED燈位。

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設(shè)計(jì)思路：

??ADC模塊循環(huán)預(yù)充電、采樣、AD轉(zhuǎn)換，獲取電壓變化并與閾值比較判斷是否觸摸；定時(shí)器5ms中斷一次，判斷ADC是否轉(zhuǎn)換完成，計(jì)數(shù)并把ADRES中的轉(zhuǎn)換結(jié)果同步到數(shù)碼管的顯示緩沖區(qū)，隨后再次預(yù)充電、采樣并開啟AD轉(zhuǎn)換。

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基于PIC16F18854單片機(jī)的cC語言源代碼：

#include <xc.h> #ifndef BOOTLOADER//配置段// PIC16F18854 Configuration Bit Settings// 'C' source line config statements// CONFIG1 #pragma config FEXTOSC = OFF // External Oscillator mode selection bits (Oscillator not enabled) #pragma config RSTOSC = HFINT1 // Power-up default value for COSC bits (HFINTOSC (1MHz)) #pragma config CLKOUTEN = OFF // Clock Out Enable bit (CLKOUT function is disabled; i/o or oscillator function on OSC2) #pragma config CSWEN = ON // Clock Switch Enable bit (Writing to NOSC and NDIV is allowed) #pragma config FCMEN = OFF // Fail-Safe Clock Monitor Enable bit (FSCM timer disabled)// CONFIG2 #pragma config MCLRE = ON // Master Clear Enable bit (MCLR pin is Master Clear function) #pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled) #pragma config LPBOREN = OFF // Low-Power BOR enable bit (ULPBOR disabled) #pragma config BOREN = ON // Brown-out reset enable bits (Brown-out Reset Enabled, SBOREN bit is ignored) #pragma config BORV = LO // Brown-out Reset Voltage Selection (Brown-out Reset Voltage (VBOR) set to 1.9V on LF, and 2.45V on F Devices) #pragma config ZCD = OFF // Zero-cross detect disable (Zero-cross detect circuit is disabled at POR.) #pragma config PPS1WAY = OFF // Peripheral Pin Select one-way control (The PPSLOCK bit can be set and cleared repeatedly by software) #pragma config STVREN = ON // Stack Overflow/Underflow Reset Enable bit (Stack Overflow or Underflow will cause a reset)// CONFIG3 #pragma config WDTCPS = WDTCPS_31 // WDT Period Select bits (Divider ratio 1:65536; software control of WDTPS) #pragma config WDTE = SWDTEN // WDT operating mode (WDT enabled/disabled by SWDTEN bit in WDTCON0) #pragma config WDTCWS = WDTCWS_7 // WDT Window Select bits (window always open (100%); software control; keyed access not required) #pragma config WDTCCS = SC // WDT input clock selector (Software Control)// CONFIG4 #pragma config WRT = WRT_upper // UserNVM self-write protection bits (0x0000 to 0x01FF write protected) #pragma config SCANE = not_available // Scanner Enable bit (Scanner module is not available for use) #pragma config LVP = ON // Low Voltage Programming Enable bit (Low Voltage programming enabled. MCLR/Vpp pin function is MCLR.)// CONFIG5 #pragma config CP = OFF // UserNVM Program memory code protection bit (Program Memory code protection enabled) #pragma config CPD = OFF // DataNVM code protection bit (Data EEPROM code protection disabled)// #pragma config statements should precede project file includes. // Use project enums instead of #define for ON and OFF. #endifunsigned char seq_table[16] = {0b00111111, //00b00000110, //10b01011011, //20b01001111, //30b01100110, //40b01101101, //50b01111101, //60b00000111, //70b01111111, //80b01101111, //90b01110111, //a0b01111100, //b0b00111001, //c0b01011110, //d0b01111001, //e0b01110001 //f }; //段碼表unsigned char code_table[4] = {0b11110111,0b11111011,0b11111101,0b11111110}; //位碼表unsigned char display_table[4]; //顯示緩沖區(qū) int touch_count; //按動(dòng)次數(shù)計(jì)時(shí)器 int touch_flag; //按動(dòng)記錄標(biāo)志位 int mode = 0; //mode == 0 means print "yes" or "no"; mode == 1 means print voltage ADC numbervoid __interrupt() ISR(void); void seq_code_sel(int i); void Init(); void Init_timer(); void Init_ADC();void main(void) {unsigned char i = 0;touch_count = 0;touch_flag = 0;Init();while (1){seq_code_sel(i);i = (i + 1) % 4;} }void __interrupt() ISR(void) {PIR0bits.TMR0IF = 0; //clear the signal bitTMR0H = 0x3c;TMR0L = 0xb0;if (mode){if (ADRES){display_table[0] = touch_count;display_table[1] = (ADRES / 100) % 10;display_table[2] = (ADRES / 10) % 10;display_table[3] = ADRES % 10;}}else{if (ADRES > 800) //設(shè)置閾值為 800{PORTB = 0;display_table[0] = seq_table[touch_count];display_table[1] = 0;display_table[2] = 0x37;display_table[3] = 0x3f;touch_flag = 1;}if (ADRES < 800){PORTB = 0x80;if (touch_flag){touch_count = (touch_count + 1) % 16;touch_flag = 0;}display_table[0] = seq_table[touch_count];display_table[1] = 0x6e;display_table[2] = 0x7b;display_table[3] = 0x6d;}}if (ADCON0bits.ADGO == 0){ADPRE = 0b00010000; //Precharge time is 128 clocks of the selected ADC clockADACQ = 0b00010000; //Acquisition time is 128 clocks of the selected ADC clockfor (int wait = 0; wait < 16; wait++); //wait for acquisition timeADCON0bits.ADGO = 1;} }void Init() {//Init PORTA,PORTB,PORTCPORTA = 0;LATA = 0;ANSELA = 0x80;TRISA = 0x80; //Set RA7 to inputPORTB = 0;LATB = 0;ANSELB = 0;TRISB = 0;PORTC = 0;LATC = 0;ANSELC = 0;TRISC = 0;Init_timer();Init_ADC(); }void Init_ADC() {//Init ADCADCLKbits.ADCCS = 0b000001; //FOSC/4ADCON1bits.ADPPOL = 0; //IO pin shorted to VSS, Chold shorted to AVDDADCON0bits.ADCS = 0; //Clock supplied by FOSC, divided according to ADCLK registerADCON0bits.ADFRM0 = 1; //ADRES and ADPREV data are right-justifiedADREFbits.ADPREF = 0b11; //VREF+ is connected to FVRADREFbits.ADNREF = 0b0; // VREF- is connected to VSSFVRCONbits.FVREN = 1; //FVR enableFVRCONbits.ADFVR = 0b11; //ADC FVR Buffer Gain is 4x, (4.096V)FVRCONbits.FVRRDY = 1; //Fixed Voltage Reference output is ready for useADCON1 = 0b00000000; // default ADPPOL, no ADDSENADCON2 = 0b00000000; // legacy modeADCON3 = 0b00000000; // default, no interruptADPCH = 0b000111; //ADC Positive Input Channel Selection == RA7ADCAP = 0b101; //ADC Additional Sample Capacitor == 5pFADPRE = 0b00010000; //Precharge time is 128 clocks of the selected ADC clockADACQ = 0b00010000; //Acquisition time is 128 clocks of the selected ADC clockfor (int wait = 0; wait < 16; wait++);//wait for acquisition timeADCON0bits.ADON = 1; //Turn ADC On }void Init_timer() {//Timer interruptINTCONbits.GIE = 1;PIR0bits.TMR0IF = 0; //clear the signal bitPIE0bits.TMR0IE = 1; //interrupt enable//Timer0 configurationT0CON0 = 0b00010000;T0CON1 = 0b01000000;TMR0H = 0x3c;TMR0L = 0xb0;T0CON0bits.T0EN = 1; }void seq_code_sel(int i) {PORTA = code_table[i];if (mode){PORTC = seq_table[display_table[i]];}else{PORTC = display_table[i];}for (int temp = 0; temp < 100; temp++); }

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