Using the HT45R36 and HT45R38 to implement Touch Switches

Transcription

1 Using the HT45R36 and HT45R38 to implement Touch Switches D/N: HA0115E Introduction This example uses the C/R to F internal feature of the HT45R36 and HT45R38 to implement a Touch Switch. It is one way of using sensed human body capacitance effects to implement a switch function. The switch requires no pressure, only an insulating layer on the switch which if lightly touched will be sensed. These types of switches offer the advantages of no wear-out, easy cleaning and safe operation etc. Device Characteristics At the centre of the Touch Switch is a C/R-F or Capacitance/Resistance to Frequency Converter function. Both the HT45R36 and HT45R38 have this internal function. The following table shows the main resources available within each device. Timer Interrupt LED C/R-F Part No. ROM RAM I/O Driver Channel 8-bit 16-bit Ext. Int. Output A/D PWM OPA Stack Package HT45R36 2Kx14 120x x QFP, 52QFP HT45R38 4kx15 192x x8 12-bitx5 8-bitx QFP The HT45R38 in addition to having a C/R-F function, also includes A/D, PWM and OPA internal functions and is an A/D+C/R-F function type MCU. The HT45R36 is an I/O+C/R-F function MCU. 1

2 Operating Principle The Touch Switch uses the effects of human body capacitance to alter the value of the C/R-F circuit capacitance value, which in turn changes the frequency of its oscillator. By measuring difference in the frequency it is possible to detect if the switch has been touched. The C/R-F circuit is shown in Figure 1. The IN (0Ω), RREF (27kΩ) and CREF (10pF) pins are connected to fixed value resistors and capacitors. The values in brackets show the laboratory used resistor and capacitor values which can be used for reference. The RC OSC circuit will generate a frequency value as a reference value. When the resistance or the capacitance value connected to the RC pin changes, then the RC OSC circuit oscillator frequency will also change. When a human hand or finger touches the Touch Switch, it is similar to adding a capacitor, which will reduce the oscillator frequency. The application program only has to detect certain changes to the reference frequency to ascertain whether the switch has been touched or not. The ASON register is used to select the channel: 00000b=TG1 on, others off 00001b=TG2 on, others off 01111b=TG16 on, others off b=all TGs off, save mode 2

3 The program uses ASON to activate TG1~TG16, which in turn will scan the corresponding individual RC1~RC16 touch switches. Figure 1:C/R-F circuit block diagram RC1 RC2 RC3 RC RC16 Figure 2:Touch Switch 3

4 The MCU uses a comparison method to obtain the RC OSC value. The operating principle is shown in Figure 3. For example if Timer A is setup to generate an overflow every 1ms, then read the Timer B count value, and then divide the Timer B value by Timer A, to get the frequency. Actually the program does not have to calculate the frequency value. Instead, within the fixed time setup by Timer A, it only has to determine if there are changes to the reference frequency Timer B count (touch switch off) and the present Timer B count. If the change has exceeded an already setup value of sensitivity, then it can be determined if the touch switch has been activated or not. S1 System Clock System Clock/4 S2 Timer A OVB=0 Interrupt T1ON OVB=1 Timer B Reset T1ON RC OSC Output Start Overflow Timer A Timer B 1ms 1 2 Figure 3 3 Timer B Count=1000 RC OSC f=1mhz 4

5 Application Circuit Diagram +VBB VSS VSS V1 V2 V3 V4 +VBB VSS VSS P1 +VBB 470uF/25V + C P2 C uF/16V 3 + C3 C5 104 VSS R1 470uF/16V R B C6 C4 104 VSSC C7 R3 R4 10PF 27K VSSC CREF 23 RREF 24 IN 25 KOUT B RES OSC1 OSC2 VSS S1 C K1 RESET C8 Y1 R6 4M C9 R5 ROSC2 R8 100K R9 10K C12 0.1uF OSC1 C13 0.1uF S2 R7 ROSC1 C10 470P RC1 RC2 RC3 RC4 RC5 RC6 RC7 RC8 RC9 RC10 RC11 RC12 RC13 RC14 RC15 RC PC0 PB7 PB6 PB5 PB4 B PB3 PB2 PB1 PB0 PA7 PA6 PA5 PC1 PC2 PC3 VSSC PC4 PC5 PC6 PC7 PD0 CREF RREF IN KOUT HT45R36 PA4 PA3/TMR1 PA2/TMR0 PA1/INT1 PA0/INT0 RES OSC1 OSC2 VSS RC16 RC15 RC14 RC1 RC2 RC3 RC4 RC5 RC6 RC7 RC8 RC9 RC10 RC11 RC12 RC U U2 K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 K11 K12 K13 K14 K15 K16 Figure 4 K1~K16 in Figure 4 connect to the touch switches shown in Figure 2. Note that because the effect of environmental temperature on the resistor and capacitor is quite big, the RC OSC oscillation frequency of the touch switch has no fixed frequency when activated. Therefore during periods when the switch is not touched, the reference frequency Timer B Count value should be recalculated, to maintain its real-time properties and to prevent erroneous Touch Switch operation. 5

6 Example Program ;;=============================================================== ;;**********File Name: Main.Asm************** ;;HT_IDE Version: V6.6 SP5 ;;Main Function: **Touch Switch ** ;;MCU Body: HT45R36 ;;: 5V ;;MCU Frequency: 4MHz ;; ;;Mask Option: ;; ;Osc: Crystal ;Fsys: 4MHz ;Wdt: Disable ;WDT Clock Source: T1 ;CLR WDT: One clear instruction ;Wake_Up PA.0-7: Non-Wake-Up ;Pull-high PA: PULL-HIGH ;Pull-high PB: PULL-HIGH ;Pull-high PC: PULL-HIGH ;Pull-high PD: PULL-HIGH ;INT0 trigger edge Disable ;INT1 trigger edge Disable ;LVR: Disable ;;================================================ #INCLUDE HT45R36.INC ;;================================================ MMOV MACRO TEMP1,TEMP2 MOV A, TEMP2 MOV TEMP1, A ENDM ;;==================================== PUSH MACRO ;; Interrupt routine entry MOV ACC_STACK, A MOV A, STATUS MOV STATUS_STACK, A MOV A, MP0 MOV MP0_STATE, A ENDM ;;==================================== POP MACRO ;; return from interrupt MOV A, MP0_STATE MOV MP0, A MOV A, STATUS_STACK MOV STATUS, A MOV A, ACC_STACK RETI ENDM 6

7 ;;==================================== LXXXX EQU 4167 ;;TIMERA initial value, corresponding time ;; is equal to 4.167ms D_CHECK EQU ;;TIMERA initial value, corresponding time ;; is equal to ms INITIAL_COUNT EQU 50 ;;setup no switch touch cycle number, if 50 ;; cycles with no switch touch, then obtain ;; new reference frequency TIMERB COUNT, to ;;obtain new interval time X_X EQU 50 ;;setup Sensitivity value ;;==================================== DATA_MAIN.SECTION 'DATA' ACC_STACK DB? STATUS_STACK DB? MP0_STATE DB? MP1_STATE DB? MODE_CX DB? RF_CX DB? RF_DX DB? SAVE_RF_DX DB? RF_EX DB? BUF0 DB? BUF1 DB? BUF2 DB? BUF3 DB? BUF00 DB? BUF10 DB? DEL0 DB? DEL1 DB? DEL2 DB? ZERO DB? KEY_NUMBER DB? ;; Store activated Touch Switch code INITIAL_RCOSC_FLAG DBIT ;; 16 Touch Switch off - TIMERB COUNT value ;; scan ended flag SCAN_RCOSC_FLAG DBIT ;; 16 Touch Switch scan ended flag TIMER1_ISR_FLAG DBIT ;; Enter TIMER1 interrupt routine flag F_KEY_ON DBIT ;; Touch Switch activated flag ORG 029H RF_DATA DB 32 DUP (?) ;; Store 16 Touch Switch off TIMERB ;; COUNT value (16bit) ;;================================================ CODE_MAIN.SECTION AT 00H 'CODE' JMP MAIN_START ORG 004H RETI ORG 008H 7 ;;not used ;;not used

8 RETI ORG 00CH ;;no used RETI ORG 010H ;;TIMER1 interrupt JMP TIMER1_ISR ;;======================================================================= ======== MAIN_START: CALL INITIAL_SUB CALL SCAN_KEY_INITIAL_SUB CALL DELAY_300MS CLR SCAN_RCOSC_FLAG CALL FIRST_TIME_SETUP 8 ;; program initialisation ;; reference frequency(touch Switch off) ;; TIMERB COUNT value store in ;; BANK0 [50H~6FH] ;; Delay 300ms ;; immediate scan TIMERB COUNT store in ;; BANK 1 [40H~5FH] SCAN_ALL_KEY: MOV A, 00H MOV RF_DX, A CLR F_KEY_ON CHECK_SUB: CLR INTC1.0 CALL FIRST_CHECK_SUB ;; Compare with BANK0 [50H~6FH]and ;; BANK1 [40H~5FH] value SNZ C ;; BANK0 [50H~6FH]> BANK1 [40H~5FH]? JMP SCAN_NEXT ;; NO MOV A, BUF2 ;; YES SUB A, X_X ;; Compare difference value and setup ;; Sensitivity value MOV A, BUF3 SBC A, ZERO SNZ C ;; Is Touch Switch activated? JMP SCAN_NEXT ;; NO SET F_KEY_ON ;; YES - setup Touch Switch activated flag MOV A, RF_DX MOV SAVE_RF_DX, A ;; Store activated Touch Switch ;; corresponding channel (ASON) SCAN_NEXT: ;; Continue scan next Touch Switch SET INTC1.0 SNZ TIMER1_ISR_FLAG JMP $-1 CLR TIMER1_ISR_FLAG INC RF_DX MOV A, RF_DX

9 XOR A, 010H SNZ Z ;; Is 16 Touch Switch scan finished? JMP CHECK_SUB ;; NO, scan next Touch Switch SNZ F_KEY_ON ;; YES, any switch pressed? JMP NO_KEY ;; NO MOV A, SAVE_RF_DX ;;YES INC ACC MOV KEY_NUMBER, A ;; Store Touch Switch code into ;; KEY_NUMBER MMOV RF_EX, INITIAL_COUNT JMP SCAN_ALL_KEY NO_KEY: ;;No 16 Touch Switches activated SET KEY_NUMBER SDZ RF_EX JMP SCAN_ALL_KEY CALL L_SAVE_INITIAL ;;After 50 cycle scan if no 16 ;; Touch Switches pressed then renew ;; reference frequency TIMERB COUNT value MMOV RF_EX, INITIAL_COUNT JMP SCAN_ALL_KEY ;;======================================================================= = INITIAL_SUB: ;;Initialisation CLR_BANK0: ;;BANK0 cleared to zero MOV A, 28H MOV MP0, A MOV A, 88 CLR_BANK0_LP: CLR R0 INC MP0 SDZ ACC JMP CLR_BANK0_LP CLR_BANK1: ;;BANK1 cleared to zero MMOV BP, 01H MOV A, 40H MOV MP1, A MOV A, 32 CLR_BANK1_LP: CLR R1 INC MP1 SDZ ACC JMP CLR_BANK1_LP SET KEY_NUMBER MMOV RF_EX, INITIAL_COUNT CLR PB ;;setup I/O CLR PBC CLR PC CLR PCC CLR INTC0 9

10 CLR INTC1 CLR TMR0C CLR TMR1C MOV A, 01H MOV INTC0, A MOV A, 01H MOV INTC1, A MOV A, 020H MOV TMR1C, A MOV A, 02H ;;enable global interrupt ;;enable TIMER1 interrupt ;;TIMER1:TIMER MODE(SYSTEM CLOCK/4) MOV RCOCR, A ;;RC OSCILLATION CONVERTER MODE CLR TMRBL CLR TMRBH MOV A, RF_CX MOV ASCR, A RET ;;======================================================================= = SCAN_KEY_INITIAL_SUB: ;; reference frequency(touch Switch off) ;;TIMERB COUNT store to BANK0 [50H~6FH] CLR MODE_CX CLR RF_CX CLR ASCR ;;Select channel 1 scan Touch Switch 1 CLR TMRBL CLR TMRBH MMOV TMRAL, LOW (65536-D_CHECK) ;;TIMERA time setup as ms MMOV TMRAH, HIGH (65536-D_CHECK) SET TMR1C.4 ;;Start TIMER1 CLR INITIAL_RCOSC_FLAG SNZ INITIAL_RCOSC_FLAG JMP $-1 ;;Wait for end of 16 Touch Switch scan RET ;;======================================= FIRST_TIME_SETUP: ;;Immediate scan TIMERB COUNT store to ;; BANK1 [40H~5FH] MMOV MODE_CX, 01H MOV A, 00H MOV RF_CX, A MOV ASCR, A ;;Select Channel 1 scan Touch Switch 1 CLR TMR1C.4 CLR TMRBL CLR TMRBH MMOV TMRAL, LOW (65536-LXXXX) ;;Setup TIMERA time to 4.167ms MMOV TMRAH, HIGH (65536-LXXXX) SET TMR1C.4 ;;Start TIMER1 SNZ SCAN_RCOSC_FLAG JMP $-1 RET ;;======================================= ;;Wait for end of 16 Touch Switch scan 10

11 FIRST_CHECK_SUB: MOV A, 40H ADD A, RF_DX ADD A, RF_DX MOV MP1, A MOV A, R1 MOV BUF0, A INC MP1 MOV A, R1 MOV BUF1, A MOV A, 50H ADD A, RF_DX ADD A, RF_DX MOV MP0, A MOV A, R0 SUB A, BUF0 MOV BUF2, A INC MP0 MOV A, R0 SBC A, BUF1 ;; BANK0 [50H~6FH] - BANK1 [40H~5FH] ;;corresponding TIMERB COUNT ;; low byte subtraction ;;corresponding TIMERB COUNT ;; high byte subtraction MOV BUF3, A RET ;;===================================================================== L_SAVE_INITIAL: MMOV MP0_STATE, INTC0 CLR INTC0.0 MMOV MP0, 050H MMOV MP1, 040H MMOV DEL0, 32 L_SAVE_INITIAL_LOOP: MMOV R0, R1 INC MP0 INC MP1 SDZ DEL0 JMP L_SAVE_INITIAL_LOOP ;;Renew reference frequency ;;(Touch Switch off) TIMERB COUNT value MMOV INTC0, MP0_STATE RET ;;======================================================================= TIMER1_ISR: ;; TIMER1 interrupt routine PUSH SET TIMER1_ISR_FLAG MOV A, MODE_CX ADDM A, PCL JMP MODE_CX_0 ;; SET INITIAL_RCOSC_FLAG & TIMERB COUNT ;; value into BANK0 [50H~6FH] JMP MODE_CX_1 ;; SET SCAN_RCOSC_FLAG & (TIMERB COUNT 11

12 ;; multiplied by 4 into [40H~5FH] OF BANK1 POP ;; MODE_CX_0: MOV A, TMRBH MOV BUF1, A MOV A, TMRBL MOV BUF0, A MOV A, 50H ADD A, RF_CX ADD A, RF_CX MOV MP0, A ;; Place the TIMERB COUNT value into BANK0 ;; [50H~6FH] MOV A, BUF0 MOV R0, A INC MP0 MOV A, BUF1 MOV R0, A INC RF_CX MOV A, RF_CX MOV ASCR, A ;; Open the 1~16 channels, start scanning ;; the 16 switches XOR A, 010H SNZ Z JMP SCAN_LP_0 SET INITIAL_RCOSC_FLAG ;; YES,setup the related flag JMP EXIT_TIMER1_ISR_0 SCAN_LP_0: CLR TMRBL CLR TMRBH MMOV TMRAL, LOW (65536-D_CHECK) MMOV TMRAH, HIGH (65536-D_CHECK) SET TMR1C.4 JMP EXIT_TIMER1_ISR_0 EXIT_TIMER1_ISR_0: POP ;; MODE_CX_1: MOV A, MP1 MOV MP1_STATE, A MOV A, TMRBH MOV BUF10, A MOV A, TMRBL MOV BUF00, A CLR C RLC BUF00 ;; Multiply TIMERB COUNT by 2 RLC BUF10 CLR C RLC BUF00 ;; Multiply TIMERB COUNT by 2 ;; Is scanning complete of the 16 switches? ;; NO 12

13 RLC BUF10 MOV A, 40H ADD A, RF_CX ADD A, RF_CX MOV MP1, A ;; by 4 into BANK1 [40H~5FH] MOV A, BUF00 MOV R1, A INC MP1 MOV A, BUF10 MOV R1, A INC RF_CX MOV A, RF_CX MOV ASCR, A ;; Place the TIMERB COUNT value multiplied ;; open 1~16 channels, scan corresponding ;; 16 Touch Switches XOR A, 010H SNZ Z ;; 16 Touch Switch scanning ended? JMP SCAN_LP_1 ;; NO SET SCAN_RCOSC_FLAG ;; YES, setup related flag CLR RF_CX MOV A, RF_CX MOV ASCR, A SCAN_LP_1: CLR TMRBL CLR TMRBH MMOV TMRAL, LOW (65536-LXXXX) MMOV TMRAH, HIGH (65536-LXXXX) SET TMR1C.4 JMP EXIT_TIMER1_ISR_1 EXIT_TIMER1_ISR_1: ;; exit TIMER1 interrupt routine MOV A, MP1_STATE MOV MP1, A POP ;;======================================= DELAY_300MS: ;; Delay 300ms CLR DEL1 CLR DEL0 SDZ DEL0 JMP $-1 SDZ DEL1 JMP $-3 RET ;;======================================================================= 13

14 Software Description: RC1~RC16 have corresponding 1~16 touch switches. KEY_NUMBER stores the scanning result. If no switches have been touched then KEY_NUMBER will have the value FFH. If switches have been touched, then KEY_NUMBER will contain the switch code. Additionally, after power has been applied to the system, the switches should not be touched for 0.3ms, as during this time the system will scan the switches to obtain the reference frequency touch switch off Timer B count value. 14