Capacitive Touch Button by using ADC channel (the CVD system)

[ero]

I would like to use one touch button (or pad) with pic and I read the pdf file of Microchip AN1298 about that matter.
The document gives the following instructions to do the job;
* 1. Set 2nd channel to output, set high (VDD)
* 2. Select 2nd channel on ADC (charges CHOLD to VDD).
* 3. Set sensor line to output, set low (GND)
* 4. Select sensor line as input (TRISx = 1)
* 5. Select sensor channel on ADC (V-div sensor:CHOLD)
* 6. Begin ADC conversion
* 7. Reading is in ADRESH:ADRESL
I decided to write a program for 12F676 considering these explanations.
Here is the program . Could you pls someone check the program and let me know if there are some mistakes or missed points. Because the program does not work as I want.

@ DEVICE pic12F675                                                     
@ DEVICE pic12F675, WDT_ON             
@ DEVICE pic12F675, PWRT_ON             
@ DEVICE pic12F675, PROTECT_OFF         
@ DEVICE pic12F675, MCLR_off            
@ DEVICE pic12F675, INTRC_OSC_NOCLKOUT  

DEFINE OSCCAL_1K 1  

DEFINE OSC 4

DEFINE ADC_BITS 8    
'DEFINE ADC_CLOCK 1    
DEFINE ADC_SAMPLEUS 10 
CMCON = 7
RAW VAR byte 56
OPTION_REG=%01001111
GPIO=0
TRISIO=0
ANSEL = %01011111
ADCON0=%00001001
WPU=0
START:     
       ANSEL.2=1         'GPIO.2 Analog selected  This is secondary channel 
       GPIO.2=1          'GPIO.2=HIGH this is for charging the C_hold capacitor 
       OUTPUT GPIO.2     'GPIP.2 is output now
       ADCON0=%00001001  'AN2 (GPIO.2) selected for ADC purpose
       PAUSEus 10   
       
       TRISIO.4=0        'AN3=is output , this is sensor pin
       GPIO.4=0          'AN3 is LOW yapıldı This for discharging the sensor capacitor 
       TRISIO.4=1        'AN3= is input now 
       ANSEL.3=1         'AN3 is analog input now
       ADCON0=%00001101  'ADC =AN3 redierected to AN3 and  C_hold voltage is divided (CVD )
       pauseus 10        'wait 10 us 
       ADCIN 3,RAW
       ANSEL.2=0         'GPIO.2 is Digital for re-use it on next cycle 
      
       OUTPUT GPIO.4          'Sensor pin is Output now 
       
       GPIO.5=1               'GPIO.5=HIGH , sensor pin is HIGH 
       PAUSE RAW              'wait as HAM value (ms)
       GPIO.5=0               'GPIO.5=LOW Output is LOW now. 
       pause 10
       GOTO START

[readitaloud]

Ero

GPIO.2 must remain an input all the time. Tie this input to Vcc. Tell the ADC to select GPIO.2 input pin as an analog input to charge the C_hold cap.

- Martin

[ero]

Thank you for the reply. I will do them.

Ero

[Max Power]

ero, Martin, or anybody

I've been trying to do this with a PIC16F819, with only mediocre results. My 819 has a 10 bit A2D, while I see that you are trying it with a 8 bit A2D, so theoretically, your results should be even worse than mine, if that's possible. so, I'm interested in what your typical RAW value is, what it drops to with a finger press, and if it stays relatively constant while your finger is near, because mine does not.

I started out not tying any of the A2D inputs directly to VCC, and my program began with the A2D pins TRIS being outputs. It worked, sort of, but the A2D value was not constant while my finger was near the pad. Then, I read Martin's suggestion, tied my 'dummy' A2D channel to VCC, modified the code, and ... same thing.

I've got my PIC16F819 on a olimex 18 pin dev board. I have two copper tape pads, about 1 inch square, covered with electrical tape, on pins 2 and 18.

my debug statement spits out usually 30 for my untouched S2_AVE (which is not really an average) and when i put my finger on the sensor, it jumps (rings) between 1 and 37. :-(

I tried putting 10uS delays all over my sense subroutine, tried a longer or no pause before running the A2D, and I tried messing with the A2D clock source, which now doesn't match the define statement.

oh yeah, I tried to manually control the A2D, but that didn't work. I think I'm pointing to the wrong bits

If anybody is still with me, here is my down-n-dirty, non-averaging, non-optimized, soon to be pitched, code.
I'd love to hear any suggestions.

							'    PIC BASIC PRO 2.6 & MPLAB v8.40 PIC16F819 
'    ================


@ __CONFIG  _HS_OSC & _MCLR_OFF  &  _LVP_OFF & _WDT_OFF & _PWRTE_OFF  & _BODEN_OFF

DEFINE DEBUG_REG PORTB        ' asyncronous RS-232 output on PORTB...
DEFINE DEBUG_BIT 7        ' bit 7
DEFINE DEBUG_BAUD 19200        ' 19200 Baud, 
DEFINE DEBUG_MODE 0        ' 1 = inverted,  0 = true,like for using max232, or pickit2
DEFINE DEBUG_PACING 1000    ' 1mS delay 

DEFINE  ADC_BITS        10    ' Set number of bits in result
DEFINE  ADC_CLOCK       3    ' Set clock source (3=rc)
DEFINE  ADC_SAMPLEUS    50    ' Set sampling time in uS

DEFINE OSC 20    

PORTA = 0
PORTB = 0

TRISA = %00000100        ' dummy channel = PortA.2 = tied to VCC
TRISB = %00000100           ' pushbutton input   


PUSHB          var PORTB.2        ' Pushbutton    (OLIMEX 18 pin PIC dev board - active low)
REDLED        var PORTB.3        ' Indicator LED (OLIMEX 18 pin PIC dev board)
YELLOWLED     var PORTB.5    
GREENLED     var PORTB.6


S1_AVE        var word 
S2_AVE        var word 
S1value        var word 
S2value        var word 
counter        var word 

ADGO    VAR ADCON0.0
ADDONE    VAR ADCON0.2

DEBUG REP $00\8,13,10,"Starting Up"


ADCON0 = %10010000            '10 = A2D freq FOSC/64
                    '010 = point to the dummy channel, AN2
                    '0 = status bit
                    '0 = unused
                    '0 = "ADON", 1 = on
                

ADCON1 = %11000000              '1 = right justified
                    '1 = A/D clock divide by 2 is used
                    '00 = unused
                    '0000 = all analog inputs


PAUSE 1000


counter = 0

GOSUB SENSE1
GOSUB SENSE1
GOSUB SENSE1
S1_AVE = S1value

GOSUB SENSE2
GOSUB SENSE2
GOSUB SENSE2
S2_AVE = S2value



mainloop:

GOSUB SENSE1

IF S1value < (S1_AVE-3) THEN
    GREENLED =1 
ELSE 
    GREENLED =0
ENDIF


GOSUB SENSE2

IF S2value < (S2_AVE-3) THEN
    YELLOWLED =1 
ELSE 
    YELLOWLED =0
ENDIF


IF PUSHB = 0 THEN
    DEBUG DEC S1_AVE, ", ",DEC S1value,", ", DEC S2_AVE, ", ",DEC S2value,13,10
ENDIF


counter = counter +1

IF counter > 3000 THEN
    TOGGLE REDLED
    counter = 0
ENDIF


GOTO mainloop


' *   Microchip AN1298: CVD Touch Sensing using two ADC channels
' *
' *  1. Set 2nd channel to output, set high (VDD)
' *  2. Select 2nd channel on ADC (charges CHOLD to VDD).
' *  3. Set sensor line to output, set low (GND)
' *  4. Select sensor line as input (TRISx = 1)
' *  5. Select sensor channel on ADC (V-div sensor:CHOLD)
' *  6. Begin ADC conversion
' *  7. Reading is in ADRESH:ADRESL



SENSE1:
'setup and read the first sensor (PORTA1, AN1, pin 18)

'TRISA.2 = 0           'Set Dummy channel to digital output
'PORTA.2 = 1         ' Dummy channel goes high
ADCON0 = %10010000    ' set A/D to dummy channel  
PAUSEUS 10        ' let it charge
PORTA.1 = 0         'Sensor line gets set low
TRISA.1 = 0        'Sensor line gets set to digital output
TRISA.1 = 1        'Sensor line gets set to digital/analog input
ADCON0 = %10001000     'Point A/D to sensor line
PAUSEUS 10        'wait for voltage to stabilize
ADCIN 1, S1value    ' Read channel 1 to variable 

'ADGO = 1        'turn on A/D
'WHILE ADDONE = 1
'WEND
'S1value = ADRESL

TRISA.1 = 0           'return sense line to be digital output
RETURN


SENSE2:
'setup and read the 2nd sensor (PORTA3, AN3, pin 2)

'TRISA.2 = 0           'Set Dummy channel to digital output
'PORTA.2 = 1         ' Dummy channel goes high
ADCON0 = %10010000    ' set A/D to dummy channel  
PAUSEUS 10        ' let it charge
PORTA.3 = 0         'Sensor line gets set low
TRISA.3 = 0        'Sensor line gets set to digital output
TRISA.3 = 1        'Sensor line gets set to digital/analog input
ADCON0 = %10011000     'Point A/D to sensor line
PAUSEUS 10        'wait for voltage to stabilize
ADCIN 3, S2value    ' Read channel 3 to variable 

'ADGO = 1        'turn on A/D
'WHILE ADDONE = 1
'WEND
'S2value = ADRESL

TRISA.3 = 0           'return sense line to be digital output
RETURN


END

[ero]

Max Power,

I need to make a correction. 12F675 having 10 bit ADC channels but I was using them as 8 bit. Because in that job I do not need 10 bit conversation.

I made a system which is working without any problem. But it was not so easy to do that. Because as I told on my first message the system does not work with stability. Let say if you touch the touch point it is not coming the same result all the time. There is like a loop and after that loop you obtain again the same result.
For instance the ADC value is depend on what you use as touch point (cable , cupper plate etc) The capacity of that equipments are changing the ADC value.
I was using one short (about 25 cm) thick cable (single line inside). With that cable I was getting $85 value without touching to the cable. If I touch the ADC value was going down as zero ("0") This was the trick for me to catch the touch moment. BUt as I told you it was not stabil. Finally I decided to use also one loop to eliminate the false signals. Finally my siystem is working very well without any problem. I made both TOGGLE system and also NON-TOGGLE system.
Here is the codes for Toggle system;

* : TOGGLE *
'************************************************* ***************
@ DEVICE pic12F675
@ DEVICE pic12F675, WDT_ON
@ DEVICE pic12F675, PWRT_ON
@ DEVICE pic12F675, PROTECT_OFF
@ DEVICE pic12F675, MCLR_off
@ DEVICE pic12F675, INTRC_OSC_NOCLKOUT

DEFINE OSCCAL_1K 1

DEFINE OSC 4

DEFINE ADC_BITS 8
'DEFINE ADC_CLOCK 1
DEFINE ADC_SAMPLEUS 10
CMCON = 7
RAW VAR byte 56
TOP VAR WORD
SINIR VAR BYTE
I VAR BYTE
BUYUK var byte
KUCUK VAR BYTE
poz var bit
OPTION_REG=%01001111
GPIO=0
TRISIO=0
ANSEL = %01011111
ADCON0=%00001001
WPU=0
GPIO.2=1
SINIR=132 'This is the sensibility value can reach up to 136 according to my touching cable and it can be changed for the different material.
BUYUK=0
KUCUK=255

START:
GOSUB TUSBAK
'------------------------do not use these lines I was used them to see the ADC values-------------------------------
IF RAW>BUYUK THEN BUYUK=RAW
IF RAW>0 and RAW<KUCUK THEN KUCUK=RAW
WRITE $10,BUYUK
WRITE $11,KUCUK
'-------------------------------------------------------------------------------------------------------------------
IF RAW<SINIR and POZ=0 THEN 'this is the lines to eliminate the false loop
TOGGLE GPIO.5
I=0oz=1
BIR: gosub tusbak
IF RAW<SINIR then
I=0
GOTO BIR
ELSE
I=I+1
IF I<SINIR then BIR
ENDIF
pause 50
I=0
goto start
endif

pause 10
poz=0
GOTO START
TUSBAK: 'means check if there is a touch
GPIO.2=0
ANSEL.2=0
HIGH GPIO.2
ADCON0=%00001001 ' The direction of ADC channel is now GPIO.2 and C_hold is charging by the signal coming from AN2.
ANSEL.0=0 'sensor pin is digital
TRISIO.0=0 'sensor pin is now output pin
GPIO.0=0 'sensor pin is LOW and it was discharged
TRISIO.0=1 'Sensor pin is again input
ANSEL.0=1 'sensor pin is analog input now
ADCIN 0,RAW
BAK:
TRISIO.0=0
ANSEL.0=0
GPIO.0=0
RETURN

I hope everything is clear now.

Ero

[Charlie]

I've made a touch controlled dimmer with touch up/touch down controls using this method. There is a lot of variability in the measurement, but empirically I determined a range of values that the result always falls within when touched. I then implemented a "tell me three times" loop to eliminate noise. I'm happy with the result and there are several complete units in use with no complaints.

I can't post the code because I sold the rights to it, but the only tricks to making it work are in the paragraph before this one.

[Normnet]

I would like to use one touch button (or pad) with pic and I read the pdf file of Microchip AN1298 about that matter.
The document gives the following instructions to do the job;
* 1. Set 2nd channel to output, set high (VDD)
* 2. Select 2nd channel on ADC (charges CHOLD to VDD).
* 3. Set sensor line to output, set low (GND)
* 4. Select sensor line as input (TRISx = 1)
* 5. Select sensor channel on ADC (V-div sensor:CHOLD)
* 6. Begin ADC conversion
* 7. Reading is in ADRESH:ADRESL
I decided to write a program for 12F676 considering these explanations.
Here is the program . Could you pls someone check the program and let me know if there are some mistakes or missed points. Because the program does not work as I want.

See Microchip AN1298 - Capacitive Touch using only an ADC
I have been using this for years without any problems.
Warning: Other compiler

Norm

[Nicmus]

Thank you Dave and Norm.
Isn’t that just “fishy”?
It looks like we got the complementary fish and learn how to fish in one strike.

Nick

[HankMcSpank]

Just in case someone was wanting to deploy a cap touch solution for fish to use - it won't work.....their enviroment is already grounded...which negates the use of cap touch under the water.....probably best going with a sealed hall effect switch, but some intensive training of the fish involved will be needed. (where to actuate, how to actuate etc)

[rsocor01]

----------------

[sumityadav]

please send me the code for capacitive touch button by using adc channel with pic16f877a controller.