my project Capacitive Sensing LED dimmer 12F1822 via PWM

[Heckler]

Well, After posting here a couple of days ago fishing for someone who has had success setting up the Cap Sense module on the 12F1822, and getting no response, I did some searching and was finally able to get it going.

I found a couple of threads where HankMcSpank had tackeled it... (thanks hank)
Which led to another thread where some correcttions reggarding the use of TMR0 vs TMR1.
(I can't find either of those threads now or I'd post a link)

Any way here is a little project I have wanted to do and CapSense seems to work and makes it a bit simpler.

See attached schematic.

This is the LED I am using... http://dx.com/p/g4-1-2w-108-lumen-35...b-dc-12v-51269

Which makes use of Darrel's Instant Interrupts (thanks Darrel!). You will have to go get those include files from his web site dt.cambs.net

here is the code...

'****************************************************************
'*  Name    : UNTITLED.BAS                                      *
'*  Author  : Dwight and others                                 *
'*  Notice  : Copyright (c) 2013 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 11/29/2013                                        *
'*  Version : 1.0                                               *
'*  Notes   :   PIC12F1822                                                *
'*          :                                                   *
'****************************************************************
#CONFIG
  __CONFIG _CONFIG1, _FCMEN_OFF & _FOSC_INTOSC & _WDTE_SWDTEN & _MCLRE_OFF & _CP_OFF & _IESO_OFF & _BOREN_OFF & _PWRTE_OFF
  __CONFIG _CONFIG2, _LVP_OFF
#ENDCONFIG

DEFINE  OSC 8                'tell picbasic what speed the oscillator is

INCLUDE "DT_INTS-14.bas"     ' 
INCLUDE "ReEnterPBP.bas"     ' Include if using PBP interrupts

OSCCON = %01110010         
                        '0 = 4x PLL is disabled
                        ' 1110 = 8 MHz 
                        '     0 = unused
                        '      1X = Internal oscillator


ANSELA = %00000100        'make port A.2 is analog
TRISA  = %00000100        'port A.2 is input
WPUA   = %00000000        'turn off weak pull ups

APFCON = %00000001        'Alternate Pin Function Control Reg (default %00000000)
                          'move CCP to PortA.5 (for PWM output)
OPTION_REG = %10000111     
                        '1 = All weak pull-ups are disabled (except MCLR, if it is enabled)
                        ' 0 = Interrupt on falling edge of RB0/INT pin
                        '  0 = Timer0 clock is internal cycle clock (Fosc/4)
                        '   0 = Increment on low-to-high transition on RA4/T0CKI pin
                        '    0 = Prescaler is assigned to the Timer0 module
                        '     111 = 1:256 Timer0 prescaler rate
                
T1CON = %11000001       'enable timer 1 (bit 0) & source the clock from the CPS module (bit 6 & 7 =11

CPSCON0 = %10001100     'set the CPS module highest frequency availabe (for vcc mode) + timer0 clock sourced from CPS module. (BIT 1)
                        '1 = CPS module is enabled
                        ' 0 = CPS module is in the low range. Internal oscillator voltage references are used.
                        '  00 = unused
                        '    11 = Oscillator is in High Range. Charge/Discharge Current is nominally 18 µA
                        '      0 = Capacitive Sensing Oscillator Status bit (only readable)
                        '       0 = Timer0 clock source is controlled by the core/Timer0 module and is FOSC/4

CPSCON1 = %00000010        '0010 = channel 2, (CPS2)

CM1CON0 = 0   ' COMPARATOR OFF
CM1CON1 = 0   ' COMPARATOR OFF

CPS2_PRESENT    var WORD
CPS2_THRESHOLD  var WORD
CPS2_LAST       var WORD

'       Software variables
'       ==================
Duty    VAR WORD
stepp   var byte


' ----------------[ I/O Definitions ]-----------------------------------
FET VAR PORTA.5  ' PWM output to control the FET switch

'       Software/Hardware initialisation
'       ================================
PAUSE 50                           ' OSC settle delay
Duty = 0
stepp = 5
hpwm 1,255,250                     ' Start with Light full ON
pause 1000
     
ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR0_INT,  _Timer0_Int,   pbp,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM
 
TMR0 = 0                  'clear  TIMER0
@ INT_ENABLE  TMR0_INT    'enable timer0 interrupts
'***********************************************************************
'------------------------------< Main program >-------------------------
Main:
pause 100   ' not a whole lot going on here
goto main

'*****************************************************************************
Timer0_Int:
@ INT_DISABLE  TMR0_INT   ' stop timer0 interrupts while we're in here
pause 25

CPS2_PRESENT = TMR1                                ' take a snapshot of Timer1's present count.
CPS2_THRESHOLD = CPS2_LAST - ((CPS2_LAST/10)*2)    ' this sets the 'trigger' up for a 20% diversion (finger press)
CPS2_LAST = CPS2_PRESENT                           ' store away the present timer0count for the next time we come into the interrupt routine

if cps2_present < cps2_threshold then
    stepp = stepp +1
    if stepp>6 then stepp=0            ' check for rollover
    lookup stepp, [0,1,16,64,128,255,255],duty  'choose level, 5 levels plus OFF
    if stepp=6 then 
        hpwm 1,0,1000    'off              ' arrive here when brightness is MAX
        pause 100                          '    So blink to let user know.
        hpwm 1,255,1000  'on
        pause 100
        hpwm 1,0,1000    'off
        pause 100
        hpwm 1,255,1000  'on              ' blink to show that you are at the highest level
    endif    
    hpwm 1,duty,250                    ' else set new level                       ' button pressed so increment stepp  
    pause 100
endif

pause 50      
TMR0 = 0                  ' clear TIMER0    
TMR1 = 0                  ' clear TIMER1
@ INT_ENABLE  TMR0_INT    ' re-enable timer0 interrupt
@ INT_RETURN   

end

enjoy! and tell me what you think (good or bad)

[Demon]

I like your PIC power supply. What is the expected life of that zener? Little current = forever?

Robert

[Heckler]

I didn't know that zeners had a limited life span.

One thing that did occur to me (during the night ) is that this type of power supply would limit the PIC's ability to provide a "high" output with any amount of current. So if you want to use those pins for something else you would want the active state to be a LOW or ground, or change the value of the 10K resistor to a lower value.

I did measure the current draw at 0.9 ma.

I designed this to specifically be an emergency light or camping light so I wanted the PIC to draw as little power as possible in the OFF state.

With a 7 amp hour gel cell it should last quite a while drawing only 1ma.

[Demon]

I didn't know that zeners had a limited life span.

...

I don't know, that's why I'm asking. I've thought of this idea before but didn't know if it was reliable, or what the limitations were.

I kept thinking it was too simple to be true and wondered why I didn't see anyone else doing it.

Robert

[Charlie]

I don't know, that's why I'm asking. I've thought of this idea before but didn't know if it was reliable, or what the limitations were.

I kept thinking it was too simple to be true and wondered why I didn't see anyone else doing it.

Robert

This approach is often used as a voltage reference, but rarely as a power supply because it's very inefficient and has lots of other issues. You need to size the resistor so the voltage across it does not cause a troublesome dip in the VDD voltage at peak currents. Typically, you would need to have about 10x the current the PIC needs flowing all the time in the zener. A much more robust approach would be to put this circuit to the base of a NPN transistor, with the collector on the supply rail and the emitter on VDD. Then you can reduce the quiescent current consumed by roughly the gain of the transistor.
Anyway, this circuit is fine for a demo or an application where there's lots of free current. Of course, every time the PIC takes a sip of current, noise is induced on VDD. Maybe it doesn't matter - but anything with an ADC using VDD as reference won't be happy. Note it will have a much better sense of humour with a big cap across the zener for those computational gulps of current. Of course, then it will come up slowly, which might cause other issues. In the end, a 3 terminal regulator is the easiest, and may even be the cheapest solution.

[Demon]

...

One thing that did occur to me (during the night ) is that this type of power supply would limit the PIC's ability to provide a "high" output with any amount of current. So if you want to use those pins for something else you would want the active state to be a LOW or ground, or change the value of the 10K resistor to a lower value.

...

What if you just used VDD (pin 1) as your source, couldn't you then do as you please with that "regulated" 5V?

Edit: ok, I see where you're going. Even using a transistor on the pin, you're still limitted by what can pass through the resistor.

What if you use a higher wattage resistor?

Glue a heatsink on it.

Robert

[pedja089]

I would use LDO with low Iq, eg. tps709135
And put pic in sleep, wake up with timer interrupt, do things, back to sleep...
This way you can get average current very low, under 100uA.

[Heckler]

Wow, I didn't know they made voltage regulators with that low of idle current.

My intention was to be able to leave the ckt connected to a, say 7 Ah, gel cell battery for at least a few weeks.
I will probably add to the circuit board a jumper or small switch to completely disconnect the ckt for storage. Even 1 ma will use up 8.76 Ah in a year. Probably not much more than the self discharge of the batt, though.

For a hobbyist though the junk box is your friend. That regulator is a bit esoteric and the shipping cost would drive up the cost for just a few items.

If you study Zener regulator ckts they are somewhat inneficient if your current needs vary by much. This ckt would get below 2 volt if the current draw gets over 1ma with a 12V source. Since my ckt pulls a bit less than that I am OK. Actually now that I look at it I may want to lower the 10K resistor to say a 5K or so. It's all just experimentation at this point.

If one wants to be able to draw more current for the other PIC pin outputs then it quickly becomes necessary to use a lower value resistor.

I'm sure a good electronics engineer could shred this idea for any kind of commercial application.

Mostly I was determined to get the Cap Sense working and be able to evaluate its suitability for other applications.
Sometimes I just enjoy the challenge of figuring out these Little PICS and what they are capable of. They truly are amazing what is in these little packages for such a few dollars.

For example the APFCON register. It allows you to move the function of some of the PIC peripherals from one pin to another if needed!! (which I did need to do with the PWM from A.2 to A.5)

[visnja30]

Hi,
if someone can explain how using the program of Mr. Heckler to make that ports A.0, A.1, A.3 be the same as the touch sensing port A.2
For example, when I touch the port A.0 then lights are increases , and when I touch port A.1 to reduce the light LEDs.
I do not understand how to run the port A.0 and A.1 to be a touch sensor.
Best regards

[Heckler]

If you look at the datasheet for the 12f1822 you will see that only pins A.0, A.1, A.2 and A.4 have cap sense capability.
You will have to work with those pins.

Also, as Charlie and others have pointed out, I would not do the Zener regulator. It is inefficient and does not allow one to draw more or less current as your circuit might demand, at least not efficiently.

The Zener regulator idea was a bad one... especially with the LDO regulators available for about the same cost and parts count.

[visnja30]

My mistake,I mean portA.4 but wrong I write on post.

[Heckler]

Have you been able to get the circuit and/or code working as I posted above?

Once you get it working as posted then you can work on getting other features and customize it as you want.

Right now each time you touch the cap sense pad it changes the LED brightness using PWM

[visnja30]

Hi,
today I receive a free samples from Microchip and I got a big surprise.My EasyPIC5 development board can not program PIC12f1288 so I can not to try your code.
I have another PIC16f724 with capacitance sensing module But I dont have a working example for him.I try to adjust your code to PIC16f724 but I have a error while compiling.

ASM ERROR symbol not previously defined (TMR1) (0) error 113

When I compiling your code for 12F1288 I dont have this error.

[RWright]

Hello again,
I got rid of my problems with the touch reliability by greatly reducing the pause times in the main part of the program. However, I would like the 1/0 button to be a latch function and not toggle as it is now. I've tried all sorts of things, but they interfere with the interrupt, or they only work once, and none of the buttons work again. Any help would be greatly appreciated. Thanks.

[richard]

RWRIGHT
If you put yourcode in code tags its then much easier for us to examine it properly

this is the way i scan mutiple keys , not sure if your chip has a T1GATE_INT but if it has it makes life easy.

isr's are best kept short and simple .

'****************************************************************
'*  Name    : CAPSENSE.BAS                                      *
'*  Author  : RICHARD                                           *
'*  Notice  : Copyright (c) 2011 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 10/20/2011                                        *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          :      12f1822                                      *
 '                                                              *
'****************************************************************
 
'#DEFINE DBUG 1                            
#CONFIG
   __config _CONFIG1, _WDTE_ON    & _FOSC_INTOSC   &_MCLRE_ON    &_PWRTE_ON 
   __config _CONFIG2,              _LVP_OFF 
#ENDCONFIG

include "dt_ints-14.bas"
include "REENTERPBP.bas"
Include "modedefs.bas" 
asm

INT_LIST macro
      INT_HANDLER T1GATE_INT, _TB1, PBP,YES
      endm
      INT_CREATE
ENDASM
 
@Timer1=TMR1L 
 THRESH CON 4000   'mult by 4 for 4mhz clk
 CNT VAR WORD   'TIMER1 OUTPUT
 FLG VAR BYTE    'GOT A KEY 
 KP VAR BYTE     'WHICH KEY
 Timer1 VAR WORD EXT 
 PW  VAR WORD   ; PULSEWIDTH
 
DEFINE OSC 16
DEFINE DEBUG_REG PORTA
DEFINE DEBUG_BIT 0
DEFINE DEBUG_BAUD 9600
DEFINE DEBUG_MODE 0             
        
        
   OSCCON=$7a       '16mhz int osc
   CPSCON0 = %10001100      'high range
   CPSCON1 = 2 'cps ch 2
   WPUA   = %00000000 
   ANSELA=  $14    'an4 ans an2 activated
   TRISA =   %011110      'gpio.0 output
   OPTION_REG=$C7      'edge int. prescale 1:256
   PIE1.7=1   'timer1 gate interrupt
   T1GCON=$E1    ' single shot timer0 overflow as input
   T1CON=%11000101   'capsense as input no prescale no sync
   INTCON= $C0       'peripheral interrupts
   PW=512
   APFCON.0=1
   LATA.0=1
   t2con=7 
   
  
    
#IFDEF  DBUG 
    LED VAR LATA.5
    LED=1 
    pause 2000
    Debug "Start",13 ,10
    LED=0
    pause 500 
#ENDIF 
   ccp1con=12
   CCPR1L=128

 FLG=0 
  
 
 
MAIN:
    IF FLG.1=1 THEN 
        IF KP = 2 THEN
           PW= (PW+64)  MIN 1023
        ELSE     'MUST BE THE OTHER ONE    
           PW = PW-64
           IF PW.15 THEN PW=0 
        ENDIF
        CCPR1L = PW>>2;
        ccp1con=12|((PW&3)<<4);
        #IFDEF  DBUG 
            debug #CNT,9,"KEY ",#KP,13,10 
            debug #PW,13,10 
        #ENDIF
        PAUSE 300
        PIR1.7=0 'clr   int flag
        FLG=0       'clr    key pressed flags
    ENDIF
GOTO MAIN 
 
            
TB1:
 T1CON.1=0 'DISABLE TILL REQ
 ;LED=!LED
 CNT=TIMER1

 IF CNT <  THRESH  THEN    '   KEY DETECTED  
  FLG.1=1
  KP=CPSCON1 
 ENDIF 
 CPSCON1  =CPSCON1  ^ 1    ;check next key  CPS2 OR CPS3
 TIMER1=0

 T1CON.1=1       'CLEAR ALL AND START AGAIN
@ INT_RETURN

[RWright]

Thanks for the info! Unfortunately it doesn't appear that my chip doesn't have the T1GATE_INT.

[richard]

Thanks for the info! Unfortunately it doesn't appear that my chip doesn't have the T1GATE_INT.

correct "does not" " does not" means it has one

if your using the chip mentioned in your first post then I suggest a closer read of the data sheet is in order . I can see a T1GATE module

I am using a PIC16LF722A for the micro.

[RWright]

LoL! Double negatives always get me. I got up from the computer when I was replying earlier. Sorry. Also, it isn't the PIC18F22, it is the PIC16LF722A. I think I dragged some info from the original post that I was commenting on because I had incorrectly posted. The original post was by Dwight and Others. My touch scanning seems to be working good now, except I want the I/O button to be single step, and still keep the up and down button in a repeat mode as it is now. Thanks again in advance.

[RWright]

Hello again,
I'm still not seeing anywhere in the datasheet or device files a reference to the T1GATE_INT. I see a timer1 gate function, is this what you mean? Sorry about the listing in the content of the posting. How do I put
it in the code tag? The I/O button is indeed a power on/off, but only in the sense that the pwm is full on or full off. I would like to be able to stop the code from repeating if the 1/0 button is pressed, until it has been released
and then pressed again, only in a single-shot manner. Thanks again.

[mackrackit]

Code tags...

When you click reply to thread a basic reply dialog shows. At the bottom right there is an Advanced button. That will take you to a full editor.
Look for # in the toolbar.

[RWright]

Hello again.

What is happening with CPSCON1 =CPSCON1 ^ 1? Is the THRESH a fixed value predetermined? Just wondering where the THRESH CON 4000 comes from. Thanks.

[RWright]

Hi again,

It does appear to be simpler when you know what you are doing! What is happening in the ccp1con=12|((PW&3)<<4) statement? Thanks again.

[HankMcSpank]

Well, After posting here a couple of days ago fishing for someone who has had success setting up the Cap Sense module on the 12F1822, and getting no response, I did some searching and was finally able to get it going.

I found a couple of threads where HankMcSpank had tackeled it... (thanks hank)

You are welcome ;-)