Purpose of the cap in this RC Debouncer circuit...

[keeney123]

Re: Purpose of the cap in this RC Debouncer circuit...

You will be fine. You have that curious mind and you actually enjoy what you are doing.

[Spork Schivago]

Re: Purpose of the cap in this RC Debouncer circuit...

Wow, that's cool. I was looking into using interrupts as well and putting the PIC to sleep until an interrupt-on-pin was trigged. I was told the only time I'd want to do that though is when power consumption is really important.

I've been studying the datasheet. Using more or less as reference right now. Some of it I understand real well but some of it is a bit confusing, like the prescaler stuff (until you explained it to me).

[stj]

Re: Purpose of the cap in this RC Debouncer circuit...

you really do need to read the datasheet - all 5-10meg of it.
there is a prescaler on the clock, and atleast one for the counters.


the one on the clock may interest you, you can divide-down the clock to slow down the chip and reduce it's power consumption - good for battery circuits.

[Spork Schivago]

Re: Purpose of the cap in this RC Debouncer circuit...

prescaler divides the main clock down to lower the range of the internal counters.

That's what I thought. So, if I had a timer setup, I could adjust the prescaler so one clock tick was one second? It wouldn't affect how many instructions the PIC was processing per second though, right? Just the timer?

If my PIC supports multiple timers, can I have different prescaler settings per timer? Or is it just pretty much one setting for all timers?

Thanks for all the help Stj! I couldn't imagine trying to learn this and figure this all out by simply reading the datasheet! You and Keeney123 have been a great help!

[stj]

Re: Purpose of the cap in this RC Debouncer circuit...

prescaler divides the main clock down to lower the range of the internal counters.

[Spork Schivago]

Re: Purpose of the cap in this RC Debouncer circuit...

Thanks guys. I know the KS0066 isn't the best one out there but it's the one that got sent with the kit. It's okay though, it's just a temporary thing. I believe I'm probably going to skip the 7-segment LED counter. I was thinking about it and looking around the net, I found some cd40110b counter ICs. I could daisy chain a few together and hook the buttons directly up to the x digit, 7-segment display. There'd be no need to actually use the PIC. I mean I guess I could just use the PIC to produce a clock pulse to get it to count by itself. I guess that could be kind of fun. Maybe it's time to get back to the KS0066 stuff.

Still a little confused with the timer stuff. Do you know what pre-scaler means Stj? Is it just something that controls how many clicks are in a second for the timers?

[stj]

Re: Purpose of the cap in this RC Debouncer circuit...

unused pins, you should set to inputs with pullups enabled imo.
some people like to set them as outputs, but i dont like that incase you short one to a power rail!

those switches used on pc front-panels are shit - as you found out!
but clicky switches like used on dvd players and stuff are pretty good.

btw.
http://www.microchip.com/forums/m122006.aspx

[keeney123]

Re: Purpose of the cap in this RC Debouncer circuit...

I think you got it now. I think Stj will be able to take you the rest of the way.

[Spork Schivago]

Re: Purpose of the cap in this RC Debouncer circuit...

11 pins for that.
7segments + decimal point
3 select lines for the digits.
and you need to constantly scan through the 3 digits to keep them from flickering.

that's why i prefer intelligent displays - consider an lcd with the hitchi 44780 interface instead
you only need about 7 pins and you can get one out of some junk like an old fax machine.

Right, this is just me building up to the touch screen display I plan to use. First project was to make 4 LEDs blink. Then I added buttons and made them toggle. Then I made it so when I pushed the buttons, they'd light up in binary how many times I pushed them. Now I'm going to replace the LEDs with that 24-pin 3.5 digit display. Then I'll add the Hitachi 44780 clone I have (a KS0066 I think it's called). Then I'll probably add an LCD screen and then finally, an LCD touch screen.

[Spork Schivago]

Re: Purpose of the cap in this RC Debouncer circuit...

the pic isnt really fast enough to notice a bounce - atleast the 4Mhz ones arent.

Wow. Must of been a good switch. My PIC16F628A I got running at 4MHz and I notice a lot of bouncing. I'm using a very old reset switch for a desktop PC and then a newer one from some Make: It electronics kit. The newer one doesn't bounce very much at all but the other one sure does! I mean there's still a bounce with the newer one. I need a 200 ms delay to guarantee it doesn't bounce at all. That number works for the other one as well. 100 ms for the new one catches almost all the bounce but once in a great while, a bounce was getting through. I just put a 200 ms delay in and fixed all problems.

[Spork Schivago]

Re: Purpose of the cap in this RC Debouncer circuit...

that's it.
the resistor is to stop the pin floating and should bias in the oposing direction to the switch.

So, even if I'm not using a pin, should I always set it to output or tie it into ground or something so it's not floating? Or do I just want them not floating when I'm using them later on, like with a switch, for example?

[stj]

Re: Purpose of the cap in this RC Debouncer circuit...

I found it! The website had the wrong picture listed but right datasheet! They listed some weird 10-digit LED display but I clicked the datasheet link and it really is the 3.5 digit one I have. I wonder how hard it's going to be to control. Lot of pins and I'm running out of room on my little breadboard. Might need to invest in a larger one or daisy chain a few of them together!

11 pins for that.
7segments + decimal point
3 select lines for the digits.
and you need to constantly scan through the 3 digits to keep them from flickering.

that's why i prefer intelligent displays - consider an lcd with the hitchi 44780 interface instead
you only need about 7 pins and you can get one out of some junk like an old fax machine.

[stj]

Re: Purpose of the cap in this RC Debouncer circuit...

Thanks for sharing Stj. I'll post my source after I post this question. Why didn't you have to debounce it? My understanding was pretty much all switches bounce, some more than others. SMD type ones and the smaller ones seem to bounce less than the old school ones (like the push button ones that click when you push them for a Desktop's reset button for example). Did you use hardware to prevent it from bouncing?

the pic isnt really fast enough to notice a bounce - atleast the 4Mhz ones arent.

[stj]

Re: Purpose of the cap in this RC Debouncer circuit...

Let's see if I got it right without having to look it up. Pull Up resistors pull the voltage high, right? The pull-downs pull them to ground, right? But I don't remember why I needed them enabled on the PIC now. I want to say it was for when the switch was open the pin wouldn't be left floating. I think I remember how it was bad to leave an input floating. So I enable the internal weak pull-up resistor, it pulls the pin HIGH and whenever my push buttons close, they pull it down LOW. Is that about right?

that's it.
the resistor is to stop the pin floating and should bias in the oposing direction to the switch.

[Spork Schivago]

Re: Purpose of the cap in this RC Debouncer circuit...

I found it! The website had the wrong picture listed but right datasheet! They listed some weird 10-digit LED display but I clicked the datasheet link and it really is the 3.5 digit one I have. I wonder how hard it's going to be to control. Lot of pins and I'm running out of room on my little breadboard. Might need to invest in a larger one or daisy chain a few of them together!

[Spork Schivago]

Re: Purpose of the cap in this RC Debouncer circuit...

/*
 * Project: Blinking LED
 * File:  main.c
 * Author: Spork Schivago
 *
 * Notice: Licensed under Creative Commons
 *     Attribution 4.0 International (CC BY 4.0)
 *     http://creativecommons.org/licenses/by/4.0/
 *
 * Version: 0.1
 * 
 * Notes:  Simple C program to control a PIC16F628A. The PIC
 *     will make 4 LEDs blink for a certain amount of time.
 *     The first LED blinks for a certain amount of time, then
 *     the second LED, the third, the fourth and it repeats.
 * 
 * Created on December 18, 2015, 6:59 PM
 */

/* Set the clock frequency of the microcontroller
 * to 4MHz so we can use the various delay() functions.
 */
#define _XTAL_FREQ 4000000

/* #pragma config statements should precede project file includes.
 * Use project enums instead of #define for ON and OFF.
 */

/* Configuration Bits. */
#pragma config FOSC = INTOSCIO /* Oscillator Selection bits (INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN). */
#pragma config WDTE = OFF    /* Watchdog Timer Enable bit (WDT disabled). */
#pragma config PWRTE = ON    /* Power-up Timer Enable bit (PWRT enabled). */
#pragma config MCLRE = OFF   /* RA5/MCLR/VPP Pin Function Select bit (RA5/MCLR/VPP pin function is digital input, MCLR internally tied to VDD). */
#pragma config BOREN = ON    /* Brown-out Detect Enable bit (BOD enabled). */
#pragma config LVP = ON     /* Low-Voltage Programming Enable bit (RB4/PGM pin has digital I/O function, HV on MCLR must be used for programming). */
#pragma config CPD = OFF    /* Data EE Memory Code Protection bit (Data memory code protection off). */
#pragma config CP = OFF     /* Flash Program Memory Code Protection bit (Code protection off). */

#include <xc.h>
#include <stdint.h>

/* Setup some preprocessor definitions so we can 
 * keep track of the various pins a bit easier.
 * RA0 is LED1, RA1 is LED2, RA2 is LED3 and 
 * RA3 is LED4.
 */
#define LED1  0b00000001     /* bitmask for pin RA0. */
#define LED2  0b00000010     /* bitmask for pin RA1. */
#define LED3  0b00000100     /* bitmask for pin RA2. */
#define LED4  0b00001000     /* bitmask for pin RA3. */

#define BTN_UP 0b00000001     /* bitmask for pin RB0. */
#define BTN_DWN 0b00000010     /* bitmask for pin RB1. */

volatile uint8_t sPORTA=0;     /* Shadow register to hold the state of pin
                   * to prevent RMW problem. 
                   */

void init (void);
void blink_led (unsigned char led_bit, unsigned long time_ms);
void toggle_led (unsigned char led_bit);
void delay_ms(unsigned long milliseconds);

void main(void) {
  uint8_t temp;
  uint8_t count = 0;
  
  init();

  /* Blink all four LEDs once to show the user they're working. */
  blink_led (LED1, 200);
  blink_led (LED2, 200);
  blink_led (LED3, 200);
  blink_led (LED4, 200);

  while(1) {
    if(~PORTB & BTN_UP) {
      count++;           /* Increment counter. */
      if(count==16) count = 0;   /* We only have 4 LEDs so when we reach 16, reset. */
      sPORTA = count;        /* Store count value in memory. */
      PORTA = sPORTA;        /* Update PORTA with the shadow register contents. */
      delay_ms(200);        /* Delay to give switch a chance to stop bouncing. */
      if(~PORTB & BTN_UP) {
        while(~PORTB & BTN_UP);  /* Loop until it's depressed. */
      }
    }
    else if(~PORTB & BTN_DWN) {    /* The user pressed the second button. */
      count--;           /* Decrement counter. */
      if(count==255) count = 0;   /* Since we're unsigned, negative will be 255. */
      sPORTA = count;        /* Store count value in memory. */
      PORTA = sPORTA;        /* Update PORTA with the shadow register contents. */
      delay_ms(200);        /* Delay to give switch a chance to stop bouncing. */
      if(~PORTB & BTN_DWN) {    /* If button is still pressed... */
        while(~PORTB & BTN_DWN); /* Loop until it's depressed. */
      }
    }
  }
}

/* Function to turn the LEDs on and off every second. */
void blink_led (unsigned char led_bit, unsigned long time_ms) {  
  sPORTA |= led_bit; /* Modify the shadow register (to prevent RMW). */
  PORTA = sPORTA;   /* Update PORTA with the shadow register to turn ON the LED. */
  delay_ms(time_ms); /* Wait 1s. */
  
  sPORTA &= ~led_bit; /* Modify the shadow register. */
  PORTA = sPORTA;   /* Update PORTA with the shadow register to turn OFF the LED. */
}

void toggle_led (unsigned char led_bit) {
  sPORTA ^= led_bit; /* Toggle the bit stored in led_bit. */
  PORTA = sPORTA;   /* Update PORTA with the shadow register contents. */
}

void delay_ms(unsigned long milliseconds) {
  while(milliseconds > 0) {
    __delay_ms(1);
    milliseconds--;
  }
}
/* Function to setup the various control registers
 * and set the direction of the various I/O pins
 */
void init(void) {
  CMCON = 0x07;    /* Turn comparators off and enable pins
             * for I/O functions CM<2:0> = 0b111
             */

  OPTION_REGbits.nRBPU = 0;    /* Enable the weak pull-up resistors on PORTB. */

  
  /* Set the directions of the various pins 
   * by manipulating the tri-state registers
   */
  /*   pin number
   *    76543210
   */
  TRISA = 0b00000000;       /* Set all PORTA pins to output. */
  TRISB = 0b00000011;       /* Set ports RB0:1 to inputs. */
  
  PORTA = 0;           /* Set all PORTA bits to low by default. */  
  PORTB = 1;           /* Set all PORTB bits to high by default. */
}

Sorry for all the comments. Just makes it a bit easier for me to remember stuff. My next step is to replace the blinking LEDs with a 3.5 segment display that I have. It's a 28-pin and on the side of it, it says:
ARK
SP400561N 1413

I've found other 3-segment LED displays but I haven't been able to find the datasheet for this specific one. I've found ones that look identical but are made by different companies. I wonder how much they differ...could I use a datasheet for one with the same physical measurements, number of pins, etc? The package this was in says 3-Digit Common-Cathode Numeric Display x1

[Spork Schivago]

Re: Purpose of the cap in this RC Debouncer circuit...

here is a 2button led dimmer i made years ago.
i never had to debounce it.

;*********************************************************************************************
list p=12F629 ; list directive to define processor
#include <P12F629.INC> ; processor specific variable definitions
errorlevel -302 ; suppress message 302 from list file

__CONFIG _CP_ON & _WDT_OFF & _MCLRE_OFF & _PWRTE_ON & _INTRC_OSC_NOCLKOUT

#define Speed 0x08
#define PWM GPIO,0
#define Switch1 GPIO,1
#define Switch2 GPIO,2
#define IFNZ btfss STATUS,Z
#define IFZ btfsc STATUS,Z
#define BANK0 bcf STATUS,RP0
#define BANK1 bsf STATUS,RP0
#define BeginPWM PWMFlags,0

cblock 0x20
RunDelay ; running speed of mainloop
IntCount
Dutycycle ; Holds duty cycle for PWM
w_temp ; variable used for context saving
status_temp ; variable used for context saving
pclath_temp ; variable used for context saving
PWMFlags ; variable used for software flags
endc
;******************************************************************************
;
;Code starts to run from here

Reset
goto Main

nop
nop
nop

Interrupt
goto ISRPWM



;******************************************************************************
;
; Main code section starts to run from here
Main
movwf OSCCAL
call InitPWM
call initGPIO
movlw Speed
movwf RunDelay

; The main program loop starts here. The process of PWM signal
; generation is driven by Timer0 interrupts. A software flag
; called 'BeginBWM' is set in the Timer0 ISR at the start of
; a new PWM period.

MainLoop
btfss BeginPWM
goto MainLoop
bcf BeginPWM

decfsz RunDelay
goto MainLoop
movlw Speed
movwf RunDelay


btfss Switch1 ;check the switch & goto Ramp if on.
goto Ramp_up
btfss Switch2 ;check the switch & goto Ramp if on.
goto Ramp_down
goto MainLoop

Ramp_down
movlw 0x00
addwf Dutycycle,W
IFNZ
decf Dutycycle,1
goto MainLoop

Ramp_up
movlw 0x1f
subwf Dutycycle,W
IFNZ
incf Dutycycle,1
goto MainLoop

;******************************************************************************
ISRPWM
movwf w_temp ; save off current W register contents
movf STATUS,w ; move status register into W register
movwf status_temp ; save off contents of STATUS register

; Write TMR0 to setup next interrupt interval
movlw .99
movwf TMR0
;State Machine for PWM starts from here
DecIntCount ;Decrement IntCount Register
decfsz IntCount,F ;decrement IntCount register and if it is zero then make the output pin high
goto Channel ;if IntCount register is not zero then go to chk the dutycycle of the signal
; If IntCount is 0, then it is time to start a new PWM signal period.
BeginPeriod
bcf PWM ; Set PWM output pin low

movlw .32 ; Initialize IntCount to 32
movwf IntCount
bsf BeginPWM ; Set flag for main software loop

goto ExitISR ; Goto end of ISR code


; If it is not the beginning of the PWM period, we need to compare each
; dutycycle to the value of IntCount. This is done by performing a
; subtraction and checking to see whether the result is 0. When a match
; occurs, the output pin for the PWM channel is set to 0.
Channel
movf Dutycycle,W
subwf IntCount,W ;Is IntCount - DutyCycle = 0?
IFZ
bsf PWM ;Yes, set output pin to 1


;ISR RestoreData
ExitISR
bcf INTCON,T0IF ;clear the T0IF bit in the INTCON register
movf status_temp,w ; retrieve copy of STATUS register
movwf STATUS ; restore pre-isr STATUS register contents
swapf w_temp,f
swapf w_temp,w ; restore pre-isr W register contents
retfie ; return from interrupt
;******************************************************************************
InitPWM ;Initialization for software PWM

BANK1 ;Select the RAM memory bank 1
;Timer0 assignment
movlw b'01000001' ;Select the internal clock & /4 prescaler
;0------- GPIO Pull-up Enable bit
;-1------ Interrupt on rising edge of INT pin
;--0----- T0CS->0. Select Timer mode and Internal instruction cycle clock (CLKOUT)
;---0---- T0SE->0. Select falling edge on T0CK1 pin
;----0--- PSA->0. Select Timer0 module for Prescaler
;-----001 PS2:PS0->001. Select 1:4 Prescaler rate
movwf OPTION_REG ;move the value of work register into OPTION register

BANK0 ;Select the RAM memory bank 0
;Interrupts Initialization
movlw b'10100000' ;Enable global and Timer0 interrupts
movwf INTCON

;Other Variable Initialization
movlw .32
movwf IntCount ; Initialize IntCount to 32

;Variables to hold duty cycle values
movlw .00
movwf Dutycycle

return
;******************************************************************************

initGPIO
BANK1
movlw b'11111110' ;Make GP0 as output and GP1-7 as input
movwf TRISIO
movlw b'00110110'
movwf WPU
movlw b'00000000'
movwf IOC

BANK0
movlw b'00000111' ;comparater off
movwf CMCON
CLRF GPIO ;Initialize I/O port

return
;******************************************************************************
END

Thanks for sharing Stj. I'll post my source after I post this question. Why didn't you have to debounce it? My understanding was pretty much all switches bounce, some more than others. SMD type ones and the smaller ones seem to bounce less than the old school ones (like the push button ones that click when you push them for a Desktop's reset button for example). Did you use hardware to prevent it from bouncing?

[Spork Schivago]

Re: Purpose of the cap in this RC Debouncer circuit...

The important words here are Pull UP and Pull Down.

Let's see if I got it right without having to look it up. Pull Up resistors pull the voltage high, right? The pull-downs pull them to ground, right? But I don't remember why I needed them enabled on the PIC now. I want to say it was for when the switch was open the pin wouldn't be left floating. I think I remember how it was bad to leave an input floating. So I enable the internal weak pull-up resistor, it pulls the pin HIGH and whenever my push buttons close, they pull it down LOW. Is that about right?

[keeney123]

Re: Purpose of the cap in this RC Debouncer circuit...

I'm sorry, you're right. They are and have been enabled. I just had it backwards in my head for some reason!


I decided to abandoned William Dillon's debouncer code and just go for a very simply poll the input, when we see a pin go low, register a push, wait 200 ms or so, if the button is still low, loop until it goes back high, and then continue. It's not very advanced and I'm sure there's probably some unforeseen problems that might pop up, but it seems to work my really fast button mashing and everything. I've tested it by making 4 LEDs light up in binary. One button counts up, the other counts down. No matter how fast I push the button, it seems to work just fine.

The important words here are Pull UP and Pull Down.

[stj]

Re: Purpose of the cap in this RC Debouncer circuit...

here is a 2button led dimmer i made years ago.
i never had to debounce it.

;*********************************************************************************************
list p=12F629 ; list directive to define processor
#include <P12F629.INC> ; processor specific variable definitions
errorlevel -302 ; suppress message 302 from list file

__CONFIG _CP_ON & _WDT_OFF & _MCLRE_OFF & _PWRTE_ON & _INTRC_OSC_NOCLKOUT

#define Speed 0x08
#define PWM GPIO,0
#define Switch1 GPIO,1
#define Switch2 GPIO,2
#define IFNZ btfss STATUS,Z
#define IFZ btfsc STATUS,Z
#define BANK0 bcf STATUS,RP0
#define BANK1 bsf STATUS,RP0
#define BeginPWM PWMFlags,0

cblock 0x20
RunDelay ; running speed of mainloop
IntCount
Dutycycle ; Holds duty cycle for PWM
w_temp ; variable used for context saving
status_temp ; variable used for context saving
pclath_temp ; variable used for context saving
PWMFlags ; variable used for software flags
endc
;******************************************************************************
;
;Code starts to run from here

Reset
goto Main

nop
nop
nop

Interrupt
goto ISRPWM



;******************************************************************************
;
; Main code section starts to run from here
Main
movwf OSCCAL
call InitPWM
call initGPIO
movlw Speed
movwf RunDelay

; The main program loop starts here. The process of PWM signal
; generation is driven by Timer0 interrupts. A software flag
; called 'BeginBWM' is set in the Timer0 ISR at the start of
; a new PWM period.

MainLoop
btfss BeginPWM
goto MainLoop
bcf BeginPWM

decfsz RunDelay
goto MainLoop
movlw Speed
movwf RunDelay


btfss Switch1 ;check the switch & goto Ramp if on.
goto Ramp_up
btfss Switch2 ;check the switch & goto Ramp if on.
goto Ramp_down
goto MainLoop

Ramp_down
movlw 0x00
addwf Dutycycle,W
IFNZ
decf Dutycycle,1
goto MainLoop

Ramp_up
movlw 0x1f
subwf Dutycycle,W
IFNZ
incf Dutycycle,1
goto MainLoop

;******************************************************************************
ISRPWM
movwf w_temp ; save off current W register contents
movf STATUS,w ; move status register into W register
movwf status_temp ; save off contents of STATUS register

; Write TMR0 to setup next interrupt interval
movlw .99
movwf TMR0
;State Machine for PWM starts from here
DecIntCount ;Decrement IntCount Register
decfsz IntCount,F ;decrement IntCount register and if it is zero then make the output pin high
goto Channel ;if IntCount register is not zero then go to chk the dutycycle of the signal
; If IntCount is 0, then it is time to start a new PWM signal period.
BeginPeriod
bcf PWM ; Set PWM output pin low

movlw .32 ; Initialize IntCount to 32
movwf IntCount
bsf BeginPWM ; Set flag for main software loop

goto ExitISR ; Goto end of ISR code


; If it is not the beginning of the PWM period, we need to compare each
; dutycycle to the value of IntCount. This is done by performing a
; subtraction and checking to see whether the result is 0. When a match
; occurs, the output pin for the PWM channel is set to 0.
Channel
movf Dutycycle,W
subwf IntCount,W ;Is IntCount - DutyCycle = 0?
IFZ
bsf PWM ;Yes, set output pin to 1


;ISR RestoreData
ExitISR
bcf INTCON,T0IF ;clear the T0IF bit in the INTCON register
movf status_temp,w ; retrieve copy of STATUS register
movwf STATUS ; restore pre-isr STATUS register contents
swapf w_temp,f
swapf w_temp,w ; restore pre-isr W register contents
retfie ; return from interrupt
;******************************************************************************
InitPWM ;Initialization for software PWM

BANK1 ;Select the RAM memory bank 1
;Timer0 assignment
movlw b'01000001' ;Select the internal clock & /4 prescaler
;0------- GPIO Pull-up Enable bit
;-1------ Interrupt on rising edge of INT pin
;--0----- T0CS->0. Select Timer mode and Internal instruction cycle clock (CLKOUT)
;---0---- T0SE->0. Select falling edge on T0CK1 pin
;----0--- PSA->0. Select Timer0 module for Prescaler
;-----001 PS2:PS0->001. Select 1:4 Prescaler rate
movwf OPTION_REG ;move the value of work register into OPTION register

BANK0 ;Select the RAM memory bank 0
;Interrupts Initialization
movlw b'10100000' ;Enable global and Timer0 interrupts
movwf INTCON

;Other Variable Initialization
movlw .32
movwf IntCount ; Initialize IntCount to 32

;Variables to hold duty cycle values
movlw .00
movwf Dutycycle

return
;******************************************************************************

initGPIO
BANK1
movlw b'11111110' ;Make GP0 as output and GP1-7 as input
movwf TRISIO
movlw b'00110110'
movwf WPU
movlw b'00000000'
movwf IOC

BANK0
movlw b'00000111' ;comparater off
movwf CMCON
CLRF GPIO ;Initialize I/O port

return
;******************************************************************************
END