Counter not counting !!!

[lerameur]

Hello,

I made a small disk counter with (wheel encoder with 2 part black and 2 part white) about 2 inches in diameter. I use a light to voltage sensor. It is working pretty well at low speed, but when I flick the disk, o Maybe a few turns per seconds the counter only counts one out of the 5 turns it made. My guess is that the clocking should be made higher.. any ideas?, The whole circuit is already soldered, I hope i do not need to get it in a 20Mhz crystal.
here is the code:

' Internal Oscillation program
' A/D testing -RA.1
' LCD

'/////////////////////////
'// Define section //
'/////////////////////////

INCLUDE "modedefs.bas" 'Includes supoprt for PicBasic language
@ DEVICE pic16F88, INTRC_OSC, CCPMX_ON, MCLR_ON
OSCCON=$60 ' use internal 4MHZ osc

CMCON = 7 ' Turn OFF the comparators so pins can be used as digital I/O-pins


'/////////////////////////
'// LCD configuration //
'/////////////////////////

DEFINE LCD_DREG PORTB ' Set LCD Data port
DEFINE LCD_DBIT 4 ' Set starting Data bit (0 or 4) if 4-bit bus
DEFINE LCD_RSREG PORTB ' Set LCD Register Select port
DEFINE LCD_RSBIT 1 ' Set LCD Register Select bit
DEFINE LCD_EREG PORTB ' Set LCD Enable port
DEFINE LCD_EBIT 0 ' Set LCD Enable bit
DEFINE LCD_BITS 4 ' Set LCD bus size (4 or 8 bits) '4 therefore put wire at 4, 5, 6 and 7 of LCD
DEFINE LCD_LINES 2 ' Set number of lines on LCD
DEFINE LCD_COMMANDUS 2500
DEFINE LCD_DATAUS 250
DEFINE CHAR_PACING 2000
pause 1000


'/////////////////////////
'// PIN configuration //
'/////////////////////////

TRISA = %11100111 ' Set PORTA to all input
TRISB = %00001100 ' Set PORTB to all output
PortA = 0

'///////////////////////////////////////////////
'// Variable Declaration and initialization //
'///////////////////////////////////////////////
Output_Pot var byte
OldOutput_Pot var byte
Revolution var word
counter var byte

revolution = 0
Output_Pot = 0
OldOutput_Pot = 0
counter = 0

OldOutput_Pot = PortB.3

Mainloop:

'Calculate the distance
Output_Pot = PortB.3

if OldOutput_Pot == Output_Pot then
goto Mainloop
endif
if OldOutput_Pot != Output_Pot then
counter = counter +1 'If oldOutput_pot is different then Output_pot
OldOutput_Pot = Output_Pot
if counter =4 then
Revolution = Revolution + 1
counter =0
endif
endif

lcdout $FE,1, "Counter:",dec counter
lcdout $FE,$C0, "Revolution:",dec Revolution
pause 150


GOTO Mainloop
end

[Jerson]

Time to consider using interrupts for this. Increment within the interrupt. Keep it small and fast!! I don't recall if the 88 has interrupts on portB.3

[lerameur]

interrupt ... ok Guess I have to read up now.

[jderson]

I would suspect the "light-to-voltage sensor". Most of these have response times in the millisecond range, maybe too slow.

[lerameur]

I am not sure how interrupt can help in this case.
At slow speed the counter works, but at higher speeds it does not pick half the time or more.
I reduced the pause time to 20 after the LCDout, that did not help.

K

[Archangel]

Hi lerameur,
I would use a photo transistor and not a photocell, a Crystal or resonator running at 20 mhz rather than intosc @ 4mhz. those things might speed things up a bit. You might use interrupts to capture counts and display on an as time permits basis instead of watching every count.

[lerameur]

Hi,

I am using this little baby for a sensor
http://www.taosinc.com/productdetail.aspx?product=63

I think i will user TMR0 in my program

K