Multiplexing 7-Segment

Hi guys,

I'm currently creating a project to learn with and it's all working except for one small thing. It uses 3 7-segment displays to basically create a counter that increases on an interrupt using a PIC16F685. I am using interrupt code from another forum post, could have been on here so I don't really understand it just yet. The rest of the code is my own as I have fiddled with multiplexing before. Here is the code I will post the problem after:

Code:

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define OSC 4
'LEDTOP        -->    PORTC.0
'LEDTOPLEFT    -->    PORTC.1       
'LEDTOPRIGHT    -->    PORTC.2     
'LEDMIDDLE      -->    PORTC.3         
 
'LEDBOTTOMRIGHT -->    PORTC.4
'LEDBOTTOM      -->    PORTC.5
'LEDBOTTOMLEFT  -->    PORTC.6
'SEG1 --> PORTB.7
'SEG2 --> PORTB.5
'SEG3 --> PORTB.6
TRISA = %11111111     
TRISB = %00000000
TRISC = %00000000
ADCON1=%00000111
ANSELH=0
ANSEL=0
CM1CON0=0
CM2CON0=0
num VAR WORD
var1 VAR WORD
var2 VAR WORD
var3 VAR WORD
num=0
DisArray var byte[10]
DisArray(0) = %01110111
DisArray(1) = %01000010
DisArray(2) = %01101101
DisArray(3) = %00111101
DisArray(4) = %00011110
DisArray(5) = %00111011
DisArray(6) = %01111010
DisArray(7) = %00010101
DisArray(8) = %01111111
DisArray(9) = %00111111
OPTION_REG = %00111000
INTCON.2 = 0
INTCON.5 = 1
TMR0 = $FF
 
On Interrupt Goto incNum
 
loop:
    var1 = num DIG 2
    var2 = num DIG 1
    var3 = num DIG 0
 
    GOSUB selseg1
    PORTC = DisArray(var1)
    pause 5
    GOSUB selseg2
    PORTC = DisArray(var2)
    pause 5
    GOSUB selseg3
    PORTC = DisArray(var3)
    pause 3
goto loop
disable
incNum:
If INTCON.2 = 1 then
 num = num + 1
 endif
 TMR0 = $FF
 INTCON.2 = 0
RETURN
ENABLE
Selseg1:
    portb = %01111111
    RETURN
Selseg2:
    portb = %11011111
    Return
 
Selseg3:
    portb = %10111111
    RETURN 
End

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It is creating a feint shadow of the 3rd segments number on the 1st segment. In other words if I make it display the number "123", it displays the number perfectly clear, but if you look closesly or in a dark room you can see the number "3" over the number "1".

I have tried fiddling with the delays but I can't get it right. Thanks :)

Ross Steytler

Hi,

I think you need to switch the port b off before going to set the segments, when you enable your port b the segments are briefly set to the previous number.

Regards
Bob...

By switching off you mean assigning it %00000000 or in my case %11111111 since it is a common cathode display?

I tried that out and still nothing, I also tried adding a small pause between selecting the other display and its still creating "shadows". Now that it is dark I see that it is doing it on all 3 segments. All "shadowing" the previous one.

Thanks for your reply

Quote:

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Originally Posted by ross246

By switching off you mean assigning it %00000000 or in my case %11111111 since it is a common cathode display?

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For common cathodes, wouldnt you need to assign 0's to the segments to blank them?

Common cathode is common negative or ground so by assigning it 0's your making it negative so switching it on

EDIT: assigning the cathode itself negative :) which is connected to portb, by assigning the segments (portc) 0's yea that would blank them.

Ah by clearing portc which is connected to the segments i have solved the problem :) thanks so much guys

Hi Ross,

Glad you got it to work. Now you can move on to not displaying any leading zero's.
Very nice code by the way, much more efficient than what I came up with a few years back.

Regards
Bob...