Problem using 7 segment display

[vitesse1508]

Hi all, I've tried hooking up a 3 digit common cathode 7 segment display for a countdown timer project. Having a little troublem getting this working correctly, should I be using some form of driver IC to get this working correctly? Currently using a 16F872 with a 4mhz oscillator.

I can select each of the displays and write a value to each of them separately, so presumably there is some form of driver IC required to be connected for this to work. The display I am using is this (BC56-12EWA): http://www.rapidonline.com/pdf/57-0244.pdf

Any advice would be appreciated.

Thanks

Tom

[mmotte]

tom,

You don't have to use a driver.  But you need to scan each display often.  Here is an example i tried in 2008 but was not pleased because i was using 6 7-segments and the brightness was not there. Later I did use a driver that took care of all the scanning .

#chip 16F886, 8 
#config OSC = INTRC_IO

'  Variables 
#define DisplayCount 6

#define DisplayPortA PORTB 
#define DisplayPortB PORTB 
#define DisplayPortC PORTB 
#define DisplayPortD PORTB 
#define DisplayPortE PORTB
#define DisplayPortF PORTB 
#define DispSelectA Set PORTA.0 off: Set PORTA.1 on: Set PORTA.2 on: Set PORTA.3 on: Set PORTA.4 on: Set PORTA.5 on 
#define DispSelectB Set PORTA.0 on: Set PORTA.1 off: Set PORTA.2 on: Set PORTA.3 on: Set PORTA.4 on: Set PORTA.5 on 
#define DispSelectC Set PORTA.0 on: Set PORTA.1 on: Set PORTA.2 off: Set PORTA.3 on: Set PORTA.4 on: Set PORTA.5 on 
#define DispSelectD Set PORTA.0 on: Set PORTA.1 on: Set PORTA.2 on: Set PORTA.3 off: Set PORTA.4 on: Set PORTA.5 on
#define DispSelectE Set PORTA.0 on: Set PORTA.1 on: Set PORTA.2 on: Set PORTA.3 on: Set PORTA.4 off: Set PORTA.5 on 
#define DispSelectF Set PORTA.0 on: Set PORTA.1 on: Set PORTA.2 on: Set PORTA.3 on: Set PORTA.4 on: Set PORTA.5 off
  
'The last block of constants connects the first 4 pins on PORTA to either ground (off) or Vdd (on). Each constant is a macro which is called when the matching display is about to be written to. It needs to connect all of the cathodes to Vdd, except for the one that is to be used which must be connected to ground.

'Make sure that you call the DisplayValue and/or DisplayChar routines very frequently! GCBASIC doesn't do this automatically.  
#define inchrs PORTC.3
#define incmin PORTC.4
#define incsec PORTC.2
RTCinit
'Pin Direction 
DIR PORTA OUT
DIR PORTB OUT
dir inchrs in
dir incmin in
dir incsec in

hours =0
mins =0       
secs = 5
dim Message(10)
Message() = "Hello "
Mainloop:
sayhello
secs =0
mins =0
hours =0
timeloop:
secs = secs +1 ' Increment seconds
if  secs < 60 then goto fins  ' yes, done
secs = 0  'Clear seconds
mloop:
mins = mins+1  ' Increment minutes
if  mins < 60 then goto fins  ' yes, done
mins = 0   ' clear minutes 
hloop:
hours = hours +1 ' Increment hours
if  hours < 24 then goto fins  ' yes, done
hours =0 ' Clear hours
fins: 
    'hour disp
    tens=hours/10
    DisplayValue 6,tens
    ones=hours-tens*10
    Wait 8 ms
    DisplayValue 5,ones
     Wait 8 ms   
    'min disp
    tens=mins/10
    DisplayValue 4,tens
    ones=mins-tens*10
    Wait 8 ms
    DisplayValue 3,ones
    Wait 8 ms
    'sec disp
    tens=secs/10
    DisplayValue 2,tens
    Wait 8 ms
    ones=secs-tens*10
    DisplayValue 1,ones
         
      
      'AdjustTime
      Wait 8 ms
      if  (inchrs =0) AND (incsec = 1)  then goto hloop
      if  (incmin =0) AND (incsec = 1) then goto mloop
goto fins

This was stretching scanning to the limit.  3 7-sement did not look too bad.

GL
mike

[vitesse1508]

Cheers Mike, you are spot on mate. I've altered it to use Timer1 and an interrupt to increment the time value and just had a 10ms delay between writing values to the displays and it works well :)