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Author Topic: Need multiplexed 7 segment document  (Read 3647 times)
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MAXPAYNE
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« on: January 23, 2008, 08:13:23 08:13 »

I need some documents to know "how multiplexed 7 segment display operates"

Do u have any Huh
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Silent_Thunder
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« Reply #1 on: January 23, 2008, 09:14:29 09:14 »

hi MAXPAYNE
Attached is a simple schematic witch was part of a project.
it shows how to connect the digits in a multiplexed way.
hope that answers your question

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ashu.spect
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« Reply #2 on: January 23, 2008, 09:34:35 09:34 »

This is the multiplexwd 7-seg LCD i have used with PIC

Ashu
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MAXPAYNE
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« Reply #3 on: January 23, 2008, 08:19:40 20:19 »

I need some documents as i have to prepare a report on this topic....
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localcrack
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« Reply #4 on: January 23, 2008, 08:29:48 20:29 »

Use Charlieplexing - Reduced Pin-Count LED Display Multiplexing

http://www.maxim-ic.com/appnotes.cfm/an_pk/1880
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MAXPAYNE
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« Reply #5 on: January 23, 2008, 08:33:14 20:33 »

I don't need charlieplexing description. only multiplexing method in ICM7217 display output
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Trishool
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« Reply #6 on: January 24, 2008, 07:21:26 07:21 »

I don't need charlieplexing description. only multiplexing method in ICM7217 display output

MAXPAYNE , You need to understand what multiplexing is .I would quickly sum ups as , in a 7 segment display all the LEDs are named a,b,c,d,e,f,g for each digit say four "8888" . Now all the 'a' are connected in parallel wit 'a' and 'b' with 'b' and so on till 'g' . And they have common LED anodes (cathodes are also there) which supplies voltage to only one digit OK. This way if you want to display say 1234 , first you glow f,e pins(refer to ICM7217 page 9-22) of all the 4 digits , BUT supply the anode voltage to only the first digit ,wow you can see 1 written on the display. Since you also need  2 now you withdray connection from first digit anode and its alpha digits , and supply the logic a,b,g,e,d and this time supply connection to second digit anode and so on . This process is repeated with very fast speed and our eyes are not able to distinguish the on/off time generated by the multiplexing procedure.

Ts   
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DINESHjp
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« Reply #7 on: August 18, 2008, 04:26:17 16:26 »

hi ,this sample pro gramme will give u  the idea of multiplexing.
 the pro gramme is written in basic for bascom compiler

'  file: 7SEGMENT.BAS
'  demo: how to use a 7 segment display mutiplexed using TIMER0
'  *TIMER1 is used for RS-232 baudrate generator
' The 7 segment displays are connected as following
' 7 SEGMENT    PORT PIN    value
' a             P1.0        1
' b             P1.1        2
' c             P1.2        4
' d             P1.3        8
' e             P1.4       16
' f             P1.5       32
' g             P1.7      128
'number 0 will be : a+b+c+d+e+f=1+2+4+8+16+32=63
'1 = b+c=2+4=6
'2=a+b+g+e+d=1+2+8+16+128=155
'3=a+b+c+d+g=1+2+4+8+128=143
'well the rest I leave up to you !
' The common can be common cathode or common anode
'This example uses common cathode so making one of the displays common 0V, will
'show the segments when the signals on P1 are positive
' Common 1     P3.0  MSB
' Common 2     P3.1
' Common 3     P3.2
' common 4     P3.3  LSB
'--------------------------------------------------------------

Dim Gt As Byte , L As Byte , Char As Byte , Disp As Byte , S As String * 5 , Z As String * 5

Config Timer0 = Timer , Gate = Internal , Mode = 2
'Timer0 = counter : timer0 operates as a counter
'Gate = Internal  : no external gate control
'Mode = 2         : 8-bit auto reload (default)

On Timer0 Timer_0_int
Load Timer0 , 100                                             'when the timer reaches 100 an interrupt will occur
Enable Interrupts                                             'enable the use of interrupts
Enable Timer0                                                 'enable the timer


Rem Setting Of Priority
Priority Set Timer0                                           'highest priority
Start Timer0                                                  'start the timer


Do
  Gt = Gt + 1
  Wait 1
Loop                                                          'loop until users enters 1

End


Rem The Interrupt Handler For The Timer0 Interrupt
Timer_0_int:
  'we will display the valueof gt on the 7 segment displays
  P3 = P3 Or 15                                               'all displays off
  Disp = Disp + 1                                             'which display are we doing?
  If Disp > 4 Then Disp = 1

  S = Str(gt)                                                 'for example 123
  L = Len(s)                                                  'get the length of the string
  L = 4 - L
  Z = String(l , 48)
  Z = Z + S                                                   'add leading zeros


  mov r0,#{z}                                                 ; address of string
  mov a,{disp}                                                      ; value of disp
  dec a                                                       ; adjust
  add a,r0                                                    ; add to a
  mov r0,a                                                    ; address of character
  mov a,@r0                                                   ; get into acc
  subb a,#48                                                  ; strip ascii
  P1 = Lookup(acc , 7seg)
  If Disp = 1 Then
     Reset P3.0
  Elseif Disp = 2 Then
     Reset P3.1
  Elseif Disp = 3 Then
     Reset P3.2
  Elseif Disp = 4 Then
     Reset P3.3
  End If

Return


'here we store the values that will be assigned to P1 to show a number
'dont forget to add the other digit values!
7seg:
Data 63 , 6 , 155 , 143
« Last Edit: August 18, 2008, 04:27:16 16:27 by DINESHjp » Logged
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« Reply #8 on: September 10, 2008, 08:49:10 08:49 »

@Maxpayne,
7 segment display multiplexing is using the inertial vision factor of the humans. It means the humany eyes do not recognize the changing of the frames less that 25 frame per second. If you cahange the vision frame 20 times per second you cant understand that it was changed.
After this small explanation lest look how it can be done.
First of all we need to look the specifications of the system;
- All the segments are connected in paralell. It means, all (a) segments , all (b) segments  and all other (c)-(d)-(e)-(f)-(g) segments has been connected to each other.
- The system can work as common anode mode or common cathode mode. Each common pin must be controlled seperately.

Lets consider we have 4 pcs. 7 segment display and we would like to display on them 1-2-3-4 figures . (4 will be on the most right display which will be called as first display)
- at the beginning all the segments are off by the common anode pins (or common cathodes)
-  We give the 4's informations to the 7 segment lines and open (display on) the common anode (or common kathode) of the first display . We see immediately the 4 figure on the last display. We keep it there about 1-10 ms. and turn off the display again by the common pin.

- We give the 3' information to the 7 segment lines and open the  second display again by the common pin. We will see on the second display the 3 figure, kepp it there again 1-10 ms. and turn off the display.

- we give the 2's information to the third display and open the display by common pin keep there the information 1-10 ms. and turn off the display.

- we give the 1 's information to the 7 segment line and turn on the fourth display and keep there the information 1-10 ms.
AFter completing this cycle we have to start from th ebeginning again.
By this system you can see 1234 figures on the displays and you can not understand that they are changing (on-off).
The main idea is to make a calculation as which periode you keep each figures on the displays. 1 second=1000 ms. and if you divide it to 25 you find 40 ms whichis the total time for changing all the displays. We have 4 display and if we divide 40 to 4 we find 10 ms. It means each display should keep the information at least 10 ms. This is the practical calculation of the keeping time.
I hope you understand somethings.

Ero

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MAXPAYNE
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« Reply #9 on: September 10, 2008, 03:34:05 15:34 »



Here is a animation of multiplexing technique from http://www.hobby-elec.org showing "382"

I think this will ease the method for the newer........


 Cheesy Cheesy Cheesy
« Last Edit: September 10, 2008, 03:35:50 15:35 by MAXPAYNE » Logged

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