Seven segment display interfacing!!!

Discussion in 'The Projects Forum' started by teen devil, Apr 22, 2010.

  1. teen devil

    Thread Starter Active Member

    Apr 6, 2009
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    I got this ckt diagram from a net source but the problem i am facing is how to control 8255 ... As i am using parallel port interfacing .... Is there any other alternate to it..
    Waiting for u siggestions.....
     
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  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    That may be one of the hardest ways to do it.

    An 8255 is an interface IC designed to be used with an 8 bit microprocessor. It has no function in this circuit. You can use one parallel port output bit to send the data and another to clock it. The parallel port is pretty much obsolete by now, so this is not a good method if you are thinking of using it in the future. What is the purpose of the display?
     
  3. teen devil

    Thread Starter Active Member

    Apr 6, 2009
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    we studying from the basics the course name is intel 8088 microproccessor so there we had topic of parallel port interfacing . so our teacher gave us project to interface through parallel ports he just want to give us the basics....
    i was thinking of this circuit to us as an indicator // for eg.. maybe i use a switch sort of thing tht when door opens it show open and same for close .. or any other sort of application ...
    there is another group of urs tht are interfacing traffic siganal sort of project it can be used there also as for stop or go for walking people.....
     
  4. teen devil

    Thread Starter Active Member

    Apr 6, 2009
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    hey if i give one bit as data and one for clock.. the seven segment will work properly ??? because i was trying to givee 8 bit data at once ... i hv calculated code for displaying HELP ...i was thinking tht if used each port of each letter wiil it work??
     
  5. beenthere

    Retired Moderator

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    The '164 IC is an eight bit shift register. To set up a display, you have to send 32 bits in a serial stream such that the correct segments end up lit.

    Use "8255" and "74164" as search term in Google to get data sheets to see how those chips work.
     
  6. teen devil

    Thread Starter Active Member

    Apr 6, 2009
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    HEY MOD... i am confused in one thing see the ckt diagram 5 v is supply which attched to all 4 of seven segments .. but which point is to be connected as all the pins from a to h are connected to 74164??????
     
  7. beenthere

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  8. retched

    AAC Fanatic!

    Dec 5, 2009
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    Common anode means all the LEDs share the 5v side and are switched with GND.
    Common cathode means all the LEDs share the GND and are switched with the 5v.

    You can choose common anode or cathode to best suit your design.

    I.E. If you are using an IC that can sink 25mA but can only source 5mA, you will want to use common cathode to sink the current through it.
    And vice-versa for common anode.
     
  9. teen devil

    Thread Starter Active Member

    Apr 6, 2009
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    ok thnx.... so it mean first i connect the common cathode tht is pin H to shift register ic and also the pin H is connected to 5 v.. am i right???
     
  10. retched

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    Common cathode should be connected to 0v(ground)

    Common anode should be connected to +5v
     
  11. beenthere

    Retired Moderator

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    When the displays all connect to the same source wire, that is the common. In the schematic you posted, that is the 5 volt line. That means they are common anode. In electrical terminology, the anode is the positive point; the cathode is the negative.

    The 74164's will also use the 5 volts as their supply. It will be important to add a .1 uF capacitor (monolithic ceramic type is good) close to pin 14 of each IC.

    By the way, those inverters shown will be 7404's. They are there to buffer the parallel port output. The resistors between the display segments and the shift registers should be 330 ohms.

    What are you planning to use for the 5 volt supply? By using "parallel port interfacing", do you mean the port on a PC? How are you planning on programming the output?
     
  12. teen devil

    Thread Starter Active Member

    Apr 6, 2009
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    Ok i got it .. I saw ur mesg now mod
     
  13. retched

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    You got it now?
     
  14. teen devil

    Thread Starter Active Member

    Apr 6, 2009
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    mod .. first i am totally messed up as far as components are concerned .. first i used multisim 10 sfter completing my schematic i converted into pcb layout in ultiboard but it shows a mesg tht resistors are virtual devices so it can not be placed here.... then i used circuit wizard there i found all thing but db 25 is missing they have 26 pin connector i confused wheter i use this connector or ... if u want to see tht schematic on circuit wizard i can post if u want ////
     
  15. retched

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    I dont have multisim, so i wont be of much help there. But if you are doing a PCB layout, you can use any 26 pin connector that has the same footprint. the copper doesnt care.
     
  16. teen devil

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    Apr 6, 2009
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    i am posting the screen shot of my circuit.....
     
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  17. rjenkins

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    Nov 6, 2005
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    As Beenthere noted earlier, a 'Parallel port' does not necessarily mean a PC printer port, and specifically when working with an 8088 CPU (or the 8080 / Z80 / 8086 / x86 generally) it can mean something very different.

    When programming for Intel CPUs, the term Port is often used to refer to an address in the processors peripheral I/O space (accessed with the IN & OUT instructions) as opposed to 'normal' program memory / data address range.

    Generically, when speaking about computers, a 'Port' can be just about any connection between a CPU or MCU and peripherals or the outside world - eg. the I/O pins on a little single chip microcontroller such as a Microchip PIC are labelled Port A, Port B etc.

    Connecting a display to a PC printer port does not seem to go well with a course on the 8088 - be sure you are doing the right thing before you spend too much time on it.
     
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