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Shift Register circuit validity

Discussion in 'General Electronics Discussion' started by Notilix, Dec 6, 2016.

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  1. Notilix

    Notilix

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    Dec 6, 2016
    Hi!

    I'm new on this forum and in Raspberry world and electronic :)

    I'm asking there if someone could confirm my following circuit :

    [​IMG]

    In my minds, here's what is happening :
    5V external provides power for HEF4094B Shift Register and for 7 segments display.
    I connected ground together (the Pi's ground and external) to comply with the circulation rule for data communication.

    I use external power source because I don't want to use Pi's power.

    This is my first schema with Fritzing soft sorry if I did mistakes.

    Thank you for reading this
     
  2. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    You should create a real schematic with standard symbols and standard drawing conventions. Most of us here won't take the time to reverse engineer a Fritzing wiring diagram to create a schematic. Fritzing is, IMHO, for "monkey see, monkey do" efforts only.
     
    Harald Kapp likes this.
  3. Notilix

    Notilix

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    Dec 6, 2016
    Hi,

    Thank you for your answer hevans1944.

    Here's a more standard (I hope so) schema :
    [​IMG]
     
    hevans1944 likes this.
  4. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    That helps. The only possible change I would recommend is connecting OE to one of the RPi output pins and activate it after all the segment data has been shifted in and a strobe pulse has been issued to update the 7-segment display. You can also use OE as a pulse-width modulated intensity control.

    The tri-state outputs are only rated for ±10 ma, and you did not specify what the 7-segment display is. Clearly, in this circuit, it is a common cathode display with individual anode connections to each segment. You might want to consider either using a shift register with active-low open collector outputs and change the display to a common anode display with individual cathode connections to each segment, or insert transistor drivers between the latched shift register outputs and the display to allow more segment current for a brighter display.

    I have seen a similar device (with active-low open-collector outputs) to the HEF4094 used with an I2C interface to send digits to a clock display. You should have no problem adapting the RPi. And these puppies can be cascaded for multiple digit displays. Thanks for posting the circuit you are evaluating.
     
    Last edited: Dec 7, 2016
    Notilix likes this.
  5. Herschel Peeler

    Herschel Peeler

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    Feb 21, 2016
    4094 can only drive about1 mA high. What is your 7 segment display like? You might get a little brightness out of it.
     
  6. cjdelphi

    cjdelphi

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    Oct 26, 2011
    You can get a darlington array in ic dip form to compliment the shift registers output
     
  7. Herschel Peeler

    Herschel Peeler

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    Feb 21, 2016
    I had to try it to test it. Yes, it will probably drive the display as is, depending on the efficiency of the display.
     
  8. Notilix

    Notilix

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    Dec 6, 2016
    Thanks everyone I'm gonna test it soon, I just wait for another breadboard.

    I'll share my results with the forum. This is a great community
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    This is true if you want to maintain a valid logic level on the output. However the outputs are capable of about 10mA if this constraint does not need to be satisfied.

    The max dissipation per output is 100mW and for the package is 500mW. This would allow you to short 10 outputs to ground with a 5V rail.
     
    Herschel Peeler and Notilix like this.
  10. Notilix

    Notilix

    4
    2
    Dec 6, 2016
    Hi everyone.

    I finally received my new breadboard and I tested it out.

    It works like a charm! I use 330 Ohms resistors and a 4 digits 7 segments display using multiplexing.

    Very interesting experience.

    Thanks to this great community.
     
    hevans1944 likes this.
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