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Binary input Hex dispaly (7 segment LED)?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by dalmation, Aug 19, 2007.

  1. dalmation

    dalmation Member

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    Hello,
    I have a project nearly completed, but I am stuck...

    I have 8 sets of four binary output pins (8 hex characters) which I want to be displayed on an 8 character Hex display (7 segment LEDs)

    I know how to convert 1 set of four binary into 1 hex character using a decoder chip- but how do I get all 8 to display?

    The ideal solution would be individual 7 segment Led's with an integrated decoder (4 binary inputs)- but I cant find any?

    I have limited space on the PCB so the fewer components the better.

    I would be greatful for any advice- its driving me mad.

    Thanks in advance for your time.

    -DAlmation.
     
  2. kchriste

    kchriste New Member Forum Supporter

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    The old MC14495 display driver will do this. So will the Fairchild DM9368. But you'll need 8 of them.
    I don't think there are many displays with built in hexadecimal decoders/drivers available today, but they were available several decades ago. See if you can find these 5082-7340's by HP for sale somewhere:
    http://www.electro-tech-online.com/custompdfs/2007/08/HP_led_display.pdf
    A MAX6950 and a micro controller would also work. Or do it all with a microcontroller and multiplex the LED displays.
     
  3. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Last edited: Aug 20, 2007
  4. dave

    Dave New Member

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  5. dalmation

    dalmation Member

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    Okay- the HP displays are a no-no. I got a quote, $76 EACH!!!

    So I need to go down the route of a serially interfaced Display driver.
    8 individual decoders take up FAR too much space. Circuit board is limited to max 2"x5" size.


    I can just about figure out the display driver- but how do I get the 8 binary inputs (8x4 pins = 32 data pins) converted into a signal the display driver can use?

    The binary pins are not pulsed- they are on/off (high/low) constantly (obviously depending on the binary value).

    Thanks for the help so far-- I'm nearly there!

    -Dalmation.
     
  6. blueroomelectronics

    blueroomelectronics Well-Known Member

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    The TIL311 would work but also expensive.
     
  7. kchriste

    kchriste New Member Forum Supporter

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    Can you post a diagram of the entire circuit? There may be another way of getting at the data or a better design overall.
     
  8. dalmation

    dalmation Member

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    naa- wish there was a way- the binary outputs are from a different circuit and is 100% unchangable (has already been mass produced). Its the only outputs available.

    Just now I have it outputting to 32 LEDs (8 four segment led bar displays), and I calculate the binary manually into HEX. I've gotten used to it and mistakes are rare, but I really wanted an addon board that could decode it for me, but I'm limited to 1.5x4.5" circuit board size (including the led display).

    I might (at a push), be able to increase that to 2.5x4.5". Even at that- using 8 individual decoders is near impossible as I need to stick to through hole (I will be assembling myself and dont have the equipment to produce intricate surface mount boards)

    If anyone can think of something that would fit 2.5x4.5" I would jump to it.

    -DAlmation.
     
  9. Mike - K8LH

    Mike - K8LH Well-Known Member

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    Would something like this fit (four 18-pin ICs, 8 transistors, displays and resistors)?
     

    Attached Files:

    Last edited: Aug 27, 2007
  10. dalmation

    dalmation Member

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    That would certainly fit in the prescribed area and would still be quite cheap.

    I dont know much about PIC programming- but I'll read up on it now!

    Looks great! Thanks!!

    I'll probably be back shortly to pick the brains of someone who can write pic programs:D

    Thanks again.

    -Dalmation
     
  11. Mike - K8LH

    Mike - K8LH Well-Known Member

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    I would be happy to help you with the PIC program. Learning to program PIC microcontrollers can be quite challenging.

    Would you please fill in the location info' in your profile? If you're here in the states one of us state-side enthusiasts could program the PICs for you so that you don't have to invest in a programmer.

    If you have a company name you might want to register it with Microchip and then order samples of the 18-pin 16F628A, 16F648A, and/or 16F88 devices.

    Good luck. Have fun. Mike
     
  12. Mike - K8LH

    Mike - K8LH Well-Known Member

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    Forgot to ask what type of 7-segment LEDs you're using? Common Cathode or Common Anode? Single digit, dual digit, stick, etc.?
     
  13. dalmation

    dalmation Member

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    Hello,
    I started reading up on the pics on this website:
    http://www.mstracey.btinternet.co.uk/pictutorial/picmain.htm

    It's very interesting and definitely something I need (and want) to get into.
    But it is a bit much to take in on a single reading :eek:

    Your offer with the programming is very kind and would certainly be well appreciated!!

    As for my location, I'm in the United Kingdom (Scotland). I do have a pic programmer buried somewhere- I'm sure I can find it.

    The led's? Probably four double digit 7 segments, but let me check whats available- would it be easier/harder/indifferent if it was a single 8 digit display?

    Let me quickly check the pricing of whats available and get back to you- gimme 10 min (if you happen to be reading this now:confused: )

    Thanks again.

    -Dalmation

    :D
     
  14. dalmation

    dalmation Member

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    I will most likely go for four 2 digit 7seg common cathode displays. That will probably be easiest and cheapest.

    Thanks again.

    Michael.
     
  15. Mike - K8LH

    Mike - K8LH Well-Known Member

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    The only qualifier for the displays is that they should be non-multiplexed, that is they should have seperate pins for each segment and CC or CA digit connection. This a limitation of the type of multiplexing that must be used for those 18-pin PICs, an N(N-1) multiplexing or Charlieplexing scheme, which allows us to drive the displays with just 8 pins.

    A good tutorial by a Ham Radio Operator/Engineer is located here; Elmer 160 Tutorial

    I'll throw together and test the code and post it here for you next weekend. Meanwhile you should probably locate your programmer and see which PIC devices it supports. If you run into problems I suspect there'll be more than a few UK enthusiasts who'll jump in to help.

    Kind regards, Mike McLaren, K8LH
     
  16. dalmation

    dalmation Member

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    I was looking at these leds (common cathode):
    View attachment 70696.pdf

    They are about the right size and pinout.

    Another thing I meant to ask about the pic... do I need to add an external clock? If so- what frequency range is recommended. There might be a clock pulse available near the binary outputs I can tap into.

    Thanks again.

    -DAlmation
     
  17. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Most moder PICs have an internal RC clock. Stick with the 16F628A for your project.
    Another possible choice but probably a tough find nowadays would be a GAL, PAL or PEEL (no clock needed as it's just a simple logic device)
     
  18. Mike - K8LH

    Mike - K8LH Well-Known Member

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    Those displays will be fine.

    No external clock needed. We'll be using the internal oscillator on whichever PICs you procure (16F628A, 16F648A, or 16F88).
     
  19. dalmation

    dalmation Member

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    I was looking into pricing and availability for the microcontrollers...

    Are atmel microcontrollers compatible/comparable to PIC controllers, or are they a totally different animal.

    I only ask as the Atmel chips seem to be available at a fraction of the PIC cost?

    Thanks.
     
  20. blueroomelectronics

    blueroomelectronics Well-Known Member

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    The 16F628A is only about $3 qty 1 and less than $2 in slightly larger quantity. Which Atmel chip did you have in mind?
     
  21. pc88

    pc88 New Member

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    Atmel chips are not compatible but are comparable with PICs. Both lines of general purpose chips basically have the same capabilities.
     

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