Help need to build scrolling led dispaly....

Discussion in 'Embedded Systems and Microcontrollers' started by RRITESH KAKKAR, Jun 6, 2012.

  1. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    HI,

    I need to build small scale without keypad scrolling text display by using PIC starting from PIC16f676....
    I have seen it working as scanning from left right like that.

    please guide me further!!

    Thanks
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    First, select your LCD display.
     
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  3. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    I want to use LED display...
     
  4. nerdegutta

    Moderator

    Dec 15, 2009
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    What type of LED display?

    Remember that first comes the hardware...
     
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  5. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    As there are dot matrix display, ok i will use seven segment display that's fine..!!
     
  6. nerdegutta

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    Dec 15, 2009
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  7. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    OK, that will be fine...!!
     
  8. nerdegutta

    Moderator

    Dec 15, 2009
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  9. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    I don't get you, pls tell again..
     
  10. nerdegutta

    Moderator

    Dec 15, 2009
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    I was thinking you could do something like this:
    [​IMG]

    Link to big view.

    This circuit is by no means finished, but only as a clarification for what I would try to do. (Be sure to place a 0.01 uF cap near the PICs powerpin to GND. I forgot on the schematic.)

    This is just a thought. :)
     
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  11. BMorse

    Senior Member

    Sep 26, 2009
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    You can start off with the same circuit here (use the part that connects to the displays only), and just replace the PIC16F628A with your choice of pic, this display is multiplexed with 4 digits...... and can be scrolled left to right or vice versa with code, you will also have to learn about multiplexing the displays in order for you to get the desired output.....

    http://forum.allaboutcircuits.com/attachment.php?attachmentid=18943&d=1272466284
     
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  12. BMorse

    Senior Member

    Sep 26, 2009
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    That circuit will show the same digits on all 3 displays at once, there needs to be a way to select each digit to display appropriate data to it. Just a thought....
     
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  13. absf

    Senior Member

    Dec 29, 2010
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    Using 4511 decoder would also limit the display of numbers only. You wouldnt be able to show simple sentenses like "HAPPY bIrtHdAY" as shown in your youtube video.

    Allen
     
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  14. nerdegutta

    Moderator

    Dec 15, 2009
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    Yes, thought of that later in the evening...

    It is not my youtube video. I only linked to it, as a suggestion to the OP.:rolleyes:
     
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  15. MMcLaren

    Well-Known Member

    Feb 14, 2010
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    If you're using a "direct drive" design like this, you'll find you get better display brightness (better "average" current) when directly driving the cathode segments of common anode displays because the RDS(ON) for the I/O pin sinking FET driver is much lower than that of the sourcing FET driver.

    Unfortunately, "direct drive" starts to fall short, in terms of average current and display brightness, as you decrease duty cycle when adding more displays, which is one of the reasons why I came up with my MacMux method several years ago.

    [​IMG]

    Basically, the MacMux method allows re-tasking the column driver lines as <clk> and <dat> lines to load the driver IC shift registers in parallel (bit-banged parallel SPI) in about 24 cycles during a short blanking interval. The method also scales nicely for larger displays (see below) and using the PIC PWM signal to drive the </oe> and <lat> pins provides a simple mechanism for complete fade-to-black display brightness control.

    Food for thought.

    Cheerful regards, Mike
     
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  16. BMorse

    Senior Member

    Sep 26, 2009
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    You are right MMcLaren, since pics would rather sink than source, but unfortunately this counter circuit was designed for another forum member that only had common cathode display's:(. And was not paying attention when I linked to this particular attachment...:rolleyes:
     
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  17. nerdegutta

    Moderator

    Dec 15, 2009
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    Excellent! Just had time to re-read post, and it was something like this I thought of. There is a difference in the pin count on the PICs, and I thought it would make the programming easier if all the 7-seg pins where on the same port. That's why I thought of the 4511 IC.
     
    Last edited: Jun 8, 2012
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  18. BMorse

    Senior Member

    Sep 26, 2009
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    @ RRITESH KAKKAR: What kind of seven segment displays do you have, common cathode or common anode??
     
  19. BMorse

    Senior Member

    Sep 26, 2009
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    Just a thought, with that many LED matrices, why not use a matrix driver such as the MAX6952 or similar? Would reduce component count quite a bit, and does everything your circuit does.....

     
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  20. MMcLaren

    Well-Known Member

    Feb 14, 2010
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    Hi Brent,

    That's a fine chip. Nice voltage range. Lots of features. It would certainly reduce 'overhead' and the number of I/O pins required on the host mcu. A bit big and a bit pricey though, coming in around $24 a piece at Mouser, but you could probably sample one or two of them for a "one off" project. Maxim lists a hobbyist friendly 40 pin DIP package but Mouser doesn't seem to have it.

    Yep, you'd only need three Max6952 drivers ($72) for that 7*45 matrix compared to six 74HC595 drivers ($2) or six TPIC6C595 drivers ($8) and a few dollars worth of MOSFETs. Though, there would be less of a difference in component count if I were to use 16-bit constant current driver ICs. In that case I would only need three 24-pin TLC5926 or similar driver chips instead of the three much larger 36 or 40 pin Maxim chips. Of course I'd still need the MOSFET drivers. Price and component count aside, I wonder which set of drivers would actually have a smaller PCB footprint?

    As for doing everything... does it really? I don't see how you could use a proportional font with it. You're pretty much stuck with the built-in font and whatever you can do with 24 user definable characters. And what about scrolling left or right one column at a time? Or, scrolling up or down one row at a time? It kinda looks like you're stuck moving stuff one 5x7 character at a time, doesn't it? And, while 16 brightness levels on the MAX6952 is good, I typically use 64 to 100 gamma corrected brightness levels spanning 256 or more PWM steps for smooth fade capability. Finally, since the MacMux driver has control of the row or column driver lines, it's easy to form a column driven or row driven switch and/or encoder matrix using a minimum number of host I/O pins for switch matrix input. I don't see an easy way to do this on the MAX6952.

    Don't get me wrong. It's a great chip with lots of very nice features. I just don't think an economical hobbyist dot matrix moving message display is one of the applications it was intended for.

    Cheerful regards, Mike
     
    Last edited: Jun 12, 2012
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