Help me about drive an LCD

Discussion in 'Homework Help' started by imijoon, Jul 1, 2013.

  1. imijoon

    Thread Starter New Member

    Jul 1, 2013
    18
    1
    Hi all ,

    I needed a small 5 digit LCD but I couldn't find it . I bought a counter (like picture below) and opened it . I want to drive the LCD but I don't know how to do it . I attached the counter and it's internal board . the Via in internal board is connected to the LCD .

    please help me .

    [​IMG]

    [​IMG]
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,757
    4,800
    See that black blob? There's a custom IC under there that drives the LCD modules in such a way that it does the specific task the item was designed for.

    Digi-Key carries different 5-digit LCD displays and display modules.
     
    imijoon likes this.
  3. imijoon

    Thread Starter New Member

    Jul 1, 2013
    18
    1
    thank WBahn

    Isn't there any method to find its' protocol ? I thought it works like a multiplex 7 segment but it wasn't true . Isn't any standard to drive LCDs such this ?
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,757
    4,800
    You don't have access to the pins to even try. And if you try to get access, you will almost certainly damage it.

    It is most likely a CUSTOM module. Do you understand CUSTOM? Means that it uses whatever protocol the designer chose to use, which may well be one of their own making.

    Why do you want to set yourself up for that kind of headache when you can spend $8 and get a standard 5-digit display with a documented interface from Digi-Key or Mouser or one of several other distributors?
     
    imijoon likes this.
  5. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    I also have the similar idea that I want to using the LCD from the calculator, but this kind of the LCD that they always using pin to pin to connected to the chip(we called it black bean in Taiwan).

    Do you want to using the LCD or counter?

    If you only want to using the LCD, then you have to design the PCB by your own, if you want to using the function of counter, probably it only has two functions, you can control the reset and start/stop when you using the bjts s or mosfets or reed relays to control them.
     
  6. imijoon

    Thread Starter New Member

    Jul 1, 2013
    18
    1
    thanks again .

    I live in Iran. I have no access to Digi-key or Mouser . I have to use this because of its' size . I think although board has a blob IC but its' LCD is a standard commercial and standard commercial thing has standard protocol .
     
  7. imijoon

    Thread Starter New Member

    Jul 1, 2013
    18
    1
    I need to use just the LCD of this counter . My problem is " How can I drive it by my own AVR ? " . I don't know its' drive protocol .
     
  8. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    You could pick out the display you want from mouser and then "download the datasheet" from the link at mouser.
     
  9. WBahn

    Moderator

    Mar 31, 2012
    17,757
    4,800
    Does that display either have anything that a "normal" display doesn't have or doesn't have something that a normal display has? If so, then it is a custom display and is going to use an unknown and probably custom protocol.

    If you are lucky you can perhaps get access to the display's pins from the top side in which case you can monitor them as you change the countt and map out the segments. Keep in mind that it may be a multiplexed display.

    If you are very, very lucky you may be able to remove the display from the board without destroying it and, if you are exceptionally lucky, it will have contacts that you can connect to. That last point is becoming increasingly rare.
     
  10. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,363
    With electrical access to the COUNT and RESET inputs you can use the entire counter module as a numerical display.
     
  11. WBahn

    Moderator

    Mar 31, 2012
    17,757
    4,800
    Not very well. Think of what you have to do to count down from 99999 to 00000. The inputs are probably heavily denounced making iwhich would limit the count rate significantly - perhap to only a few dozen counts per second.
     
  12. Shagas

    Active Member

    May 13, 2013
    802
    74
    If you can get your hands on an AVR then you can probably get your hands on an LCD display . The advantage is that you will have the datasheet in front of you and you will know exactly what you are doing .
     
  13. imijoon

    Thread Starter New Member

    Jul 1, 2013
    18
    1
    fortunately I can take it apart and now I have its LCD in my hand . by help this useful link ( http://awawa.hariko.com/avr_lcd_drive_en.html ) I knew that Its driving method is direct or state LCD display drive. I could catch its pinout and attach it below . but when I try to drive It , I had some problem . for example I wanted to display number '2' in segment 3 . when I programmed my microcontroller I saw caracter 'b' displayed in segment 1 . or its display was not clear and other segments blinked .
    please help me for driving .

    [​IMG] [​IMG]
     
    absf likes this.
  14. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,363
    You cannot control an LCD by just simply sending logic signals to the pins.
    You need to send an oscillating signal to the segment while the backplane or COM signal is of the opposite phase.
     
  15. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    If you see this, it may help you to drive the LCD.
     
    absf likes this.
  16. imijoon

    Thread Starter New Member

    Jul 1, 2013
    18
    1
    I made the waveforms exactly like picture below that was mentioned in this and applys it to "com" and "segment" but "segment" doesn't light.

    please help me .

    [​IMG]
     
  17. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    How did you manage to make those waveforms, post your schematic.
     
  18. imijoon

    Thread Starter New Member

    Jul 1, 2013
    18
    1
    hi all,

    finally I can drive it and I'm very happy now. this is a film that I recorded from my display. I'm going to prepare a complete article for driving this kind of displays.

    thanks all for help me.
     
  19. imijoon

    Thread Starter New Member

    Jul 1, 2013
    18
    1
  20. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    how many "cookies" will one get when they click on your link? Why can't you post the pdf using the resources at allaboutcircuits in stead of driving people to other sites.
     
Loading...