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Problem when connecting parallel 4 x 20 LCD display with BS2 — Parallax Forums

Problem when connecting parallel 4 x 20 LCD display with BS2

dillaindadillainda Posts: 6
edited 2011-03-31 03:37 in BASIC Stamp
Hi,


I am using basic stamp 2 on my project and I would like to display the ressult of my project to a 4 x 20 LCD DIsplay.

I am using GDM2004D, LCD Display, it is more likely very similar with common HD44780 based on this LCD specification.

I am using example code given in parallax website (attached), and following the schematic for parallel 2 x 16, no modification at all this is just to test and I just want to see if there is any output in the LCD.

I cant see any output in my LCD. I am almost frustated about this.

attached is my LCD spec code and schematic I used

lcd2x16par.pdf.GDM2004D.pdf
Parallel_LCD_2X16.bs2
bs2
bs2
Parallel_LCD_2X16.bs2
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pdf
pdf
GDM2004D.pdf
737K
pdf
pdf
lcd2x16par.pdf
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Comments

  • LloydsLloyds Posts: 75
    edited 2011-03-23 22:13
    Make sure the contrast is adjusted with the pot at pin 3.
  • dillaindadillainda Posts: 6
    edited 2011-03-23 23:11
    Lloyds wrote: »
    Make sure the contrast is adjusted with the pot at pin 3.

    I see, thank your for your reply, how much voltages that it is usually used? I am connecting pin 3 with 10K potentiometer and have tried to adjust it, but there is no difference on the LCD display.

    I will attach some photo when I am running the program when I reach home.
  • LloydsLloyds Posts: 75
    edited 2011-03-23 23:24
    Voltage at pin 3 should go from about 1 volt to 5.
    These displays can be very frusutrating to wire, and I have never done one right on the first try. I always had mistakes that I had to fix.
    Do you at least have a line of black boxes across one line? If you have the black boxes that is good because it means you probably have a wiring error.
  • LloydsLloyds Posts: 75
    edited 2011-03-24 04:07
    Again, the parallel wiring is easy to mess up, so double check everything.
    Look in the StampWorks Manual starting on page 72 about LCD displays. The info is good.
    Also, in the initialization you might try PAUSEs of 1000, 5, 1, 1. That worked for me, but i was using a 2p.
    Lloyd
  • vaclav_salvaclav_sal Posts: 451
    edited 2011-03-24 07:58
    Follow Lloyds advice - any Hitachi compatible LCD , and you got one, will run internal power up reset and will come up with first row "all dots" turned on without any other connection - just power..
    Apply power to LCD only and do not run any programs and than adjust your contrast. Now you know you got working LCD.
    There are many sample codes available, but your best bet is to get spec on your LCD and follow the initialization process sample.
    I would suggest you start with single line ( mostly default values) and than add the other options.
  • dillaindadillainda Posts: 6
    edited 2011-03-25 00:04
    Hi Lloyds and vaclav_sal.

    I have connect pin 3 with a 10K potentiometer, so when I meassured with a digital voltage meter, the voltage is varied around 1 - 5V, but I cant see any difference in the display.
    There is even no black box or dot in the first line of LCD, does it means there is something wrong with my LCD?
  • LloydsLloyds Posts: 75
    edited 2011-03-25 15:12
    So you have tried connecting pad 2 to 5 Vdc, pad 1 to gnd, with the pot connected between 1 and 2 , and the wiper of the pot connected to 3?
    Pad 1 on the LCD is the pad closest to the corner of the LCD,
    Lloyd
  • vaclav_salvaclav_sal Posts: 451
    edited 2011-03-25 17:30
    Does the LCD looks same without power connected - no change at all in brightness?

    Do you have the "Backlight supply voltage" pins connected to +5V?
    Observe polarity and note it takes whopping 150 mA!.

    Please note - you need limiting resistor of 6.8 Ohms (150ma) to be safe but it sounds too small. Of course you can make the backlight restor variable too later.
    Vaclav
  • dillaindadillainda Posts: 6
    edited 2011-03-29 23:50
    Lloyds wrote: »
    So you have tried connecting pad 2 to 5 Vdc, pad 1 to gnd, with the pot connected between 1 and 2 , and the wiper of the pot connected to 3?
    Pad 1 on the LCD is the pad closest to the corner of the LCD,
    Lloyd

    Yes, attached is the photo of my board connection.
    IMG00067-20110324-1414.jpg


    I am just following the schematic I've found in stamp work. Hmm, I am really clueless what is wrong with my LCD.
    IMG00067-20110324-1414.jpg
    1024 x 768 - 49K
  • dillaindadillainda Posts: 6
    edited 2011-03-29 23:53
    vaclav_sal wrote: »
    Does the LCD looks same without power connected - no change at all in brightness?

    Do you have the "Backlight supply voltage" pins connected to +5V?
    Observe polarity and note it takes whopping 150 mA!.

    Please note - you need limiting resistor of 6.8 Ohms (150ma) to be safe but it sounds too small. Of course you can make the backlight restor variable too later.
    Vaclav

    Yes, there is no change. There are 2 another pin for GDM2004D (pin #15 and 16) which is used for backlight, when I connect this pin with 5 dc power supply I can see the backlight, but there is still no black dot on the LCD (5V is connected with pin 2)

    I connect them with 10K resistor, I just follow exactly what is in the schematic.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-03-30 05:58
    If you've done everything right and nothing wrong, as you've insisted...
    then the LCD is bad and/or the Stamp is bad.

    Unfortunately, your pic isn't suitable for tracing your wiring with, you
    have a real jumble there.

    http://forums.parallax.com/attachment.php?attachmentid=79597&d=1301195631
  • vaclav_salvaclav_sal Posts: 451
    edited 2011-03-30 09:15
    It is still too early to say you have bad BS .

    Let's assume you have a bad LCD. (Working backlite is no quarantine that the controller works also).
    I would rip-up all your data wires ( no loss if it turns out to be bad anyway!) and leave only power/ground , contrast pot and the backlite connected.

    From my teaching experience I know that that 95% of newcomers wire the pull-up / pull – down resistors wrong. So I want to make sure of that.

    As I said before – when you apply power to LCD it goes thru internal power-up reset and than sets the display defaults to “show first line steady with all dots on “. And again – you should be able to adjust the contrast to see this line.

    Silly, but again from experience, last advice – make sure your viewing angle is correct. It is not that obvious , but some of these LCD cannot be viewed from all angles!

    When they first came on market many had a polarizing filter to correct this.

    By the way – how much current does it draw?
    With and without the backlite.
    It should be around 2ma without and plus 150ma with backlite on.

    You could do all of the above or simply spent few $ and get another LCD.
    Do not give up.
    Cheers Vaclav
  • dillaindadillainda Posts: 6
    edited 2011-03-31 03:37
    Thank you vaclav_sal and PJ Allen

    I follow your suggestion, I was just connect pin 1 - 3 today just to test if my LCD is working. This test has given negative result. There is nothing come out from my 4 x 20 LCD, that's right there is something wrong with my LCD.

    So, I just try using another LCD (2 x 16 parallel LCD) with the exact wiring as I have did before, but I try to wiring it more carefully and natty. It worked perfectly :)

    Thank you all, wah I need 1 week to just figured it out.

    DSCF7167.jpg
    DSCF7167.jpg
    1024 x 768 - 115K
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