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Thread: 16x2 LCD showing two lines of Boxes

  1. #1

    Default 16x2 LCD showing two lines of Boxes

    I am trying to make an temperature sensor, that displays the temperature on a LCD. To run the LCD I am using a PICAXE Serial LCD Firmware chip (FRM010) and a PICAXE 20M2 to run the serial outputs to the Firmware chip, then to the LCD. I tried to get it to work on a breadboard and it did, but when I try to put it on a PCB it shows me two lines of boxes, one is slightly fainter than the other. I have tried replacing the Contrast resistor, trying both a 10K and a 4K7 one. I am currently using the 10K one. I am using a MIKROE-55 Character LCD 2x16 LCD that I bought from RS online.

    Does anyone know what the problem I am having is and/or how to to fix it.

  2. #2
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    Come on, ojd233. You can at least post the code that you are using for the 20M2. Photos would help to see if your layout has some problems. Oh, and don't forget a schematic. How did you plan your wiring to the LCD?

    Welcome to the forum, but more info, please!
    - Tex
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  3. #3
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    Seeing one row of blocks usually indicates an LCD is powered but has never been initialised. This suggests that there is more to it than that. It could be that the signals between the FRM010 and LCD are mixed up or missing.

    If it worked on breadboard then it should work on a PCB. That it doesn't suggests there is some difference between the breadboard circuit and that of the PCB.

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    The Mouser website suggests by datasheet that the Mikroe-55 is in fact a Winstar LCD:
    http://www.mouser.com/ds/2/272/-364177.pdf

    The character set includes some “boxes” for higher data values.
    So are the boxes being seen:
    1. Solid boxes, or
    2. Outline boxes with or without a few inner pixels also on ?

    As already mentioned, providing schematics and clear photos of the PCB may help folks here identify the problem.

    Is the PICAXE code the same as used for your initial breadboard tests ?
    westaust55

    Hey Hamlet, 2B OR NOT 2B = $FF

  5. #5
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    Quote Originally Posted by ojd233 View Post
    I have tried replacing the Contrast resistor, trying both a 10K and a 4K7 one. I am currently using the 10K one. I am using a MIKROE-55 Character LCD 2x16 LCD that I bought from RS online.
    When you say "resistor", do you mean a trimpot (potentiometer) shown in the datasheet for your device that westaust55 has posted? I have found that, while you can get by with a fixed resistor in many cases, contrast is best controlled with a adjustable pot. If the contrast is set too high, even if the characters are transferred correctly to the module, they appear as blocks ("boxes").

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    I second inglewoodpete's quote
    contrast is best controlled with a adjustable pot
    this might not be close to the problem...but once I had a lcd on a bread board working perfect
    then after i soldered everything to the PCB...my lcd went blank because of the different voltages I used like 5vdc on bread board/ 4.85vdc on pcb
    lucky I did add a pot on the lcd so it was easy to adjust to clear view ... but it was surprising to me just a little voltage diff can change the contrast of the lcd

  7. #7

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    Board1.PNGLCD Board.PNG

    Here are the pictures of the board itself labelled. I will also attach the code.

    The code is as followed:
    low C.2
    pause 500
    main: readtemp C.7, w1
    bintoascii w1,b0,b1,b2
    serout C.2, T2400, ( 254, $80 )
    serout C.2, T2400, ( "Temperature" )
    serout C.2, T2400, ( 254, $C0 )
    serout C.2, T2400, (b1,b2,"C")
    pause 1000
    goto main

    In reply to the other questions:

    -I am using a 10K potentiometer
    -They are solid boxes, but one of the rows is slightly faded
    -I used circuit wizrd to plan my wiring, and the circuit from the FRM010 leaflet.

    Sorry for the lack of detail in my earlier post. I will try to get my schematic to you later on today or tomorrow.
    Last edited by ojd233; 04-01-2018 at 13:46.

  8. #8

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    Schematic.PNG

    There is the schematic, not sure if this completely complies with the PCB, I think I made some changes during breadboarding form

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    A schematic will be useful. Can you confirm in the left hand picture that the components at the bottom near teh red wire are a diode, a voltage regulator, and the "9V" silk-screening is an error, should be, and is, "5V".

    The boards appears to be home made so it may be worth checking voltages are as expected and there is track continuity on both boards.

  10. #10

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    The component near the red wire is a toggle switch, followed by a voltage regulator, and that annotation is incorrect, it does mean 5V. When checking the readings I get 5.01V after the voltage regulator. When I check the LCD voltage it reads 4.91.

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