Any tips for 4-layer boards?


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  1. #1
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    http://www.picbasic.co.uk/forum/show...=Easy+Contrast

    Actually, six years on from that post I standardised with 1K5 for R1 and 470R for R2... works well...

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    Quote Originally Posted by Melanie View Post
    http://www.picbasic.co.uk/forum/show...=Easy+Contrast

    Actually, six years on from that post I standardised with 1K5 for R1 and 470R for R2... works well...
    Errrr.... seriously? It's that easy?

    Melanie, you never fail to amaze me.

    No need for a filter cap even? Any benefit to using one?
    Any restrictions on the max/min PWM frequency?

    Thanks VERY much for that tidbit. That's excellent.

    Ahhh rats... now what am I going to do with all those digital pots I've got in stock?


    steve

  3. #3
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    Here's the HPWM code I use to drive Contrast...

    Code:
    SetLCDContrast:
    	DataA=Contrast*40
    	HPWM 2,DataA,1000
    	Return
    DataA is a byte variable. Contrast is a User software selectable value between 1 and 5. The factory default is 2.

    A Capacitor is a waste of real-estate. Your eye can't distinguish 30Hz (TV picture frame rate) let alone 1kHz as used above... your LCD probably can't switch that fast either. How fast is your LCD monitor... 3mS? - mine's closer to 9.

    As always, try it on a breadboard with your chosen LCD before you commit to PCB... I've used it sucessfully on dozens of different PowerTip and Tri-T LCD's without problems.

    If you have a couple of PWM channels, use the other one for the Backlight... same code... do a Search for Easy Backlight.

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    Thank you Melanie, that's great!

    I'll give it a try as soon as I get a chance. It saves some expense, and a bit of real estate, and 1 PIC pin compared to the digital pot method. Very nice!

    I'm already using the other PWM channel to drive a MOSFET for the backlight. I figured out how to do that several projects ago.

    I'll give your circuit a test to make sure it works with my LCD before I commit to a run of boards, but it sounds like a very happy thing for my project.

    Thanks ever so much for your help!



    steve

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    Well I just tried Melanie's "Easy Contrast" circuit and it works great!
    I tried with and without a filter cap and there's no visible difference.
    I ended up using 2K and 1K resistors because I had some laying within arms reach and it gives good control.

    That's cheaper and uses less real estate than a trimpot, and it gives the user control that I was going to use a digital pot to achieve. With only 2 resistors.

    Most Excellent! Thanks Melanie!


    steve

  6. #6
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    Default I got it all on 2-layers!

    Well, I shuffled a bunch of stuff around, made a few circuit changes, and presto!
    It all fits on 2-layers now.

    5 IC's
    19 Capacitors
    28 Resistors
    5 Transistors
    4 Diodes
    1 Crystal,
    1 LED
    + connectors and wires to the outside world.... power supply, sensors, LCD, etc.

    All on a board that's about 2.5" high and less than 2" wide.

    Thanks to everyone that provided suggestions and insight. Much appreciated.


    steve


  7. #7
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    Thats great news! Now, how are you going to solder components?

    Ioannis

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