Posted by & filed under DIY Cintiq.

After carrying out a lot of tests on the Samtiq and finding problems with the jittering I started to shield various parts of the unit to see if that remedied the problem. Here is the extension cable which runs from the controller to the column drivers on the LCD. I have wrapped aluminum foil around the cable and in this shot I am part way through wrapping it with electric tape:

shielded_controller_cable

Here is a close up:

shielded_controller_cable_closeup

It was a bit tricky to shield the row and column drivers so I decided to wrap aluminum foil around the tablet instead. This is ok in my case because the tablet reading height is 25mm and I can leave the tablet in its case.

tablet_foil_wrap

Once I had covered all the non-active area of the tablet, I wrapped a layer of tracing paper over the top to insulate the LCD from the aluminum foil:

tablet_tracing_paper_wrap

With these tests I decided to use the DVI input of the monitor and I think that helps, I dont have any jittering problems at all. The tablet seems to work great except when the pen is lifted off the surface to a height close to its reading limit. In this situation the tablet will sometimes register false clicks, they seem to occur close to the middle of the screen but not the same spots all the time. This is very annoying and seriously affects usability, I did a lot of tests without much success, here are some of my findings:

    1. lower refresh rates seem to help, but not a huge difference. Min tried was 60Hz
    1. shielding and moving the controller/inverter did not seem to make any difference
    1. unplugging both backlights tubes didnt make much difference
    1. shielding the row/ column drivers don’t seem to make much difference
    1. grounding the shields on the tablet, controller cable didn’t make much difference

    1. wrapping foil around the pen except the tip, disables the pen! :)
    1. filling the background in photoshop with black made the inteference worse!

This last point indicates that it is actually the liquid crystal unit which is intefering with my tablet (wacoms may be different). To display black the LCD has to supply power to a bunch of pixels so that they stop light passing through, this voltage is interfering with the tablet.

I am very close with this project but yet so far…. everything is working except when the pen is lifted. I am wondering if UC-Logic uses a special pen for their tablet modules which is not as prone to the inteference from the LCD. Or maybe they specify to the developers what LCDs are suitable for use with their modules. I would love to get some more info about this.
In the meantime I might have to keep sliding my hand across the LCD. :)

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