Author Topic: Cintiq-like homebrew gfx tablet  (Read 4911 times)

Offline donM

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on: February 05, 2011, 10:24:52 PM
My journey started 3 days ago. I'm working on an animation project for 3D production class and I found out that living without a decent gfx tablet is a pain in the butt. I first thought about just making a 1024bit pressure sensitive pen but I'm not sure if it'll work well. So I decided to salvage just the cam and do everything myself.
I hope some you guys can fill me in about the precision of a wiimote cam mounted ~1m above a 22" screen! - cause if it's not precise, there is no use for what I'm planning.

OK, here's the short version of my idea:

Strip a Wiimote and grab the cam. Run the cam on highest sensitivity with a PIC18f4550 on fullspeed I2C . The PIC18f4550 has a built-in USB function which makes it ideal for my purpose especially since I can just define a new USB-HID class to submit camera and pen pressure data on USB full speed without needing a new driver and HID devices are supported by almost every software there is. I might even go for an existing experimental PIC18f board design and modify it.

My idea for the pen is to rig it with an analog pressure sensor (weight sensor ~ 5bucks @ electronic spare parts supplier). The sensor's resistance drops almost linear with increasing pressure, easy to convert to bits via the PIC's 10bit AD converter. This would allow me to get a 1024 step pressure sensitivity. I first opted to make just a pen and  use the Wiimote + Bluetooth dongle for x/y pos but I realized that encoding the whole data into a HID class would give a much higher compatibility and easier setup.

To get the data into my computer I'm planning on defining a specific USB HID packet containing penX, penY and penPressure data.
In detail there's much more stuff involved, the cam needs to be run @ 3.3volt and 25mhz clock which requires me to run 5 and 3.3 volts on my board and a 20 + 25mhz clock (the 20mhz one for the pic) but on the other hand, if I use a voltage regulator with inhibitor, I can perform a timed camera initialization which would prevent those random configs the good folks on WiiBrew were struggling with...
total cost: Cintiq = 1999   Homebrew ~ 350

well, enough tech talk, I'm looking for input!

Here's some points I need help with:

- precision: will a interpolated 1024x768 x/y resolution be enough to allow drawing on a 22" "canvas", the cam will ofc be mounted as close as possible to not lose resolution.
- calibration: I suppose I need a new calibration, well, maybe the HID joystick calib works for x/y pos, not sure about pressure though.
- ideal IR LED wavelength & pen tip: I want to help the cam calculate the position correctly which means a really bright but precise dot. Any suggestions?

If you're working/planning on a similar project or just want detailed information about the tech stuff let me know! I don't have the time to start the project right away (job/exams) but I hope to get started 'till summer.