Embedded Files
Along with my LCD-Upgrade (described at LVDS Single-to-dual converter Background) came a Wacom digitizer...
I've always wanted pen-input on my computer, for drawing in Gimp, etc. Marking up schematics, taking notes... maybe I'd actually learn to draw.
Since I was already messing with creating an EDID-Spoofer for the new LCD--and therefore had access to the DDC-bus--I figured it would just be a simple step to interface the tablet via DDC, and modify TabletMagic to look there, instead of an RS-232 port.
Not so lucky. Mac OS X 10.5.8 apparently has some hokey i2c implementation, which results in each byte-transaction to take *several* milliseconds. Besides being too slow for real-time tablet-data, it also *halts the computer* during transactions. (Months upon months later and I've discovered that Yep, it's in the OS code. I have yet to figure out how to recompile the kernel and kexts at opensource.apple.com. And isn't it a tad ironic that the *only* two files missing from the IOGraphics package are DDC-related?).
So, what other options? I wasn't about to run more wires through that tight hinge, though I thought about repurposing the serial port connected to the modem... I wanted something a little less hackish and more repeatable for the general public... Took a while to realize, since I'd almost never made use of it before, but Bluetooth!
Turns out bluetooth to serial converters are pretty affordable these days. Finally. So, it was done. Right?
The one I bought had a few quirks... supposedly it could be configured permanently with a specific device name, baud-rate, etc. and to go into a mode where it literally just repeats anything sent either way... So, from what I understood it should've been as simple as configuring it once and tying it directly to the digitizer.
Again, not so lucky. I'm not a bluetooth expert by any means, but it seems there's a bit to be done regarding configuration, etc. that has to happen each time it connects/disconnects. Additionally, the BlueTooth Bee (at least the version I got) seems to have a few quirks that require a reset after it's disconnected, in order to reconnect. Maybe it's something to do with the Mac, again. I dunno. I wrote an AVR program to establish a reliable means to automatically configure the bluetooth device, reset it when disconnected, to pass tablet-data through when it was connected, etc.
See the bluetooth-bee-connector Code Page
Tablet Bluetoother: Again, the PCB is mainly just used as a breadboard and breakout-board for that tiny AVR.
The ATtiny45 that does all the configuration and translation is in the upper-left corner. The blue wires go to the digitizer. The breadboard-space is nothing more than a couple voltage-regulators and a MOSFET switch. Power was originally intended to come from the EDID port, but it wasn't enough to drive the tablet. Instead, power (12V) is stolen from the LCD inverter. Oddly, this 12V is *always on* whether the laptop is powered-up or not (blew a fuse that way, no fun to replace). So the yellow-wire goes to a MOSFET switch, and is triggered by the EDID voltage.
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Also, As-Configured TabletMagic's support for this type of digitizer is only available if you have a "Hackintosh" (A PC running OSX). But that's a minor change, and I'd already been messing around with modifying TabletMagic for another purpose, so I knew what I was getting into.
Finally (hopefully), there is probably some difficulty with Sleep when it's connected, as the power would be cut to the bluetooth device. I'd intended to look into this but ultimately decided I'd rather be able to carry my laptop around with me outside the apartment... which currently would be quite a feat with the digitizer attached because the digitizer is about half an inch wider than my display's housing. I'd intended to modify the lid to accomodate that, but I don't really have the right tools for bending/cutting metal, etc.
I'd also bought an old tablet's LCD housing, which had a screen-cover, so the pen wouldn't scratch the actual LCD. I still have that attached.
End-result... it worked, and pretty reliably. The digitizer came with the LCD, I had a stylus from an OLD (486) tablet, the BlueToothBee was $15, assorted components, a screen-cover. Total cost to me: probably <$30 total. And some day I might just modify the display lid to accomodate it, or buy one of the newer digitizers that might fit...
As always, if you're interested in trying this yourself, feel free to contact me. I can send code and schematics... diffs for TabletMagic, whatnot.
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