Monday, March 5, 2012

20" iMac G4 Pro - Touchscreens

After a break, I am back and have several projects which I am starting to organize for.

1.  The 17" TMDS to DVI, including Video Tutorial has been completed.

2.  For the 17", I am thinking about finishing this up in some fashion.  This would not be an all in one, but instead may use wireless DVI and function as a second monitor.

3.  Apple Cube mod.  After searching I have seen some amazing cube mods including newer ones which use the existing heatsink.  This makes me somewhat less enthusiastic, as it has been done already, but it is still something that I would like to do using my core 2 duo ECX board.

4.  The 20" iMac G4 Pro Mod.  As I talked about in an earlier post the features that I would add to this pro mod would include, in order of importance:

A) Touchscreen: Something I have tried to incorporate since my first iMac G4 Mods
- The problems that I've had relate mostly to the fact that 20" 16:10 is no longer a common size.
- Touchscreens often add extra weight and thickness and thus complicate the designs
- Available Touchscreens are often of poor quality and use resistive technology that is not multitouch compatible and often detracts from the image by adding a reflective glare.

B) LED Backlighting: This conserves power and can allow for a much thinner LCD enclosure.
- Similar to the Touchscreen this is complicated by the odd 20" 16:10 aspect ratio.  No commercially available LED LCDs are available in this format.
- This may also allow for brightness control with a PWM control.

C) Upgraded Processor, RAM, and improved cooling: You can't have the first two without the third.
- I tried to make my previous mod as close to the original as possible, with the optical drive, space is somewhat limited and to ensure stability with the existing heatsink I went dual core i5
- To use a quad core, I will have to upgrade the cooling in place of the optical drive.

D) The native PSU: Resourceful readers have incorporated the native PSU.  
- Unfortunately, the native PSU did not fit my previous mod.  Without the optical drive and with improved cooling, I should be able to use the native PSU.

E) An iSight/Mic: Although the mic exists the rotating, tilting LCD makes the G4 ideal for an iSight.
- I do not yet know if a newer iSight will work better than the one from the iMac G5.  I already know how to turn the iSight from the G5 into a USB compatible camera, but I don't know if it will fit.

F) Aesthetic Changes: While rigs with neon lights all over were never my taste, I wouldn't mind some LED lights to differentiate this mod.

To start with, the most important thing I would like to incorporate is a Touchscreen.  Several of my iMac G4 mods have incorporated touchscreens.  I do agree that desktop touchscreens are not ideal, but in certain situations they can be quite useful.  A prerequisite is that the must be able to tilt backwards - newer touchscreen all in ones are doing this and apple's own patent shows that they have considered this approach in a design that is very reminiscent of the iMac G4 (mixed with the current iMac design).
Courtesy of
Rear View
Unfortunately, the extra girth and weight of the 20" touchscreens required significant compromise in the design.  I used a shell from an aluminum 20" cinema display and the front bezel of the G4.

At the time I hadn't yet figured out how to use the native inverter, so using the ACD solved both of these problems.  Once I figured out how to use the native inverter, I was able to use the complete original G4 shell and came to prefer the native appearance over my design despite the touchscreen.

Part of this had to do with the 5 wire resistive touchscreen which I found myself having to recalibrate frequently and had an annoying reflective glare.

However, with newer operating systems favoring touch/tablet interfaces over traditional Mouse/Keyboard, having a rotating. bending, tilting, floating touchscreen seems like the best possible type of desktop to try this on.  Lion (and even more so Mountain Lion) is actually touch friendly especially from the Launchpad interface.  Windows 8 Consumer Preview is even more touch friendly in that not using a touchscreen seems wrong.

I have an image of a broken 20" iMac G4 that will serve as the skeleton of this project.  The previous owner tore the front bezel off.  What you will notice is that the LCD comes right to the front of the enclosure.  Sure, you could put a touchscreen in front and secure it with double sided tape and the tape on the front bezel, but there would be a visible space from the side.  Plus, as you'll be moving and touching this, I worry about keeping it secure.  But, you can see that as is, adding anything in front of the LCD is difficult.

I have gone to great lengths to consider various touch options that are available, even inquired about custom touch screens.  The 20" 16:10 continues to be a difficult size to find.  There is a 20" 16:10 Surface acoustic Wave Touchscreen that I used in the past, but it requires a border that goes beyond the dimensions of the enclosure.  So that leaves these four:

Top Left is a broken 21.5" 16:9 optical touch monitor (LCD is broken by the touch aspect works).  This uses optical sensors in the corners and does require a "gap" in front of the LCD.  Can I adjust this to 20" 16:10?

Bottom Left is a 5 wire resistive touchscreen.  This is the same company that manufactured the screen for my old mod, but they have added an anti-reflective coat.  Its fairly light and thin and the correct size and ratio, but I still have reservations regarding resistive technology in general.

Top Right is an IR 19" 16: 10 touch panel.  The IR sensors are corrected in the corners and it may be possible to extend this connection.  Again, this requires a "gap" and I will likely loose touch sensing in the 4 corners.

Bottom Right is a 20" (approx 16:10) capacitive panel that I obtained from 3M.  Its an older cap active technology, but I have been playing with it on Lion and have been impressed by it so far.  While it is heavy and fairly thick, its active area fits the entire screen and as it is capacitive, multitouch drivers are available for windows (therefore should be possible for OS X).  This seems like the best solution and I feel lucky that I even found it, to be honest.

LCD enclosure
To fit it, however, I have to make the LCD enclosure itself smaller.

Show here is the LCDs enclosure.  There is a front and a back.  The LCD panel itself is quite thin and its control board actually extends outside the main enclosure.  Where it can interface with a JAE cable.
Side profile of LCD panel

Oblique Angle

 Most of the space is actually taken up by the backlight mechanism.
To be continued....


  1. Hi!

    Just want to say that i totally love your blog posts!! :)

    I have a iMac 24" alu with broken logic board, do you know if it's possible to replace the mobo with a macbook mobo? How is the lvds protocol, can i just create an adaptor cable i i have the pinout for both the imac and the macbook?

    Best regards,

  2. Billy, thank you. The biggest problem will be power. The LCD is LVDS so with a controller board you should be able to adapt the MacBooks mini display port out to send an image to the LCD . However, you'll have to power the screen including the led backlights. I've never looked inside so I'm not sure how the led backlights are controlled. As I play around with broken led displays, I should be blue to help more.

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