August 15, 2011

DIY ADC to DVI converter

 A while back I was able to grab a 17 inch LCD Cinema Display from electronic surplus for 5$, while this sounds like an amazing deal, there was one extra issue that made this more fun than just being able to use it without some effort on my part.  Older Apple Cinema Displays use an ADC connector which while similar to the popular DVI, is only supported on a few older G4 towers and video cards.  Luckily I already have a working G4 mirror door with a graphics card that has the connector.  My original mod to fix the broken power supply prevents me from using the ADC connector due to lack of the extra 24v line, so with the help of my trusty heat gun, off went the connector for external use in this project to build an ADC to DVI adaptor.


First off I started looking for other people that had done this before.  While there is not a lot of information beyond a few others that have succeeded, there is a retail converter from Apple, so it is possible.

 The pinouts are quite simple to folow as ADC shares a lot in common with DVI as they are both digital. ADC Pinout and DVI Pinout.  Basically you just need to strip the dvi cable to leave just enough wire to be usable and connect the data link 1 pins, plug and play pins and digital clock pins.  The for the most part com in pairs of three (+,-,gnd)  The link 2, analog and shielding is not needed.  I also found that grounding the hot plug was required for the display port to dvi adaptor I am using to detect the monitor.  Other video cards I tested with did not need this.  The DVI spec has more information on the correct use of the hot plug pin, however I just left it grounded as the ADC spec does not include this.




The final parts needed that are not included in the DVI spec are the power and usb connections.  The monitor itself has no power supply or plug, the ADC connector needs to supply this.  I had a spare dc plug connector, so I purchased a 24v power supply off of Amazon that could supply enough amps to meet the ADC spec.  Finally there is the USB connection.  The monitor has an internal usb hub built in, also it use the USB connection to pass information about the monitor.  Unless you have the power turned on, the monitor connected and it plugged into a usb port it will not display anything!  This freaked me out at first when I started testing my solder connections and though the monitor was dead when nothing appeared with just power and the DVI connecter plugged in.




If you see weird color pixels that get better by pinching the wires together than you will need shorter leads.  It took a few tries to get the wires short enough to prevent interference.  Eventually I got it right and low and behold after connecting everything I had a clear image on the monitor.

Oddly enough right after completing this project I received a tv that can function as an external monitor so this is not as needed anymore, but I always enjoy having a few classic apple products on display.

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