DIY ADC Adapter

It’s been a while since I added a blog entry, but this is worth it. This time I am building a DVI to ADC adapter so I can connect an old Apple Cinema Display to a PC.

The Backstory:
The PR department at the college I work for was going through some old stuff. They came across some Mac equipment they no longer wanted and asked my office, the Help Desk, to dispose of it properly. What came back were some Apple video cables and one 20″ Apple Cinema Display. It wasn’t the aluminum version, but the older white one that looked like an easel. Of course, this display couldn’t be connected to any regular computer because it used an ADC connector. Apple specially engineered the ADC connector so that power, video, and USB were carried along a single cable. While this was great for reducing the amount of cabling you had, it also meant you had to have either a PowerMac with a compatible video card or a DVI to ADC adapter. That originally cost an $130. Oh, don’t forget your computer had to have a DVI.

The Idea:
If you fast forward to today you can buy a DVI to ADC adapter for $75 from That would be the quick solution for connecting the monitor to a computer, but I have an idea: why not build my own? The ADC standard is basically the same as DVI with extra wires for power and USB ports. The pinout on the connectors between DVI and ADC are a little different, but shouldn’t be too hard to over come.

The Research:
Searching the Internet revealed some good information. Most of what I found discussed building a VGA to ADC adapter for the older CRT Apple monitors, but nobody had instructions for building the DVI version for the LCD monitor. Regardless most people recommended looking at the Apple development library to see the ADC pinout and spec (1). I also found a few more important articles from Apple. The Apple DVI to ADC Adapter: Compatibility Table (2) has a note that says the monitor must be plugged up to USB to have brightness, power, and sleep functions. Another page, the Apple Cinema Display Tech Specs, (3) let me know the power requirements. From all of the research I did, here was a table showing what pins would need to be connected.

Pin 1 25 V Supply
Pin 2 25 V Supply
Pin 3
Pin 4 Pin 17 TMDS data 0−
Pin 5 Pin 18 TMDS data 0+
Pin 6 Pin 19 TMDS data 0/5 shield
Pin 7
Pin 8
Pin 9 Pin 7 DDC data
Pin 10 Pin 8 Analog vertical sync
Pin 11 Pin 15 25 V Return
Pin 12 25 V Return
Pin 13
Pin 14 Pin 9 TMDS data 1−
Pin 15 Pin 10 TMDS data 1+
Pin 16 Pin 11 TMDS data 1/3 shield
Pin 17
Pin 18
Pin 19 Pin 6 DDC clock
Pin 20 Pin 22 TMDS clock shield
Pin 21 USB Data+
Pin 22 USB Data-
Pin 23 USB Return
Pin 24 Pin 1 TMDS data 2−
Pin 25 Pin 2 TMDS data 2+
Pin 26 Pin 3 TMDS data 2/4 shield
Pin 27
Pin 28
Pin 29 Pin 23 TMDS clock+
Pin 30 Pin 24 TMDS clock−
C5 C5 Ground

Included in the pile of cables that came back with the monitor I found an ADC to DVI cable. This cable was made by Belkin and was designed so you could connect a regular DVI equipped monitor to a PowerMac with an ADC connector on the video card. It did the same thing I wanted, just in the opposite direction. Still, the ADC to DVI cable allowed me do a signal test between contacts and confirm the my chart was correct.

The Parts:
To build the adapter here is what I purchased.
1x ADC connector, $3.00 (4)
1x DVI connector, $4.84 (5)
1x USB connector, $1.12 (6)
1x Power connector, $0.63 (7)
1x Protoboard, $16.85 (8)
1x 90W 24V PSU, $8.76 (9)

Total: $35.20

Other things I needed were a solder iron with very fine tip, solder, solder flux, a steady hand, and a good bit of luck.

Note: I couldn’t use a regular protoboard from Radioshack because of the hole spacing. The ADC and DVI connectors are based on the SMD (surface mount device) standard so the pins are spaced at 1.9mm. A standard hobby board has holes spaced at 2.58mm or 0.01″. The board listed above is the only one I found to be punched at 2mm and have solder pads.

The Build:
Putting everything together was tedious, but fairly straightforward. I started by installing all of the connectors onto the protoboard. This took some work because the pints were spaced at 1.9mm and the holes at 2.0mm. After a little but of wiggling everything lined up.

Now for the hard part. I had to carefully solder a wire to each of the desired pins. This was made especially difficult because of the some wires cover pins I needed access later. The solution was to solder wires on the pins closest to the middle of the board and then work my way out, attaching the wires on to the other connector when necessary.

The beginning:

The result:

With the hard part of the project the next step was to protect it from damage using a case. What project would be complete without an Altoids case. Lucky enough I had an Altoids tin sitting around for a future project. Lucky me. Using a Dremel and cutoff wheel I cut holes in the side of the case for the ADC, DVI, USB, and power connectors.

Here you can see how everything looks installed.

The Payoff:
After checking all of the input/outputs based on the chart above the only thing left was to plug in the cables. I was honestly surprised not to find any smoke rolling from the case. What’s more surprising was to see my computer detect the monitor and a picture actually show up. The screen was bright, responsive, and the colors looked good. I also connected the monitor to my PowerMac and was able to control the brightness of the backlight; something not possible from Windows 7 64-bit.

And there you have it. One working home made DVI to ADC adapter. Not bad for an amateur electronics geek.

I case your were wondering about the loose wires and red toolbox, the PSU I ordered hadn’t arrived yet so I had to use my DIY project PSU to power the monitor. It really wasn’t designed to output enough amps for the monitor, but worked for testing.


Here is a wiring diagram of the adapter. I just wish it was as easy to physically run the wires as it was in the schematic.