Plenty of older computers have only a 15-pin D-sub AUI connector for Ethernet. Apple tended to avoid this connector on Macs as it used (basically) the same 15-pin D-sub connector as the video connector, so they came up with the compact AAUI connector to use instead instead.
To connect either of these to anything that looks like a modern Ethernet cable, you need an adapter called a MAU. And while AUI to 10BASE-T MAUs used to accumulate in IT department drawers like fleas, these days they're surprisingly hard to find for a reasonable price. (Go on over to eBay and try it now...) Meanwhile, probably because they can only be used on old Macs, AAUI MAUs are easier to find for cheap. You can get 15 of them for $30 or just one for $10.
But sometimes even Mac users need AUI, as recent threads here like this one show. Is it possible to adapt an AAUI MAU to AUI?
Yes, it is. Here's a video in dazzling Potatovision that shows my adapted adapter working with an IBM PC/AT. It's hard to see the AUI connector but you can bet there's no AAUI connector there.
The AAUI connector still works if you allow the original connections to "pass through" your hack unchanged. But for AUI, it's not that simple, since AAUI usually supplies +5V power while AUI supplies +12V. The answer is to use a voltage regulator to make +5V from +12V, or what I've used myself is a cool-running buck converter like the Recom R-78E5.0 series. I've used the 1A variant, not because the EtherMac consumes 1A (nowhere close) but because I have a bunch of these buck converters handy for various projects. A hand-drawn wiring diagram is attached.
The diagram also shows capacitors connecting various "Shield" pins to ground. The standard defining AUI states that these pins must be "capacitively coupled" to Vc (which I've recklessly labeled GND) but offers no further guidance for the sake of non-wizards like me. I was not able to measure any capacitance between shield pins and Vc on a real MAU that I own, so I simply didn't fit any: the shield lines terminate on the PCB with no connection anywhere. AUI cables are allowed to be up to 50 metres long, and I'm guessing the coupling is meant to accommodate that. My ribbon cable is 5 cm long, so I'm guessing it does not matter.
To connect either of these to anything that looks like a modern Ethernet cable, you need an adapter called a MAU. And while AUI to 10BASE-T MAUs used to accumulate in IT department drawers like fleas, these days they're surprisingly hard to find for a reasonable price. (Go on over to eBay and try it now...) Meanwhile, probably because they can only be used on old Macs, AAUI MAUs are easier to find for cheap. You can get 15 of them for $30 or just one for $10.
But sometimes even Mac users need AUI, as recent threads here like this one show. Is it possible to adapt an AAUI MAU to AUI?
Yes, it is. Here's a video in dazzling Potatovision that shows my adapted adapter working with an IBM PC/AT. It's hard to see the AUI connector but you can bet there's no AAUI connector there.
The AAUI connector still works if you allow the original connections to "pass through" your hack unchanged. But for AUI, it's not that simple, since AAUI usually supplies +5V power while AUI supplies +12V. The answer is to use a voltage regulator to make +5V from +12V, or what I've used myself is a cool-running buck converter like the Recom R-78E5.0 series. I've used the 1A variant, not because the EtherMac consumes 1A (nowhere close) but because I have a bunch of these buck converters handy for various projects. A hand-drawn wiring diagram is attached.
The diagram also shows capacitors connecting various "Shield" pins to ground. The standard defining AUI states that these pins must be "capacitively coupled" to Vc (which I've recklessly labeled GND) but offers no further guidance for the sake of non-wizards like me. I was not able to measure any capacitance between shield pins and Vc on a real MAU that I own, so I simply didn't fit any: the shield lines terminate on the PCB with no connection anywhere. AUI cables are allowed to be up to 50 metres long, and I'm guessing the coupling is meant to accommodate that. My ribbon cable is 5 cm long, so I'm guessing it does not matter.
