Something old, something new, and a KVM for the two

August 30, 2019 9:30 AM

What KVM and related cords will I need to get to share a USB-A keyboard, USB-A mouse, and old-school DVI monitor between a late 2012 Mac Mini and a 2019 Macbook Air?

I'm flummoxed by the choices and expect there's going to be some Frankenstein adapters involved.

• The monitor is ancient but serviceable. It has only one input source, DVI-D(?).
• Currently the monitor is directly connected to the Mini via a DVI-to-mini-displayport(?) adapter. The adapter works fine and I suspect will be a part of the solution.
• The Macbook Air has exactly two USB-C ports and nothing more. One of these ports is used to power the thing, and using it unpowered is not preferred.

I think the hard bit is going to be the video. My suspicion is that it's going to be impossible to find a KVM that can switch between a mini-displayport input and a USB-C input.

An idea I have is:

• Get a KVM that supports USB 3.0 connections from two computers (I expect this is USB-B ports) and mini-displayport from two computers, with mini-displayport out and USB-A ports to connect to devices.
• Buy a four port USB-C hub
• use the two macbook ports: one to power, one to the USB-C hub
• Buy a USB-C to mini-displayport adapter and use that to connect the USB-C hub to the KVM's displayport input
• Buy a USB-C->USB-B cable to connect the USB-C hub to the KVM to support the keyboard & mouse
• Buy a straight mini-displayport cable and connect that from Mini to the KVM, and an additional USB-A->USB-B cable to get USB from the Mini to the KVM.
• Plug keyboard, mouse, and monitor (via mini-displayport-to-DVI adapter) into KVM.

Nothing can possibly go wrong with this plan.

OK, seriously, is that the best I can do? Would that even work? Or is there a better way to do this? I would love to get this down to the bare minimum number of things, and would pay a little more to get a KVM that can support my shenanigans.

Bonus points for audio support... currently there are speakers plugged in via the 1/8" jack of the mini; I suspect I'd just have have an additional cable go to the macbook air's audio out jack... unless there's a KVM that doubles as a USB audio sink and can output analog audio via a 1/8th" cable? That would be sweet!

posted by rouftop to Computers & Internet (10 answers total)

If this were my task, I'd keep the KVM simple and cheap and get a decent usb c hub to give you a variety of ports that you could also bring with you when you needed those extra ports on the road. There's a ton of choices there and you might choose a cable that can skip any video adapters. I guess technically, they are cables with adapters built in...
posted by advicepig at 9:49 AM on August 30, 2019

Your plan will not work, unless the hub you buy is actually a Thunderbolt docking station that knows how to negotiate Thunderbolt Alternate mode.

You can’t tunnel from USB -> Displayport via an ordinary USB hub: USB-C to Displayport (or HDMI) cables are actually active cables that negotiate with the USB-C chip on your PC / laptop to put the socket in "Alternate mode" after which it acts as a direct Displayport or HDMI connection. (Possibly just the former & the HDMI cables then convert Displayport to HDMI after the fact, I forget which).

At least one (possibly both?) of the USB-C ports on the Air will be a Thunderbolt port which supports Alternate mode.

What you need is one of the Thunderbolt USB-C hub things that offers both a Displayport socket (or HDMI) /and/ USB sockets. If you plug that into your laptop it should give you the sockets you need. There seem to be various options on Amazon: this thing for instance (not an endorsement - I’ve not tried any of them). Or find an unpowered one & keep powering your laptop with the existing charger.
posted by pharm at 10:14 AM on August 30, 2019

NB. Another options is to put the cash towards a monitor that actually has multiple inputs, plug both devices into that monitor. Then plug your mouse and keyboard into the monitor & use a super cheap USB switch to switch the monitor usb output between your two devices. This is my solution to this problem & it works just fine.
posted by pharm at 10:17 AM on August 30, 2019 [1 favorite]

Actually, for the love of all that’s holy, don’t buy that one, the Amazon reviews look super-suspicious. But something /like/ that Thunderbolt hub.
posted by pharm at 10:25 AM on August 30, 2019

Here's what I'd buy if I were you:

• USB/HDMI KVM - this is way more KVM than you need, but it's also insanely cheap and you're not going to find a good one for less; I own this and it is great, and it leaves you room to upgrade to a much nicer monitor in the future - plug your keyboard and monitor into this
• DVI to HDMI cable - use this to connect the KVM to your monitor. DVI-D and HDMI video signals are electrically compatible, they're just different connectors, so you can use DVI-D and HDMI equipment together with cheap dumb adapters

To connect the Macbook Air to the KVM, you could use:

• USB-C to HDMI adapter - plug one end of this into your Macbook Air and the other end into the KVM
• USB-C to USB 3.1 adapter - use this along with one of the cables included with the KVM to make a USB connection to the MacBook Air

--OR--

• All-in-one USB mini "dock" thing - connect the USB and HDMI from the KVM to this and plug it into the MacBook air - there seem to be much cheaper versions of this that you may be able to get by with, but this is the one I use that I know works

To connect the Mac Mini to the KVM:

• DVI (female) to HDMI cable - use this to convert your existing DVI adapter into an HDMI adapter
• USB cable included with KVM

posted by jordemort at 10:33 AM on August 30, 2019

Oh and re: audio, if you switched out your monitor for a real HDMI one that had built-in speakers or an audio output, you could use that (you'd probably have switch out the adapter you're using with the mini for a real DisplayPort to HDMI adapter instead of cobbling one together with a converter and that actually might not be a bad idea anyway...) or you could get a USB sound adapter and plug it into the extra USB port on the KVM, but you might have to re-select your audio output every time you switch ports on the KVM then.
posted by jordemort at 10:38 AM on August 30, 2019

May I suggest Synergy, the software KVM? I've only ever used it on Windows, but I've used it across up to 3 machines before and it's terrific. It supports OSX.

Essentially it uses network communication between the two machines to share a mouse pointer. You do some basic setup to tell Synergy which edge of your monitor will 'teleport' your pointer to which edge of your second machine's monitor. When your mouse pointer crosses that edge, the focus of your mouse and keyboard is shifted to the other computer. Once set up, it's every bit as easy as using a 2-monitor setup, except that each monitor displays outputs from different computers.

At $30, it's one of your cheapest options for KVM.
posted by Sunburnt at 12:28 PM on August 30, 2019

jordemort: That setup wont work - the Macbook Air only has 2 USB C sockets & one of them has to be used to charge it, so at least one port has to do double duty somehow.
posted by pharm at 1:39 AM on August 31, 2019

Response by poster: Seems like a hub like this would let my mac receive power AND send video/audio (if I get an HDMI monitor with integrated speakers and two inputs as suggested by pharm) AND handle traditional USB devices with a single cord.
So maybe that hub, plus a new monitor, plus a simple USB switch for keyboard/mouse, plus a bunch of USB and HDMI cables... /thinking-face

Oh and a correction, I'm using the HDMI out on the mini, not mini-displayport.
posted by rouftop at 11:13 AM on August 31, 2019

Response by poster: I think this combination might work!

• Convert USB-C to HDMI and USB 3.0: https://www.amazon.com/dp/B07H8N845Q
• Provide power to the laptop via the "PD" port on above: https://www.amazon.com/dp/B07TWCMYL1
• Switch Keyboard, Mouse, Monitor (and it even has a 1/8th" audio out jack!): https://www.amazon.com/dp/B078LY741V
• One 1/8th" double-sided cable for audio

Total cost is about $125.

If there's a cheaper KVM that does what the one above can do (I don't need 4K, but I do want HDMI!) then that would be awesome. Otherwise I think this does it, thanks for you help!
posted by rouftop at 11:47 AM on August 31, 2019