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Building Your Own KVM Switch...With Audio Connectors?
Michael B asks: "I recently bought an 8 port KVM to switch between various workstations and servers at home, and I'm realizing what I can't switch is audio! I've seen 4 port audio/video type switches (for things like switching between video console systems) but this doesn't address more than 4 ports and having the adding RCA/S-Video is a waste. I've thought of building one from scratch using Radio Shack parts, but can't find any info, such as a schematic, online. Does anyone have any ideas or sources of info for this one? Belkin seems to make a 4 port KVM with audio, which would be nice, but I need more than 4 ports. Thanks for any help!" After a bit of digging, I found this monster, which does 8-port KVM and audio, but that weighs in at a hefty $500USD, which is rather expensive. Has anyone managed to find schematics to such switchers so that folks, who aren't afraid of soldering irons, can build their own?
instead of spending $500 or spending all your time building your own switch, just buy a tuner with multiple inputs. you get to have your switch (at the cost of having to push one more button, although if you use the remote it shouldn't be all that strenuous) and you could hook up some advanced (dolby, dts, whatever) audio to it if you'd like.
unless you don't need more than 640x480 video with lots of ghosting, don't build your own. (besides, won't you need a DVI KVM switch soon after your crt dies?).
make your own separate audio only switch.
buy a manual select printer switch and put in audio jacks. vwala. how tough could that be? not being an electronical switch though i imagine you could get some nasty "pops" when changing between devices.
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How about just building an audio mixer? IIRC, Forrest Mims's "Engineers Notebook" (the one on op-amps, I think) has a multi-channel mixer that allows for an arbitrary number of inputs. This way, your MP3s don't stop when you go to work on your laptop, etc.
Take Switch #1 - Plug in 4 computers. Take Switch #2, plug in 3 computers and the output from switch#1. Now you have a 7 Computer Switch with all the features of your 4 port switch, at twice the cost of course.
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Each of the relays would gate the respective sound signals onto a common bus. Use a double pole relay for stereo. 2N2222 (npn) and 2N2907 (pnp) are available from Fairchild through Digikey in TO-92 packages and would be a good choice for a relay driver.
Likewise, an Omron TX2-5V is a reasonably priced DPDT telecom relay with a 5v coil, also available from Digikey.
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If you're just trying to get sound (alerts, alarms , whatnot...) why not just buy some cheap speakers? You can pick up something that'll put out sound for under $10 per set.
If you're looking for higher end sound (music, et all) then you're probably better off dropping the $5C.
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Maybe if you used a USB audio output device and a USB KVM?
I haven't tried this myself, but it seems like it should work.
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Another option might be just getting a 16 point patch bay... You could either do it with 1/4" mono or stereo jacks and you'd only need one or two patch cables.
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Keyboard, Video, Mouse. are you surprised that there is no audio?
get a mixer. there is probably little reason you'd want to play music on more than one computer at a time, so just get a mixer and put them all into the mixer and out the speakers right in front of you.
Buy a cheap audio mixer and control all your sound inputs individually.
Skip the KVM switch. If you have 8 machines at home (assuming you aren't running a business from your home), just start consolodating machines. In the end, you'll probably save on your energy bill.
They sell A/B audio switchers and A/B/C/D audio switchers... use the A/B to select which one of the two ABCD switch to use, then select one of those. Total cost: about 70 dollars max. I think they come in RCA only, so YMMV. Good luck.
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I built a 2X2 for switching two computers to either earphones or speakers. Two DPDT switches, one controls input, one controls output. i1 i1 i2 i2 1 2 1 2 o1 o1 o2 o2 1 and 2 are connected together, i and o are inputs and outputs, left and right. Tie all grounds together, switch L+R. I guess doing that could cause a ground loop hum, but it hasn't caused a problem for me. There isn't really a pop or anything when you switch mine, even with the speakers on. You need reasonably good quality switches though, if the switch feels loose or wiggly, it will probably cause a lot of static when you switch it. I found a lot of my surplus switches were not up to audio use. I eventually settled on push-on push-off switches I scavenged from an old set of speakers, they were power and bass boost switches. This concept is the same way one would build a switch with many more inputs or outputs, you just need rotary switches, DP#T where # is the number of things to switch. Here are some switches The 2 pole 5 position and 2 pole 6 position from there is probably what you want. You can cascade a DPDT and two 5 position rotary switches for 10 outputs with one input or vice versa. Scavaging from manual computer switch boxes is probably not a good idea, since most of those are low numbers of positions, with high number of poles.
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I built a 2X2 for switching two computers to either earphones or speakers.
Two DPDT switches, one controls input, one controls output.
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1 and 2 are connected together, i and o are inputs and outputs, left and right. Tie all grounds together, switch L+R. I guess doing that could cause a ground loop hum, but it hasn't caused a problem for me. There isn't really a pop or anything when you switch mine, even with the speakers on. You need reasonably good quality switches though, if the switch feels loose or wiggly, it will probably cause a lot of static when you switch it. I found a lot of my surplus switches were not up to audio use. I eventually settled on push-on push-off switches I scavenged from an old set of speakers, they were power and bass boost switches.
This concept is the same way one would build a switch with many more inputs or outputs, you just need rotary switches, DP#T where # is the number of things to switch.
Here are some switches
The 2 pole 5 position and 2 pole 6 position from there is probably what you want. You can cascade a DPDT and two 5 position rotary switches for 10 outputs with one input or vice versa. Scavaging from manual computer switch boxes is probably not a good idea, since most of those are low numbers of positions, with high number of poles.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
You don't want to change the audio every time you switch to a new computer. It interrupts the program.
I've seen several recomendations for just using standard audio gear to mix the inputs (and was looking for something like that lastnight). Any recomendations for a nice low end mixer with 4-8 inputs and 2+ outputs, bonuses for rack mountable.
This is pretty trivial to build; you shouldn't need schematics. Audio signals are pure analog, so all you really need to do is get a switch with multiple throws (3 for stereo) and wire it up to jacks and mount it in some kind of box. If you get a rotary switch you could have a pretty much arbitrary number of computers hooked up to it.
If you care about sound quality or having the device look nice, just get a desktop mixer. That's perfect for having multiple computers driving a single stereo.
As to building your own ... a bunch of analog multiplexers (or relays if you want it to be fancy), flipflops, pushbuttons and LEDs, and you should be done. Well OK, it might also be a good idea to use a microcontroller and program it to switch the signals in the proper sequence. Something like an AT89C2051 and a bunch of 'HC164s to control the multiplexers. You could then also add a serial port for configuration.
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It's because she's a girl. Girls just don't understand technology.
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buy a belkin soho .. they are cheap and they support audio and usb.
_
b
Buy 2 KVMs and use one for the keyboard-video-monitor. Open up the second one and buy some panel mount 1/8" audio jacks or whatever will match your cables. Cut off the mini-DIN and DB-15 jacks, LABEL THE WIRES, then solder in the new jacks.
It's because she's a girl. Girls just don't understand technology.
No, it's because they're a retail outlet and most of their business is appliances. They employ people based on retail experience only and it's a lucky coincidence if any of their staff can even recognise a capacitor.
455fe10422ca29c4933f95052b792ab2
Why do you want to switch? Why not put the audio into an analog mixer and have all of them active simultaneously?
For anyone who is actually considering Radio Shack as anything other than an emergency refuge for "awk, I ran out of solder and I need to finish this!"... Radio Shack does not even sell electronics stuff around here anymore. Maybe a bit of soldering equipment, and some connectors, but for actual electronics? Nah. They are morphing into a half-assed Electronics Boutique but with more annoying salespeople. I am fairly certain from other people's stories that this is a trend that is continuing everywhere in the Radio Shack chain.
You're better off finding a real electronics store, or going mail-order. DigiKey is a decent mail-order place for USA/Canada/UK. You will find their selection very refreshing.
Random and weird software I've written.
try google CCTV.
seporate audio switch, who knows
just an idea
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What you are trying to switch is the red, green and blue video signals, which are analogue and have several MHz bandwidth; the horizontal and vertical scan timing signals, which are lowish-speed digital (a few kHz and a few Hz respectively); the keyboard and mouse clock and data, which are low-speed digital (c.1200 baud) but two-way; and the left and right hand audio, which are analogue without much bandwidth (20kHz tops).
:-)
Just how much bandwidth is in a video signal? Well, if you have a screen of 1024x768 and it refreshes at 70Hz, that means the electron beam has to draw 1024*768*70 = 55050240 dots a second, each dot being either a crest or a trough leaving a frequency of 27.525120 MHz in the worst case, when rendering alternate dim and bright pixels. Bear in mind also that the device has to work into a low impedance of 75 ohms, so the on resistance - and the switching time - are as critical as the propagation delay.
The bidirectional digital signals are not a problem. Analogue switches will handle them. Think: switch off = different voltages both sides, switch on = same voltage both sides.
You will need some really high bandwidth analogue switches for the video, but you'll get away with 4066-type for the audio and data and maybe the timing. Take a look at http://www.maxim-ic.com for parts and schematics. The basic principle, though, is to connect all the switch ICs to switch one device at a time onto a set of common rails for R, G, B, HS, VS, KC, KD, MC, MD, LA, RA.
Another option would be to mod an existing unit with some 4066-type analogue switches. You'll need a +-5V supply from somewhere. Drive the switch gates from the switching signals in the first unit. A really impressive feat if you can manage it would be to construct a simple audio mixer (use a 2904 op amp) and rig it so the unselected channels are still fed into the mix, but at a lower volume. Then you can still hear death screams
Don't even *think* about using any kind of mechanical switch or relay. Moving parts suck bigtime and will distort any analogue signal you try to pass through them.
jameco is pretty good, too. Their selection is much smaller than DigiKey's but it's oriented slightly more towards the hobbyist. They both have good online and free paper catalogs.
1600 x 1200 resolution at 75 Hertz refresh rate is: 1600*1200*75 = 144 MegaHertz. The video system bandwidth must be much greater than that to avoid ruining the video quality. That's why even the $30 nVidia video adapters have a 300 MegaHertz RAMDAC (digital to analog converter).
19 inch CRT monitors with a 1600 x 1200 resolution cost as little as $225, so that resolution is becoming a standard.
It is a big technical achievement to switch 1600 x 1200 resolution without video degradation. IO Gear does it by having special video processing amplifiers inside the KVM switch. Building a KVM switch is not something most people would want to attempt, because it would cost so much in time.
As was mentioned above, #5923272, a tuner is a good cheap solution. They can be had at garage sales for considerably less than $50 sometimes. Mostly you don't want to switch the audio when you switch computers. It interrupts whatever you are listening. For example, presumably you want only one computer signaling if you have email.
IO Gear is a little bit flaky at times. Notice that their GCS1714 KVM switch is listed with a "case weight" of 27.25 pounds, but the weight of an entire package is listed as 4.7 pounds. Presumably they mean the weight of a case of KVM switches, but the quantity is not specified.
Note that IO Gear (at least sometimes) plays games with the supplied cables. A four port KVM will be supplied with 2 ten foot cables and 2 six foot cables. The shorter ones are too short to use in some installations. That isn't mentioned on their web site, that I can see, or in the manual, available online.
Also, the keyboard controls for switching may not be well considered.
IO Gear does seem to be the best for video quality.
You could daisy-chain the soundcards - i.e., the LINE-OUT from one to the LINE IN of the next one. The last PC will have its speakers playing all signals mixed and the cost will be very low (just stereo cables).
But how much technology does a girl need to understand? All we really need is a good, sharp knife. (Or, worst-case scenario, a carefully-wielded student ID card.)
This guy is a jack of all trades, master of none. Take his advice with a wary eye as he is a know nothing person who seems to have something baseless to say about everything. If anything, his convict uncle works for Jameco and he is getting a penance for doing this.
...from an architecture so lame it never originally featured audio...so why bother switching it? These things are designed for PC's, Sparcs and Macs et al. always have used custom keyboards / vid connectors...
this could be forgiven by the simple fact that you're average home user isn't going to need one, and no-one listens to music @ work do they (or at least the boss doesn't think so *grin*)
I found this at newegg.com
It's 2 ports, supports audio & is only about 90$.
"...we dont care about the economics; we just want to be able to hack great stuff."
How about that:
/dev/audio | nc 192.168.100.1 48050
/dev/audio
Machine you work on:
cat
Machine you plug your speakers in:
nc -l -p 48050 >
I mean, you said you have a mix of servers and workstations at home. Do you really need to hear the Windows bell or chime sounds on your servers (or if you're running linux servers...why do you have them configured to make sounds?)?
It just doesn't seem worth the effort to try to find a solution to this "problem" when it doesn't even seem to be much of a problem. But you're certainly free to spend your free time doing whatever you want, including trying to hack together your own KVM switch.
Good luck.
PC Speakers are reasonably inexpensive. Just get a second set for the second comp for $9.97 at Radio Shack.
http://www.practicallynetworked.com/review.asp?pid =468
To summarize:
You can build mixers pretty easily using op-amps, and Forrest Mims' "Engineer's Notebook" has quite a few useful designs.
Where to get it? Rat Shack, although these days it's often not stocked (just like their 150-2160 UHF-only TV antennna grumble grumble)... RS is going downhill.
RS is definately not the optimum place to get electronic components, but when you need something fast and you aren't buying that much, it's quick. Digi-Key is far better, but keep in mind that DK sucks for small orders. ($5 surcharge for orders under $25, in addition to the $5+ shipping costs.)
You should be able to find some mixer designs on the 'net as well. www.headwize.com has lots of audio designs, although most of these are amplifiers and I'm not sure if they have any mixers.
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3x female 1/8" stereo jacks
4x female RCA mono jacks
4x SP/DT slide switches (3/16" x 1/2")
2' jumper wire
1x plastic electrical junction box
1x clear plastic picture cover from picture frame. (3"X5")
First 4 parts are available from RadioShack for a total less than $10. The junction box is available at Lowe's for $1.66. The picture cover you can get with any cheap picture frame.
step 1: lay the junction box upside down on a piece of paper and trace. Cut out the outline.
step 2: lay out the jacks and switches on the paper. the 4 jacks go with the 4 outputs (or inputs as you see fit) and the odd jack out is your static out/in.
step 3: glue the paper to the plastic
step 4: drill and dremel the plastic according to the paper pattern.
step 5: screw/glue all audio parts in.
step 6: flip over and solder all left channel and right channel negatives together.
step 6: solder wires from your static jack right channel to the middle-left side of each switch and the left channel to the top left of each switch.
step 7: solder the middle right of each switch to the CORRESPONDING input/output jack's right channel and the top right to the jacks left channel.
step 8: place the plastic on the junction box and seal with glue or screws
... When a switch is in the on position, that jack will get signal. When it is off, it won't.
To use as a multi-out: place the output from your computer into the static jack. Run lines from the other jacks to your computer speakers, stereo, tv, headphones
To use as a multi input, connect your speakers to the static jack. Connect all inputs to the other 4 jacks. When the switch for a jack is on, it's signal will goto the speakers. When it is off, it wont.
I built this cause I was sick of switching my sound cables everytime I wanted to switch from my computer speakers (when playing games) to my TV (when watching DVDs on my DVD out) to my headphones (when listening to music while coding and my roommate was sleeping).
CAUTION: this is a PASSIVE system. IF you are using it as a multi-out, there isn't much danger. You will just get decreased volume as you turn on more outputs because the signal will be split. If you are using it as a multi-INPUT system and try to input several signals to the speakers at once, you can run the risk of blowing them.
If you have any questions, reply. I'll give you my ICQ and write up some clearer diagrams.
-Ab
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Of your three (non-sig) sentences, "A tuner is a nice idea." Seems closest to error free. It does beg the question though, "Is a tuner really an idea?" It seems more like an object to me. Would it more accurately capture your meaning to say, "To solve this problem with a tuner would be a nice idea?"
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I actually just daisy chain the inputs of my PCs. Take the line out of one. Plug it into the line in of the next. Rinse. Repeat. The only drawback is trying to keep track of two channels (in and out) on each software mixer instead of just the line outs. The advantage is that the final PC in the chain acts as a master volume.
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I have a set up were I like to watch movies on one machine, have my mp3 database on another, and e-mail on another. Yes i do like to here my mail application make a faint beep so I know i have new mail. So i used a 5 channel mixer, obviously for your purposes an 8 channel would be a better solution. One of these can be easily found at a pawn shop for less than 100$. But to be elegent one day I plan to convert my KVM to having 1/8" heaphone jacks for each machine and wire them altogether to one master. That would include only drilling holes in the back and srewing in the jacks. the soldering to connect them all is very light duty soldering. This system would of course not switch the sound from machine to machine but pass it thru from all machines. But it is on the super cheap and relativly easy. Provided you have room in your KVM.