Now that I have finished my DIY Projector, I am enjoying playing video games and watching HDTV and movies on my large screen. The only part I am not enjoying is the swapping of which component is connected to my projector. I have my CenterStage CS-1 that I have my Nintendo Wii and DVD player attached to, and I have my computer that has my HDTV card inside. So, I am constantly crawling under my desk to connect/disconnect the projector from my computer and then routing it to/from the CenterStage. The solution? Get a DVI switch box. So far, I have only found fairly expensive DVI switches, and they don't quite do what I want. My ultimate goal would be to never have to plug/unplug any component in my whole connection scheme.

So, after doing quite a bit of research, I found out that the dual link digital DVI connectors only use 24 pins (out of a possible 29 pins on the connector). Further research unveiled a DB25 Cross-Over switch for printers. My thought was that since the printer switch is a 25 conductor switch, it has enough contacts to switch a DVI connector. Plus, the Cross-Over switch actually has 2 separate connection paths through it, instead of the typical 3-to-1 or 4-to-1 printer switches. I am going to attempt to replace the DB25 pin connectors of the Cross-Over switch with solderable DVI-D pin connectors for a DIY dual-link DVI-D Cross-Over switch.

Some pictures to better illustrate my idea:

1) Here is the DB25 Printer Cross-Over switch.
Click to view attachment
The idea is that the unit has 4 connectors (A, a, B, b ) and a 2-position switch. In the first position, AaBb, connector "A" is routed to connector "a", and at the same time, connector "B" is connected to connector "b." In the second position, AbBa, connector "A" is routed to connector "b", and at the same time, connector "B" is connected to connector "a."

2) Here is how I plan to connect my components.
Click to view attachment
In the first switch position, AaBb, I will be able to use my computer with my normal desktop LCD monitor and I can either play the Nintendo Wii or watch a DVD on my projector. In the second switch position, AbBa, I will be able to use my computer to watch HDTV, or play a PC game, on my projector; I probaly won't use my desktop LCD monitor for playing the Wii or watching DVDs, even though they will be connected in this position.

Here are some quick shots of the solderable DVI-D connectors I bought.
Here is a shot from the front. Sorry about the glare from the flash.
Click to view attachment
You may or may not be able to tell, but the second row of pins on the back has a longer lead to solder to. That will be quite helpful.
Click to view attachment

Finally, here is the inside of the AaBb switch. I will have to work my way through this spaghetti, but it shouldn't be too bad.
Click to view attachment

I probably won't get a chance to work on this until the weekend, but I hope to be able to test it by next week!

Wow, That will be really sweet when you get that working.

Good luck!

Do you think that switch has enough connections??

I have a VGA version of that switch, and they are terrible. Any resolution above 640x480 will give you ghosting issues.

Wow, I hope not! I am running my projector at 1280x1024, so I should definately notice ghosting if I fall victim to it.

Well, the parts were pretty inexpensive, so I think I will go ahead and try it anyway. I will post my results either way.

Well, I had some time today to work on this switch. The first thing I noticed is that the DVI connector is smaller than a DB-25/parallel port connector. This makes the mount in the switch box too big for the new DVI connector. So, I built a mount/adaptor that allowed me to mount the DVI-D connectors to the switch box housing:
Click to view attachment
Then I decided to replace both the 'A' and 'a' connectors and test it out. Here is what the new DVI connectors look like mounted in the switch box:
Click to view attachment
Then a quick zoom out to see the entire back of the switch box:
Click to view attachment

The result?... It did not work. I put this switch in between my computer and LCD monitor. When I unplugged the monitor from my computer, I got the default WinXP sound when you unplug any hot-swap device (monitor, USB device, etc). Then, when I connected the LCD through the switch to the computer, I got the default WinXP sound when you plug in any hot-swap device. That's good. Unfortunately, the monitor would not display anything. That's bad.

I used a DMM and continuity tested all 24 pins between both connectors, and all are in contact. I then tested adjacent pins on each connector to see if maybe I accidentally shorted any pins. Everything checked out clean.

If anyone has any suggestions on getting this to work, I would appreciate it. I was hoping that I'd have a bit different luck than Chad N. seeing as it was a digital connection vs. his analog connection. Ghosting in analog signals makes sense, but not in digital signals. Too bad I got no picture.

Oh, I guess on last thing to mention is that each connector housing is connected. Thus, the outside 'D' shape surrounding the pins of port 'A' is electrically connected to the outside 'D' shape surrounding the pins of port 'a.' I thought this wouldn't matter, as the parallel ports that were there had a wire soldering all of their housings together. Is that a good thing for parallel ports but a no-no for DVI connectors?

OK, I don't know if I am talking to myself on this one or not , but I did find one other piece of information that may help you help me. When I use my newly wired switch inbetween my computer and lcd, the lcd is actually in standby mode.

If I unplug the LCD from the switch, the lcd pops up a message saying 'no signal detected.' When I plug it into the switch, the power button changes from green to orange (thus indicating standby mode). The 'no signal detected' message disappears from the screen. I tried moving my mouse just to make sure the PC didn't place the LCD into actual standby mode, but no luck.

So, I am at the point where the CPU recognizes that the monitor is plugged in because the hot-swap sound for attaching the monitor is heard. The LCD recognizes that it is connected to the computer because it is in standby mode and no longer states 'no signal detected.'

Does anyone know what the specifications are for a monitor's standby mode? Is there a voltage level reading on certain pins that forces the monitor into standby mode if it drops below a predefined value? Does anyone know that value? Does anyone know what pin numbers they are on a DVI connector? I found out that Pin 14 on the DVI connector is '+5V Power for Standby Mode,' but I don't really know what that means.

I am not trying to beat a dead horse here, but after seeing this auction on eBay, it seems to me that a passive DVI switch is possible.

well im sorry i cant help but i just wanna jump in and say that's an awesome build, i would need something like that lol

oh and btw im allso using 1280x1024, is it sweet?

Thanks for at least chiming in. I have been doing some research on this topic, and I think that this idea won't ever work without some type of signal boosting. The DVI specification says that the DVI signal transmitters have to be able to transmit the data up to 5 meters. Any further distance will require a signal repeater/booster. Since I am using a 6' DVI cable from my PC to my switch, and then a 6' DVI cable from the switch to the monitor, I am assuming that the 2 DVI ports, all the internal wiring, and the internal switch are degrading the signal to a point where it is too weak to work properly. Also, I am using a 15' DVI cable for my projector, which is at the upper limit of the specification.

I have been looking into DVI repeaters, and there are some models that say they can drive the signal up to 50+ feet away! Unfortunately, they are all $150 or more. Since I would need 2 of them, it is way too much money to spend just to save me the aggravation of unplugging and plugging in different cables (and too much money to prove my signal degradation theory). If I can find someone locally that has a DVI repeater so that I could test my theory, that would be great! Until then, I think this project is on hold.

By the way, in my research for DVI repeaters/splitters, I came across some DVI Matrixes that would accomplish exactly what I want to do with this switch, but the smallest ones (a 4x4 connection) are at least $800.

As to the 1280x1024 resolution, it is awesome. I use that resolution mostly for 720p HDTV. I do use my CenterStage CS-1 to upscale DVDs and my video games to this resolution, but anything upscaled will show some pixelation. Plus, anything running full screen will show my focus problems with my keystoning. So, overall, I am definately glad that I went for the higher resolution, but in reality, only HDTV uses that resolution well. (If you don't do any keystoning, or if you can achieve it with lens shifting, I think you would be extatic about how nice full screen computer games look on it).

A DVI connector has two relevent types of signals for your application: a relatively slow set of control wires and a very fast set of video data wires. Basically the result you are seeing means that the switch is working well for the low speed control signals, such as power management etc, but not working for the highspeed signals. I can think of a number of possible reasons that the high speed signals might not be working.

1) Length mismatch

The highspeed video signals are sent on pairs of wires using a method called differential signalling. If the length of the two wires in the pair are not very very closely matched in length the link will not work. This unfortunately includes any length mismatch within the switch mechanism itself.

2) Cross talk

A parallel port operates at maybe 10MHz where as a DVI port might be as high as 200MHz. At low speeds that rat's nest of wires works fine but at highspeeds they cause all sorts of noise to couple between the different wires. Luckily you might be able to deal with this problem using careful wiring techniques. In particular each pair of differential signals need to be kept very close to each other the entire time. Perhaps if you create a length matched twisted pair of wires for each set of signals you will have better luck.

3) Impedance mismatch

The last possible problem might be noise caused by an impedance mismatch. Wires and switches all have an electrical characteristic called impedance. Perhaps you have heard of 75 ohm coxial cable. This type of cable is designed to have an impedance of 75 ohm. All wires have an impedance and if you start mixing different impedances together in a high frequency communication channel you will get very poor signal quality. Basically what I'm saying is that DVI expects 50 ohm impedance where as your rats nest of wires is unlikely to be 50 ohms. Additionally even if your wires happened to have 50 ohm impedance who knows what the mechanical switch itself has inside. Unfortunately I don't have any good suggestions for avoiding this problem.

Good luck.

I am not sure but this might work
http://www.geeks.com/details.asp?invtid=2P...TCH&cat=MON

this between your PC and Box and using a hdmi to dvi-d connector to your PJ may work. But I have not tried this but it sounds like what you are trying to do. ,,,,Good luck Joe



You will more than likely have to place this on your TV out side of your graphics card

Thanks for the input. I have a feeling that it is mostly an impedance mismatch issue with at least the switch, if not also the wire. I looked into some tri-state bus circuitry to use instead of the mechanical switch, but they are not offered in a nice DIP chip; they are mostly offerred in surface mount packages which I have a hard time soldering to. I guess I will have to abandon this project

Yeah, I have looked into that. I am surprised at how cheap HDMI swtiches/repeaters are, but how expensive DVI switches/repeaters are. Since you can buy HDMI-to-DVI adapters, they can't be all that different. Too bad I am using DVI with my LCD. Since I am probably going to have to go commercial with my switch, I will keep the HDMI solutions in mind.

As far as I know the only difference is HDCP (which you obviously aren't using), so I say get some cheap hdmi to DVI cables and use HDMI switch boxes.

I am pretty sure that it is the exact same signals, just different connectors (IE, all the adaptors I have ever seen are just passive, passing the data to the proper pins).

These are $18 apiece for the cheapest:
http://www.monoprice.com/products/subdepar...0110&style=

Just use some of these cables for the hookup 10' for $6.42 on the cheap ones (hint, use 3-foot for the box next to the PC):
http://www.monoprice.com/products/subdepar...0231&style=

I hope you get it worked out, cabling is not an issue for me, but a quick question, I am trying to build a 720p projector, how did you do it? I can't make any of my LCD's display proper 720p from my Samsung TV Tuner or my VGA modded Xbox, they alway scale and stretch the image (even 4:3 winds up at 5:4 )

I am almost ready to buy the 17" widescreen 720p native (IE 1280x720 pixels, none of this 13XX by 768 crap) from Gateway, the upside is real 720p and HDCP, and a 4:3 aspect mode, the downside is it is larger than a normal 17" (I might be able to fit it in a wide 15" stock box though) and it costs $200 new.

Actually, HDCP is 'available' across a DVI connection also. It's just a content protection scheme, and can be imposed on digital signals across both connector types.

HDMI on the other hand also carries Digital Audio across the cable, so you can have video and audio all in one connection.

The adapters just don't connect the audio pins from the HDMI side to the DVI side, as there is no where on the DVI side to connect them to, since they were not part of the DVI specification.

My LCD automatically stretches any input signal to fill the entire screen, just like yours. However, I am only ever sending it a 1280x1024 signal, so I don't have to worry about it...

- I have my computer set to output 1280x1024, so when I watch HD TV through my PC's TV card, the software adds the top and bottom "black bars" to the image when I switch to 'full screen.' Since the software is adding the black bars, the actual size of the image sent to the projector is 1280x1024 and the LCD doesn't have to scale/stretch anything; thus it maintains the proper aspect ratio.

- I have my Nintendo Wii and DVD player hookup up through a CenterStage CS-1 video processor. I have the output of the CS-1 set to 1280x1024, so it scales all the input signals proportionately and adds black bars on the sides for 4:3 and to the top and bottom for 16:9. Again, since the output is set to 1280x1024, there is no need for my LCD to scale/stretch the signal.

Basically, since my LCD can't maintain the input aspect ratio, I took my LCD out of the equation. Now, my setup means that everything has to go through my CS-1 or computer to look correct, so I would have to pump any X-Box through the CS-1 instead of directly into the projector or I would run into the same issues you are having.

Ah, I am guessing that the CS-1 is not a cheap option, the only recourse I have is a Gefen, it is pretty affordable at $270 ( http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...em=150099438935 ), but at that price it is more expensive than my box, optics, and light engine, and I am trying to use an LCD under $100:

It almost is enough to force me into the Gateway 720p HDCP monitor for $200. I may get my box big enough for it and use a 15 or 17" monitor while I decide. Then later I can get one. $200 is pretty cheap for real 720p w/HDCP. I am planning on ordering a Tescorp box, and an extra-wide 15" box would probably be more expensive. But if I don't buy the panel now I could probably afford it. Ebay has one for $185 (S&H included) and the eMachines version (VGA only) is $160 (S&H included), I am leaning more and more toward it.

Any news on the DVI Dual-Link front? For $60 you could probably have the cabling/adaptors and switch boxes from monoprice.

The problem with your DIY box is probably that spaghetti mess of cables in the box, maybe get some mini-Coax pairs (or open a DVI cable and use those wires). If you properly shield the wiring to the switch, then the only problem will be the actual switch, and I don't think it is that bad. The bonus is that the pairs will make it easier to see where the wiring is going. The insane digital uncompressed bandwidth of DVI is really not conducive to transmission. Is VGA noticeably worse in quality? I tried both and VGA looks just about the same to me on my LCD panels.

Yeah, it retails for an arm and a leg. I got lucky to grab mine off of eBay for around $250. You just have to keep your eye out for a while. I just checked now, but I only found one, and they want almost $450 for it!!!


I got ahold of a DVI KVM switch to try out. The switch is older, so the outputs are not amplified. I found that the switch worked beautifully for my computer, but when I hooked up the CenterStage CS-1, the signal would blink out and then back in just about every second. I have no idea why, but it was quite annoying and definately not watchable. So, I am hesitant to spend any money on this when I don't think it will work. The switches that have amplified outputs are a lot more than $60 with cabling.


I would guess VGA is not worse quality. I don't know, never tried it. I bought a 15 foot DVI cable for the projector and never looked back.

Dude here is a cheap solution for you
one of these

Click to view attachment

I have this and it works for the PC just fine (DVI-D) the only thing to note is that it doesn't work well with a long cable out to the projector, for that you would need to add a booster. The easy fix is get a short cable (3-6ft) from the switch to the pj.
you could also get the 4x1 but the 5x1 is only $9 more and gives you room to expand.


Then you will need some combonation of these cables (5 total 4 in 1 out)
Click to view attachment

3ft - HDMI->DVI

6ft - HDMI->DVI

10ft - HDMI->DVI

They make longer cables but DVI is not so good on long runs without a booster especially when going through a switch. On my setup when the cables were too long the image would come on then lose sync or somthing (go to black) then come on again but not stay on.

Here is a full selection of HDMI -> DVI Cables

You are looking at like < $100USD for the whole setup!!!

Thanks for the info. I will have to look into this a little more. As for a shorter cable to the projector, that is a no go. My projector is mounted to my ceiling, and I need the 15 foot cable to route it out of site and still reach to the entertainment rack. A quality DVI signal booster is still around $100, so I have to give it a little more thought.

I found some cheap extenders on eBay, at first I was skeptical, but then I tracked down the chip one of them claimed to use:

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4444

It claims a 36-meter extension, I just need to find out if they can indeed be cable-powered, IE if the cable has a power pin in it, or if it can be powered off of the signal voltage.

http://search.ebay.com/search/search.dll?s...e=hdmi+extender


Quote:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...em=140131270072


Edit: According to: http://en.wikipedia.org/wiki/HDMI there is a +5v on the pinout of HDMI that can power the in-cable extenders, I think that for $30-40 it may be what you need. 15' is pretty close I needed a 25' VGA cable just to reach my equipment, but I have it under the screen I project onto.

Wow! Thanks for all that research. The 3815 chip looks to support the DVI resolutions that I want. I did some quick research after reading your post and found a similar model of HDMI Extender to the one you found on eBay. It uses the 3815 chip, draws the power from the cable, and is $5 cheaper. Since I will have to order DVI-HDMI adapters for my cables (already have plenty of DVI cables), I might want to get them all from the same place.

Hmm. I will have to talk to my wife about this. You have definitely given me something to think about. Thanks!

Will you need a booster for all the cables? Or just the line to the PJ? If you use 3' and 3' (or 1.5' and 3') to the PC and then just a single Signal booster on the line to the PJ. On the upside if you get 3-4 1.5' DVI-DVI cables it will be cheaper in bulk.

Wow, that is one specific setup you have, I envy you the PJ, all I have right now is a really hot and old Infocus 640x480 that uses Halogens, I need to get on with building my PJ.

Ok, for those of you who actually followed this thread at one point in time...

I have abandoned the DIY aspect of this idea due to the complexity of signal timings, etc. So, the next best thing to DIY is... inexpensive!

I have decided to take some previous posters' advice and go with an HDMI switch solution. I ordered the Joytech HDMI Tri-Link switch:
Click to view attachment
This is a 3:1 swith that draws its power from a USB port or wall wart. Since my computer will be one of the inputs, I will plug the USB cable into that and not use the wall wart. It has a remote control and is supposed to support HDCP.

I decided to continue to use my DVI cables instead of buying new HDMI-to-DVI cables, so I also bought HDMI-to-DVI adapters:
Click to view attachment
Nothing has arrived yet, but hopefully I will have it all by this weekend. So far, I have gotten away with only spending $35. I will probably need an HDMI signal booster, but as others have posted, they are only about $30. I will wait and see how this initial setup works before investing in the signal booster.

Very nice, where did you purchase the stuff at?

I bought the switch from Buy.com for about $27 (I had a 5% off coupon), and I bought the adapters from monoprice.com for about $10.

I still give you credit for having cheap solution to an expensive problem.

Ok, the switch worked! I now have the following setup:
Click to view attachment
My computer is setup to use both video card outputs (DVI & VGA) in the 'clone' mode so that the same desktop is displayed out each port. So, my computer is driving my LCD Monitor constantly, and also driving the input into the HDMI switch. My CenterStage CS-1 is also plugged into the switch, so all I have to do is set the switch to the right input to play Wii games/watch DVDs versus watch HDTV/play PC games.