Removing Video Connector, Solder wires to board?


22 posts
by StevenPi » Tue Dec 11, 2012 6:49 pm
Hi this is my first project and I just got my Raspberry Pi a couple days ago. I need a case for my RasPi so I wanted to do the thing where you put it in and old game-boy. I pretty much have everything I need (the rest of my project should come today (soldering iron, heat shrink tubing, etc.)) but I came across a problem. With the way I want the placement of the Pi to be in the Gameboy (bought off Ebay by the way for $15.50) the composite video connector is too compacted. I want the GPIO pins to be accessible through the battery compartment of the Gameboy for easy access. My screen requires the composite video cable but with it connected, I would have to cut a hole in the side of the gameboy for the connector to stick out a bit. That would look awful.

I was wondering, it looks like the connector on the Pi is an easy thing to desolder.......is it possible to de-solder it and then cut a composite video cable and then solder the wires of the cable directly to the board? And would it matter which wires go where?

If it sounds like I have no idea what I'm doing, I don't. All help is appreciated thanks :)
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by mahjongg » Tue Dec 11, 2012 7:25 pm
Its not that easy to de-solder at all, best option is to use a wire cutter, and cut away the two pins in the back, so that the connector is only mounted to theboard by the middle pin, then heat the remaining (middle) pin to remove the connector. If you do not cut the two pins, you will find it very hard to melt the solder of all three pins at the same time, as the back pins are more or less directly connected to a large copper area (ground plane) of the PCB, and that draws all the heat away. If you get the connector off, you can remove the two pins one by one.
The two back pins are connected to GND, and so must be connected to the coax cables shield, the middle pin is the signal pin, and must be connected to the coax core.
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by StevenPi » Tue Dec 11, 2012 10:29 pm
Sorry I don't really understand :? What is GND and "coax core"? I don't understand any of this and it's so hard to learn it on the internet :cry: People just assume you know the smaller things so for the people who know absolutely nothing (me) it's impossible to understand it all.

Well my soldering iron came.
So if I manage to unsolder it, I just have to connect the cut cable to the middle pin? Since it's the signal pin?


And by the way, where is a good place that I can learn all of this stuff? Where did you learn it?


Thanks :)
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by Burngate » Wed Dec 12, 2012 10:40 am
I personally would disagree with mahjongg regarding the desoldering of the socket.
I would first melt the solder on the middle pin and gently lever the socket up. Then do the same on one back pin, then the third pin, then the front pin again, .... after several times round it should drop out.
Whatever, if you can do it his way then do it.

But a more important piece of advice - before you approach your Pi with your new iron, have a practice with some gash piece of board from something unimportant. Soldering is a skill that requires learning and practice.

If you examine the video socket, you'll see it's got the metal outer connected to the rear two pins, and the middle pin is connected inside the plastic. Looking at a standard plug, you see the same thing, outer metal with inner prong.
If you cut a video cable open you'll see the same construction - a centre wire surrounded by a metal outer screen. The centre wire carries the signal while the outer screen acts as a return path for the signal current (all electrical things work as circular paths - electrons need somewhere to go, they can't just drop out of the end of a wire) By convention, the negative part of a circuit is called ground or earth, because that was where it was connected when Marconi was a lad.

So after you've removed the socket, solder the inner wire of your coaxial cable to the middle / front hole, and the screen to one of the back holes
Wyszkowski's Second Law: Anything can be made to work if you fiddle with it long enough.
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by mahjongg » Wed Dec 12, 2012 11:08 am
Yes, burngate is right, for a patient person, and if it works, this is the best way. Also don't be afraid to add some solder when trying to melt the solder in the pad. It might be counter intuitive to add more solder, but it will help to melt the solder easier.

I myself am not that patient, so I will take a shortcut by cutting away the two pins that I have access to, so I have only one single pin to heat to get the darn thing off.

I use the same technique to remove, for example, a DIP IC from the board, first I cut off all the pins of the IC, then I remove the pins one by one.
Obviously if the IC cannot be discarded I need to melt all 14 or 16, or maybe even 20 pins, but for that special tools do exist.

As for the question where you learn all that, well you learn some basics at school, but the rest in over 30 years of doing it. :lol:
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by StevenPi » Thu Dec 13, 2012 2:19 am
Thanks guys :)

I guess I'll unsolder it then but it'll have to wait until tomorrow to buy a new fuse for my multimeter so I can continue working. It's brand new and I already broke it :oops:

I'll let you guys know how it worked out :D
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by StevenPi » Sat Dec 15, 2012 11:00 pm
Well Okay I decided not to unsolder the connector on the board since there only isn't space for it when I plug something in and if I could keep it intact good. And I can :D

I can just solder the wires to the pins sticking out the bottom :D
One thing to note though: The front single pin is NOT the signal pin. The two back one are with the front single one being ground. I haven't soldered the wires yet but I cut off one end of a composite connector and just touching the wires to the correct pins I get a signal.

I'll post pictures when I finish up the project. There are still other things to do though. :D ;)
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by Burngate » Sun Dec 16, 2012 10:34 am
StevenPi wrote:One thing to note though: The front single pin is NOT the signal pin. The two back one are with the front single one being ground.

He's only right !

I'm Never wrong, not Ever, but this time I'm Wrong :oops:
Wyszkowski's Second Law: Anything can be made to work if you fiddle with it long enough.
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by aTao » Sun Dec 16, 2012 11:18 am
Burngate wrote:
StevenPi wrote:One thing to note though: The front single pin is NOT the signal pin. The two back one are with the front single one being ground.

He's only right !

I'm Never wrong, not Ever, but this time I'm Wrong :oops:

Well, mostly right.... One of the back pins is signal, the one near the board legend "S4", the other back pin and the front pin are GND.

In theory soldering wires to the middle of a video circuit is not a great idea (even if the middle is really right near the plug), it can cause reflections and ghosting on the image.
What I would do I this case is get only the centre pin from a connector and solder the centre wire of the video cable to it, push this into the socket from the back. If possible keep the screen of the cable intact as far as just inside the body of the socket, with a tail that can be soldered to the GND pin of the socket where it touches the board.

As was mentioned earlier soldering is an art that needs practice, there seem to be several soldering tutorials on the net, they are well worth a look and do practice. The Book on just what happens when soldering is about 3 inches thick and covers in detail 9 distinct steps in the process, desoldering is even more tricky. Dont worry though, on the same scale The Book on riding a bike is several volumes.
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by rurwin » Sun Dec 16, 2012 11:26 am
The wire you use to connect to the board need some care and attention. Composite video is a high frequency signal and it is prone to noise and ghosting effects if you get it wrong. For a few inches you can probably use any old coaxial cable that you can find. You could even use individual wires, but in that case you should twist them together. For a wire of any length you should use 75 ohm coaxial cable. Coaxial cable comes in three impedances: undefined for audio frequencies, 50 ohm for CB radio etc, and 75 ohm for TV and video. If you try to use undefined or 50 ohm cable you'll probably get ghosting on the screen.
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by Burngate » Sun Dec 16, 2012 12:05 pm
rurwin wrote:The wire you use to connect to the board need some care and attention. Composite video is a high frequency signal and it is prone to noise and ghosting effects if you get it wrong. For a few inches you can probably use any old coaxial cable that you can find. You could even use individual wires, but in that case you should twist them together. For a wire of any length you should use 75 ohm coaxial cable. Coaxial cable comes in three impedances: undefined for audio frequencies, 50 ohm for CB radio etc, and 75 ohm for TV and video. If you try to use undefined or 50 ohm cable you'll probably get ghosting on the screen.

At the risk of being wrong again, ...
Video - high frequency? Compared to audio perhaps, compared to USB 2? 5MHz cf. 480Mb/s?
And audio, coming from the telegraph era, should be 600Ω but usually isn't; 110Ω is sometimes used for data; 50Ω was the usual HF impedance and was used for Ethernet

Reflections and ghosting ... you'll only get that if the cable is long enough.
With the highest (composite PAL/NTSC) frequencies being around 5MHz, so 200ns period, you'll get some noticable degredation if the reflection arrives >20ns after the original. With the speed of light being 1ft/ns you'll need 10 feet of cable to see something.
Ghosting is usually a delay exceeding about half a us, or 50m of cable

Oh I do like to nit-pick :)
Wyszkowski's Second Law: Anything can be made to work if you fiddle with it long enough.
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by tmpp » Sun Dec 16, 2012 12:29 pm
Burngate,
to pic on you :) -- the dielectric of the cable is a factor and your distance needs to be shortened by the sqrt(er) where er is the dielectric constant of the plastic, ?2.5?
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by rurwin » Sun Dec 16, 2012 1:30 pm
But that only makes a difference of about 20-50%; the argument still stands.

Personally I doubt a few inches of 50-100 ohm cable or a couple of centimetres of connector would make much difference, but I'd defer to anyone with hands-on experience of a composite video signal.

The take-home for StevenPi would be that it's simple and cheap to try stuff out, and opinion is divided as to how rigorous you need to be.
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by Burngate » Sun Dec 16, 2012 3:43 pm
Okay, I'm coming from the OB side, where any pictures are good.
Inside stuff I made, I never bothered with matching the wiring to the nominal 75Ω. More important was cross-talk between signal wires.
Outside the box, matching was rather more important, as you tended not to get a picture from the 5 furlong start down to the finish line unless you did.
Once digital video came along, 270MHz didn't work very well even inside a box, so the 75Ω and proper screening was the way to go.
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by StevenPi » Thu Jan 03, 2013 5:31 am
Sorry it took me so long to post pictures, I haven't worked on my Pi in a while.
Anyhow the screen, powered USB HUB, and Ras Pi itself are all wired up and working now and they are all powered off of the same power source. Here are pictures of my wiring (pics taken with iPhone sorry about quality).

Image

Note the signal wire isn't soldered (though that's EXACTLY how it would be and has been) because for now I didn't want it connected to the pi so I can use the Pi on my computer screen without dragging around everything else.

Image

That's everything connected to the same battery. Note the signal wire for the screen (yellow) isn't connected for the time being.

Image

There's all the wires branching out. The two thick black ones are for the powered USB hub.

Image

That's the connector for the screen. The white and red are for audio that doesnt exist (can't put out sound so they are useless really) (the red IS ALSO THE POWER), the yellow for video signal, and the black for ground. I've cut down the white wire to keep it out of the way.

That's pretty much my completed project. Thanks for your help guys :)
(Would show it working but battery is dead. Sorry :( )
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by dasimpson » Tue Jan 22, 2013 7:29 pm
i would suggest joining this site http://www.retrovia.ie/forum.php they is a few of us who have mooded rpi into gameboys mine included join and have fun also cpmare war stories i have a few of my own lol
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by dasimpson » Tue Jan 22, 2013 8:10 pm
also the very front pin if ground the 2 pins at the back of the conneter or the video out terminals
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by dasimpson » Tue Jan 22, 2013 8:15 pm
btw you did not need to cut a hole in thwe case for that part of the lcd that part of the lcd is for 12 volt and can be cut off making the lcd pcb smaller
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by StevenPi » Wed Jan 23, 2013 6:18 pm
Hi :D
Yeah I saw those posts about the Ras-pi-gameboys which is where I got the idea.
I didn't know that I could cut off part of the board :o I thought they just released a newer model since mine looked different and that it was too bad for me :?

Well it's too late now anyways :P That was my first project I've ever tried and even though it looks really tacky and unprofessional, I'm still happy I managed to do that :D

In the future I'll do other things and as I get better and learn my projects won't be so tacky :)
For now I'm just relaxing and learning C++ and Python since I have no other projects currently in mind.
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by dasimpson » Wed Jan 23, 2013 6:35 pm
for mile i filled the holes were i messed up with epoxy resin and sand paper i aslo sanded the edges on the pi to make it fit the game boy case how i wonted my pi mods is this one http://www.retrovia.ie/showthread.php/1 ... pi-gameboy

i was going to go out of the top with the hdmi top so it could be hucked upto a hd screen for programming but i ended up leaving the lan on so i use ssh and made it so audio was out the top
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by dasimpson » Wed Jan 23, 2013 6:37 pm
with the programming hope you have better luck then me im trying to get the buttons working on the game boy so i can run an emulator and control the xbmc menus but man it is blagging my head
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by dasimpson » Thu Jan 31, 2013 12:07 pm
you could ethern run the pi and lcd on the aa battery conpartments this was an option i did not think of untill i had removed it
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