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Lob0426
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Re: Plug-in Computing Cores/consolidated connector

Fri Aug 19, 2011 4:34 am

My post in How would you use a Raspberry Pi:
Sticking it (RasPi) inside a case that allows you to easily remove and install the SD card, through a slot in the case, would work well. Placing a connector on that case that will allow you to plug it into different interfaces. Plug it into a mini keyboard, battery and small LCD and it is portable. Plug it into a LAN/USB/power (model B) and you are ready to use it as a personal computing device on your desktop. Of course you will have to plug in a monitor when you need it. With only a few 4GB SD cards you could have half a dozen different uses for 1 or 2 (or 3) RasPi's. You can also hardwire from the SD card slot to the multi connector. Every time you plug into a different interface you would also be plugging into a different SD card. You just leave the appropriate SD card in the external connector.

In the Physical design thread I proposed placing a connector on one end of the board or case. In this connector would be 8 pins for Ethernet (6 needed for 10/100), 8 for USB (4 pins each port), At least 4 pins for power (2 power 2 ground), 3 pins for sound plus 2 pins for Composite video and 5 for the SD Card. Thats 30 pins in all. I would not try to convert the HDMI as I feel there is too much risk of damaging the board there. This is actually interesting in that with the SD card on the interface side of the connector you would only have to pull the "Computing Core", The RasPi, and replace it with another RasPi When the next versions come off the line you would add the connector to them. You would then have to unplug the old RasPi. replace it with the new version, then plug it back in. The software will be loaded from the SD card that is still in the connector. Granted there may be newer software that is needed for the newer version, but something like a server which is not really concerned with video probably will not even care. This could be done to a board by bolting a plate for the connector to it. Or attaching the connector to a case. You could pigtail all of the connections from the board to the connector if you did not want to go through desoldering and resoldering all of the connections.
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obarthelemy
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Re: Plug-in Computing Cores/consolidated connector

Fri Aug 19, 2011 6:37 am

I'd rather have standard connectors right off the main board, it's cheaper and more reliable. I don't mind spending all of 30 seconds swapping stuff over if/when I swap raspis, especially since, as you say, i might have to anyway.

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Lob0426
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Re: Plug-in Computing Cores/consolidated connector

Sun Aug 21, 2011 4:30 pm

This would be an avenue to pursue for such uses such as clusters or distributed computing. Clusters many times suffer when one device is not up to snuff. Being able to pull it and plug another in would be much easier when you consider all of the cabling involved. And that RasPi will be useful elsewhere. In a distributed system such as home automation, each device will have a different set of instructions and possibly different hardware requirements. Again, being able to just pull the RasPi and plug in another one would be real convenient. Another reason is so one device can be used for multiple uses, though a RasPi is cheap enough that I really won't use it this way.
Of course the best way to do this would be to bring this all to a card edge or connector not with wires (interference). This would also work well for those of us that intend them for projects.
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Lob0426
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Re: Plug-in Computing Cores/consolidated connector

Sun Aug 28, 2011 10:14 pm

I believe I have found a winner for a test of building a universal connector for the RasPi.
http://www.tigerdirect.com/app.....8;CatId=82
Yep its an ATX extension cable. Male and Female 24 pin connectors. It only actually has 22 wires in it.
4 for Ethernet
2 for power
8 for USB
3 for sound
17 total

9 more for the SD card
If I decide to put the SD card on the connector I will have to delete the sound and come up with another wire.
23 total
once I get the connector wired I will shrink wrap the whole board in model airplane covering. It is amazingly tough and comes in all kinds of colors.

I will probably buy four extensions so I can have three to experiment with a one to steal wires out of.
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Blars
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Re: Plug-in Computing Cores/consolidated connector

Mon Aug 29, 2011 12:30 am

Ethernet needs to be twisted pair, usb should be sheiled twisted pair, sound should be sheilded. You can probably use the same power lines for both usb though. looks like asking for trouble.

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Lob0426
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Re: Plug-in Computing Cores/consolidated connector

Mon Aug 29, 2011 1:29 am

I planned to use CAT5E to the connector anyway for Ethernet (two pair). The USB I forgot about it being shielded but it probably would work. Usually USB has no problem but causes problems. USB sticks can be pretty "noisy". I have not seen it as twisted pair though. But I don't doubt you. I have USB cords lying around but I could use the CAT5E for that also to the connector. The sound will probably be just fine over the 3 inch length to the connector. The power at this point is 12v so no luck there. The biggest problem is the difference in wire size.

I really do not foresee too much trouble as the wire lengths are so short. Running the wires under the board will help some also. Remember the whole board is only going to be credit card sized. The real way to do it would be a card edge for it all. Trace lengths might be to long for good performance . The other ends of these wires are going to be soldered. A lot less noisy than the connectors are. The only real worry I see is If I bring out the SD card. I have no idea how noise sensitive they are. An indication might be that they work just fine in a USB adapter.

Maybe thats why its called an experiment. lol. Thank you for the input.
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Lob0426
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Re: Plug-in Computing Cores/consolidated connector

Sat Sep 17, 2011 10:21 pm

I have been working on this a bit and here is what I have come up with so far for parts for the test rig.

A Radio shack Male crimp DB25 connector

image removed as it represented the solder cup female connector.

And of course a DB25 Female connector


For now I have decided to keep the power connector seperate, Though I would like to include it in the end connector.
I also bought a pin extractor set.

The reason I started this with crimp connectors is because you can, with effort, remove the pins. If I find the layout is causing interference I can move the pins around to try to reduce it or eliminate it. This would be very tedious with solder cup connectors. The final hardware will be solder cups. In the test piece the connections to the RasPi will be by appropriate connector pigtail cords. I will cutt off a length of a USB or Ethernet cord with connector then strip and crimp into the DB25. In the Final hardware I will most likely remove trhe connectors from the RasPi board and Solder directly in. I believe hardwiring is ultimately the smartest way to go. I have kept the power seperate for now as this will let you plug and unplug power without unpluging the DB25.

EDIT: actually PHASE 1: get a RasPi. lol

PHASE 1: use the crimp connectors to already corded connectors for interference testing. This way you know you have certified cordage and connectors. You also know you have a working Raspberry PI. TEST, reorder the pinned wires as necessary

PHASE 2: Remove connectors from RasPi board and Solder in the SAME cords you just tested with connectors as hardwired to RasPI. TEST

PHASE 3: Replace DB25 crimp connectors with solder Cup connectors. TEST

PHASE 4: develop a mounting system for the Raspbeery Pi board. At this phase I will look towards using a PCB mounted DB25 female connector, and possibly a Power connector and switch, on a PCB board that will be bolted to the underside of the RasPi board. It may be possible to have all of the functions exit the "VIDEO" side of the board. The primary idea currently is to have the Video at one end and everything else on the other end of the board. TEST

Finished product should be able to be easily disconnected and moved to another similar connection. The male connector can be configured for each individual use. The female, or RasPi side, of the connector will always be wired the same way. This will, if it works out, cure the complaints of the connectors exiting every side od the board. This will help many project builders.
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Lob0426
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Re: Plug-in Computing Cores/consolidated connector

Sun Sep 18, 2011 7:29 pm

I am surprised that this thread has not seen more activity. There have been many posts about building the RasPi with an edge connector. This is an alternative that will work if properly implemented.

Ethernet is twisted pair and unshielded.
USB is shielded but not twisted pair.
Audio and power are not shielded or twisted.
I have not found any cabling requirements for SD card but is that surprising?

I am open for suggestions as to cabling any of the last three to the DB25 connector. I am thinking about using USB cord for the audio since it is shielded. I am not so worried about it causing interference, but it is susceptible to interference. The power should be clean except if it is a poorly made adapter. As to the SD card I think it could be a problem either way. I have noticed that USB sticks always caused static on the audio if they are right next to the audio connector. I assume the SD card could have similar problems. So I am looking for a shielded cabling for it. In my initial tests I will not be wiring in SD to the DB25 connector. Later I do intend to give it a try.

Careful grouping of pins is going to have to be done if interference is going to be avoided.
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