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Author Topic: My serious fail with ribbon cable  (Read 986 times)
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I have a dilema.  I assumed (I know, I know) that an IDE cable would be one to one for every pin.  It turns out that this is not the case with the 80 conductor ribbon cable version of an IDE cable.  I have 40 pins from a shield that I built that I need to connect to another 40 pins on a TFT display.

Can anyone point me in the direction of a female to female cable that is 40 pins (with the standard header spacing)?  Or a good way to connect the two devices without single strands?

Thanks,

Loren
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Or a good way to connect the two devices without single strands?
The female connectors have "teeth" in them, that puncture the insulation of the ribbon cable.
That's why they're called "IDC", for Insulation-displacement connector.
So all you need to do is align them, then snap the bottom and top part, letting the "teeth" dig into the insulation and make contact with the conductor. No soldering needed.

You can buy these kind of female connectors from http://www.phoenixent.com/
For the cable, you can try eBay or mouser/digikey.

http://fabmodules.com/how-to-make-your-own-cable-10pin-female-to-female-ribbon-cable/

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I won a bid for one of these for a dollar! it's the standard jumper cables but all bound together in ribbon form.

http://www.ebay.ca/sch/i.html?_odkw=40+pin+female+dupont+cable&_sop=15&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0&_nkw=40+pin+1p-1p+dupont+cable&_sacat=0

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the 80 conductor ribbon cable version of an IDE cable.
What is this cable? The IDE is software it doesn't really have a cable, but if it did it would be the USB cable.

Oh hang on, IDC. Ok as vasquo says it's easy to make your own, get the parts and squeeze the halves onto the cable in a vice.

_____
Rob
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the 80 conductor ribbon cable version of an IDE cable.
What is this cable? The IDE is software it doesn't really have a cable, but if it did it would be the USB cable.

IDE, Integrated Drive Electronics, nowadays referred to as PATA, or Parallel ATA.  Wide, gray ribbon cable connecting your computer hard drives to the motherboard.  It's what was used prior to SATA drives became the norm.  40 conductors were for the longest time the standard before we moved to 80 conductors which were squashed dead when SATA came around.

You're thinking of IDE as Integrated Development Environment.  smiley
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You're thinking of IDE as Integrated Development Environment.
Quite right, at my age one's memory doesn't go back that far smiley

______
Rob
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I though IDE disk cables DID have 40 connections (40 pin connectors), although the more recent cables have 80 conductors. (half of the 80 conductors are GND and used for shielding, somehow "magically" connected at at least one end.)  Do the 80pin connectors have built-in connections for some of the other GND connections as well?
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Why not ask wikipedia?

http://en.wikipedia.org/wiki/Parallel_ATA#Differences_between_connectors_on_80-conductor_cables
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related note:

on a ribbion cable, you have a lot of capacative coupling wire to wire,

thats why half the pins are joined, to ground, so alternate conductors are ground, and alternat conductors are signal.

I've seen -5 v spikes coming out of 1 m of ribbion cable with insufficient earths, when the input is only + 5 volts .

its the edges.

oh BTW: the above blew the receiver circuit.
   the reason was that the pin numbering on the cable / schematic was wrong, so instead of alternate conductors in the ribbion being ground, 40 wires on the left were earth, the 40 on the right were signal !!
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The piece that I don't understand is that modern 80wire IDE cables still have 40pin connectors on each end.  So somewhere there is either "magic" to connect a bunch of the wires to GND, which might purposely connect other wires to gnd as well, OR it just leaves half the wires completely unconnected (they'd still shield things "some", maybe), in which case you really have a 40conductor cable.
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The piece that I don't understand is that modern 80wire IDE cables still have 40pin connectors on each end.  So somewhere there is either "magic" to connect a bunch of the wires to GND, which might purposely connect other wires to gnd as well, OR it just leaves half the wires completely unconnected (they'd still shield things "some", maybe), in which case you really have a 40conductor cable.


In the progress of building a 5x5x5 led cube I decided to use a 40 pin ribbon cable to make the connections from the standalone logic board to the led array. I used a 80 conductor cable assuming the 40 extra ground conductors would be no big deal as long as there was a one to one relationship to the 40 pin connector pins at each end.

 Bad assumption as the ground conductors connect to several pins on the connector and one ends up with not having 40 isolated conduction paths between the two connectors, but rather several shorted together paths, as there is not a single 'ground pin' assigned to those 80/40 cables. I at first though I might have miswired several connections to the mating connectors but after just replacing the ribbon cable with an older 40 conductor/40 pin ribbon connector I found all the problems were solved.

The thing with the 80/40 cables is that all 80 conductors are electrical connected in the IDC connector and there is direct electrical connections made between all of the 40 'ground shield conductors' with several of the 'primary' 40 pin connection pins, so one cannot use it as a 40 independent conductor cable.

I probably could word that better, but it gives me a headache just remembering about the troubleshooting problems I had with that cable when I was building my led cube.  smiley-wink


Lefty
« Last Edit: May 18, 2013, 04:46:39 pm by retrolefty » Logged

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That does state the basic difference/problem:

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Though the number of wires doubled, the number of connector pins and the pinout remain the same as 40-conductor cables, and the external appearance of the connectors is identical. Internally the connectors are different; the connectors for the 80-wire cable connect a larger number of ground wires to a smaller number of ground pins, while the connectors for the 40-wire cable connect ground wires to ground pins one-for-one.

Lefty
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Thanks.  That was the sort of detail (and actual experience) I was looking for.
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If 34 connections are all you need, floppy diskdrive cables will do the job, without the extra grounding wires.
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if u use a floppy cable, watch for the pin swapping.

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