IEEE 1284 DB25 Wiring

[coasternuts]

I bought a straight thru DB25 cable, cut it in half, and started mapping the pins to the colored wires.  First thing I noticed was that there were 36 wires.  Curious, so I assumed some were common.  Using the multimeter I mapped from wires to pins and I found that for example the "White" wire was only mapped to pin 1.  I then hooked the male/female connector and tested the continuity between WHITE and WHITE on both ends, and to my surprise, other wires tested positive, not just WHITE, yet WHITE only mapped to pin 1!?!? 

1)  DB25 cable has 36 wires(18 twisted pair), of which, many are common
2)  There is not a 1-to-1 wire-to-wire when going across the connectors.
3)  There is not a 1-to-1 wire-to-pin

Are these facts true?  For those who use DB25 for quick disconnects, how did you find a unique set of wires and how many did you end up with?  At the rate I'm going it looks like I am probably going to get less than 25 inputs. 

I have searched the forums and I saw how one person indicated to mark the wires before cutting the cable, but that would not have helped here because the WHITE-to-WHITE also includes wires other than WHITE.

[tmasman]

You should be able to use ever pin...
You'll have wires left over, but there should be at least 1 wire for every pin. At least that was the case when I hacked a parallel cable... 

Even if there are multiple wires to pins, as long as you don't use any wires that point to multiple pins, you should be fine. Just double check that last catch multiple times...

But who knows, they are all different, & I'm no guru on that standard.

Good luck!

[cholin]

I was going to buy a DB25 too so Im glad this thread came up.  The wires should all be color coded and Im guessing the other wires are probably something to do with other signals through the cable, Im not sure.  If youre only using the cable for 25 inputs though, you could just cut the other wires right off because they are of no use to you, correct?

[coasternuts]

DOH! I'm a dork.  Imagine cutting and stripping all the wires so that you have this fountain of wires coming out of one end.  I was gator clipping one wire, not directly touching any others, and then using the test probe to discover the connections.  Of course alot of the wires are still touching each other ergo continuity.  I am currently taping down all wires individually to a table so no wire touches any other on both sides of the cut cable.  I'm assuming there will still be overlap but I should find individual inputs easier now.

[coasternuts]

After rigorous testing, I have come up with 18 unique wires, and the other 18 is shared.

So I guess I'll do 1 DB25 for each joystick/button player, which gives me (Left,Right,Up,Down, Start,Coin, GND, B1-8).  15 total.
.
I wanted to do DB9 for Optipac, (X1,X2,Y1,Y2,GND,+5,LB,RB) but I don't know if I can get each wire independent in a DB9 cable?  Also I assume on the optipac it would be ok to share +5,GND, is this true?

[cholin]

Im not sure about the last part, but why dont you make it easier and neater for yourself and use a standard ribbon cable (40 pin).

[coasternuts]

Just so I don't freak newbies away from DB25,  I bought some more of the same brand DB25 in different packaging, and to my surprise    there is 1 wire for every pin.  Also the gauge is slightly thicker.  Bonus!!  I am not regretting going DB25 now as I was before.

[ShinAce]

I bought a db15 monitor extension from the pace I work, and without even cutting it open, found it had 14 pins connected, individually.
But curiosity got the best of me, I just had to see the shielding.
It turns out the cable only has 1 shield covering all wires, which is perfect for me. And there are exactly 14 conductors. I'm using 13.

[nipsmg]

Weird.

My DB25 had 25 wires, all going to individual pins.
Go figure?

[Stingray]

Weird.

My DB25 had 25 wires, all going to individual pins.
Go figure?

So did mine.

-S

[Grasshopper]

I had a similar problem when I bought some 36pin to 36pin Centronics cables to connect my panel to my Ipac (I prefer Centronics connectors to DB25 as they are sturdier).

They were made by Belkin which is supposed to be a good brand. From my research I expected at least 25 separate connections but the cable only had about 18 or 19 (I can't remember the exact number). All the ground connections were joined together which, strictly speaking, contravenes the Centronics standard.

The only safe way to avoid this problem is to buy from companies that provide pinouts. I'd recommend Farnell for this (www.farnell.com). If a company won't provide pinouts then walk away. It's not worth the risk.