DB25 serial cable pinout?

Hi all,

After an hour of googling, I concede to ask this seemingly dumb question here;
How is a typical printer cable wired?

Is it as I suspect; 17 usable signal pins, and 8 pins that are clustered together to be used as GND?
Or are there components hidden in the connector? Are some wires crossed or is it a 1:1 patchcable?

I want to get an array of arduino outputs out to a junction box with relays and power sockets about 4 feet away, and I was wondering if I could just be lazy and use a standard printercable, or if I have to lop the connectors and solder my own.

A standard printer cable will have a 25-way D-sub connector at one end and a 37-way Centronics at the other end.

For obvious reasons it's wired straight trough, and it doesn't contain any circuitry.

If what you have is a 25-way D-sub cable with male/female connectors on it, it would probably be wired 1:1 but only a test with a multimeter can tell you if it is indeed fully connected.

// Per.

What he said...

DB25 to CENTRONICS LPT cable

The ones I have are LPT extenders, male and female D-subs.
Most diagrams suggest pin 18 ~ 25 are GND, does that mean they are all connected internally?

@raschemmel; So these cables DO have crossed pins?

I'm getting a lot of conflicting information when googling for DB25.
Some are crossed, some are patch, some are fully wired, some suggest there is only 13 usable lines.

I guess the only way to be certain is to either lop and resolder,
or to just measure what every pin does to every other pin.

Some DB25 cables are "serial" [u]null modem cables[/u] with some crisscrossed & jumpered connections.

With RS-232, of course you have to crisscross the TX & RX connections (and the handshaking connections if used). Sometimes the two devices are wired differently (DCE or DTE) and sometimes it's done with the cable or null-modem adapter.

LPT printer cable --- Centronics is your keyword
You probably want a DB-25M to DB-25F 25 lines,
wired straight through.

AnLPT Parallel printer cable is a STANDARD.
There should no conflicts.
They made gazillions of them, ALL THE SAME !

raschemmel:
ALL THE SAME !

Do a google search on DB25 pinout and tell me what you find.
There's apparently a billion different/custom types of DB25 cables.
So it's not as clear cut as you seem to suggest.

I've got a big box of printer cables still stowed away somewhere, a lot of which are M-M or M-F D-sub cables,
so I ill just attack them with a multimeter and see if I happen to have a fully wired DB25 in the mix.

Do a google search on DB25 pinout and tell me what you find.
There’s apparently a billion different/custom types of DB25 cables.
So it’s not as clear cut as you seem to suggest.

I’ve got a big box of printer cables still stowed away somewhere, a lot of which are M-M or M-F D-sub cables,
so I ill just attack them with a multimeter and see if I happen to have a fully wired DB25 in the mix.

You have 14 posts and you’re trying to tell someone with 14,000 posts what’s what ?
What’s wrong with you ?

DB25 is just a connector type.
LPT PARALLEL PRINTER CABLE IS A STANDARD.
That HAD to be all the same because the OS uses the standard.
As already explained , only one end is DB25, the other end is CENTRONICS.
You can’t have billions of different LPT parallel printer cables all using the same windows os.

The ones I have are LPT extenders, male and female D-subs.

OBVIOUSLY, db25 “extenders” are NOT LPT printer cables.

If you have a 100 LPT printer cables , they should all have a db25 at one end and a Centronics
connector at the other. What the heck do you need an ohmeter for ?
They’re all wired the same . How else would they work with the Windows operating system
that uses the LPT printer cable standard wiring ?

You started friendly in both of my topics, but you turned bitter in a heartbeat as soon as you found out i'm not some pedigree technician. Why are you being so hostile to beginners?

I'm just here trying to determine what cable will be suitable for my purpose, so if you're just looking for excuses to be mad at me, I implore you to go away.

The standard parallel printer connector is the 37 pin centronix. The use of a db 25 on PC's is an ibm pc abomination. Most cables with db25 connectors on both ends will be SERIAL cables, because that's what rs232 used before the pc started using the nine pin connectors instead.

Serial db25 csbles are indeed a swampland of non-standard-ness, with the full 25 wire straight through cable bring quite rare.

I guess the word "obviously" is your hotbutton.
If you don't want to be corrected don't post
incorrect statements. Where is the 'hostility' ?
All I did was correct you, which, truth be told,
is my job.

There is ONLY ONE LPT parallel printer cable
(DB25 to Centronics) . Abomination or not it
worked.

westfw:
The standard parallel printer connector is the 37 pin centronix. The use of a db 25 on PC’s is an ibm pc abomination. Most cables with db25 connectors on both ends will be SERIAL cables, because that’s what rs232 used before the pc started using the nine pin connectors instead.

Serial db25 csbles are indeed a swampland of non-standard-ness, with the full 25 wire straight through cable bring quite rare.

I’ve cracked open a few DB25 (I thought they were just called printer cable, my bad) a long time ago, and found that they had a bunch of resistors bridging pins as well as wires crossing, that’s why I came here with my question.

Is there perhaps a terminology for finding straight connected D-sub 25p cables?

raschemmel:
I guess the word “obviously” is your hotbutton.
If you don’t want to be corrected don’t post incorrect statements. Where is the ‘hostility’

You lorded your post count over me when I pointed out that your suggestion didn’t yield the result I was looking for, and on top of that you use ALLCAPS rather copiously as if you were yelling. All that leads me to believe you are rather quick to aggravate, or just out to stomp on the ‘noobs’.

Maybe im just misreading the mood, but I felt attacked by it.

I can't use bold or italics on my phone beause there's no toolbuttons so I have to use CAPS
for emphasis. Don't be so sensitive.

Is there perhaps a terminology for finding straight connected D-sub 25p cables?

Not really. Find a site that has a full spec sheet for the cable, like:
http://www.l-com.com/d-sub-premium-molded-d-sub-cable-db25-male-female-100-ft#

In today’s world of usb and cat5, it’s hard to remember how awful the state of db25 cabling used to be. I had it in a terminal server tutorial I wrote: “if it doesn’t work, it’s nearly alway the cable.”

raschemmel:
I can't use bold or italics on my phone beause there's no toolbuttons so I have to use CAPS
for emphasis. Don't be so sensitive.

I'm surprised you didn't know; You get the full suite of tools when you hit the reply button instead of using quickreply.

In regards to our unpleasant first encounter; I can give you my life story, but it basically boils down to me developing a tendency to be a bit cynical. So I'm sorry for overreacting. I'll try not to view your enthusiastic emphasising as demeaning from henceforth. Just be aware that your conduct might come across as a little crass to some folk.

westfw:
Not really. Find a site that has a full spec sheet for the cable, like:
http://www.l-com.com/d-sub-premium-molded-d-sub-cable-db25-male-female-100-ft#

In today’s world of usb and cat5, it’s hard to remember how awful the state of db25 cabling used to be. I had it in a terminal server tutorial I wrote: “if it doesn’t work, it’s nearly alway the cable.”

I briefly considered going with UART/SPI/I2C to get the data across, but that seems a little complicated just to control some relays 4ft away from the arduino.

In case my heaping box of spare cables yields nothing (usually the case), I went scrounging on ebay and found this one. I think the cable i'm after is referred to as "straight-through"?

Im also a little concerned the added wire resistance might muddle up the signal. Currently I have 220 ohm resistors on the output pins. Should I measure pin-to-pin resistance and compensate?

Surely if all you want to do is effectively move the serial connector from your PC back plane to be 2m or whatever nearer the printer, so you can plug the standard parallel cable into that, there must be no jiggery-pokery of the conductors in the cable. It must be straight through, and all that it must do is be a gender bender, so the far end of the new cable is the same gender as the PC, so that the printer cable can plug in.

I have been a forum member since 2013 so
I know what the toolbuttons look like because
I use them on my computer but as I said
they don't exist on my phone.
FYI, the cable you linked ("this one") is a SERIAL printer
cable and your post Title is "LPT parallel
printer cable" which , not to be cliche is
"apples" and "oranges" because the only
thing those two cables have in common
is the word "printer" in their name. Everything
else about them is different. Zapro's reply
(the first reply to your post) was correct.
He stated that the typical printer cable
(meaning the type of cable described by
your post title) has a DB25 at one end
and a Centronics connector at the other
end. The serial printer cable you just linked
is NOT the cable described by your post
titile because they are ad different as a
prop plane vs a jet plane. They might both
have wings and fly but other than that
they are very different, so now would be
a good time for you to set the record
straight. Are you talking about a Serial
printer cable OR the LPT Parallel Printer
described in your post title (the one with
a DB25 at one end and a Centronics
connector at the other ?
Did we waste all that time talking about
the standard LPT Parallel Printer cable
described in your post title ?
Is this entire thread about a straight through
serial cable instead of s printer cable
because you need an extension for the
DB25 printer output connector on your
computer ?

raschemmel:
Is this entire thread about a straight through serial cable instead of s printer cable because you need an extension for the DB25 printer output connector on your computer?

That's my take.

(PS I get that this goes under the heading of General Electronics, but General Electronics itself is under Using Arduino. I'm wondering where the Arduino fits into this discussion?)