Wired version of DB9 Connector to PCB

gary · May 3, 2019, 1:33pm

I would like add a DB9 connector to a PCB but all I have is the wired version of the connector. Has anyone done this? Looks like the clearances will be tight but otherwise . . . ?

eelik · May 3, 2019, 1:48pm

We first had exactly this kind of connector but found one with THT pins and now use that. I don’t remember if I found out it was possible or impossible with the former. If you can fit it to a footprint which obeys manufacturer’s minimums, why not. At least it will be impossible to draw tracks between pins, so you must have enough room around it.

eelik · May 3, 2019, 1:52pm

I found this from the git history, it has much bigger holes than the current version. Maybe it was made for the wired version.

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Rene_Poschl · May 3, 2019, 1:59pm

As the through hole versions of these are quite readily available and are not really more expensive compared to wired ones i would highly advice against for using the tht version as you will get much better results with less work.

gary · May 3, 2019, 2:01pm

Thanks I will give that a try and let you know how it goes.
I did find the THT PCB versions just wanted to use these freebie parts rather than let them go to waste.
Perhaps I will find in the end that it was better to go with the ones designed for the PCB but not much to lose hear.

Rene_Poschl · May 3, 2019, 2:05pm

I guarantee that these will not go to waste. After all if you use sub d connectors on a pcb then you will for sure need one on the cable side as well (And if you do not need it now you will find a use for them later. Sub d connectors never lie around for long in my experience.)

gary · May 3, 2019, 2:13pm

Actually its a test interface, a one off. So barring repair I should not use them again as our production parts all use other styles of connections.
To your point though, I doubt they would truly go to waste as we would find some use for them but I also feel it might be just as hacky

SembazuruCDE · May 3, 2019, 3:05pm

For a one-off, this might be acceptable:
Use the solder-cup connector connected to the board with wires. Use any 9-pin (minimum) connector footprint (though a THT 9-pin d-sub footprint of the correct gender would help with disambiguation during wiring), and then mount the flopping connector to a bracket (3D printed? Cut from aluminum angle? Some other random prototype fabrication method?) that you connect to the board with some strategically placed mounting holes.

eelik · May 3, 2019, 3:33pm

LOL, forget that connector fp of mine. It was for 15 pin VGA, not for DB9. I just quickly looked into text files and didn’t check what it really was.

crasic · May 3, 2019, 4:55pm

Typically you solder or crimp, depending on style, these bad boys to pigtails and then solder wires to a plated hole , terminal block , or use another connector to attach to PCB. They sell pre pigtailed and precrimped ones for only a small premium to save you from making mistakes

They are useful in large chassis where either the run in longer or you do not want to mount PCB.

TH PCB style is not without it’s problems, they require good mechanical soldering and the mounting pads or can be ripped off the PCB by an angry or clumsy user. Sometimes a small daughterboard is used to hold just the DB9 and an internal harness to the controller board.

SMT ones also do exist, but they are more liable to break as well.

paulvdh · May 4, 2019, 10:11am

For a one-off I would simply solder short copper wires into the connector and solder those into the PCB. For a series I would definately get connectors that are made for PCB mounting.

A problem sometimes encounterd with sodering connectors inside PCB’s is that the contacts in connectors are often a bit loose, so they can align freely with their counterparts. By soldering them solidly into a PCB you obstruct that ability of the contacts to align.

Soldering the connectors while mated often makes this problem less severe, and also helps to keep alignment when plastic goes soft during hand soldering.

gary · May 4, 2019, 12:10pm

paulvdh,
This was the type of insights/warning I was looking for. How do they manage this in the pcb mounted ones which must be ridged? Tighter tolerance on the connector?

I think I am going to give this a try anyway and experience it all first hand anyway. Perhaps I will try slotted PCB holes to allow for alignment of the pins with the mating connector so as to limit the mechanical stresses.

Thanks for everyone’s feedback and I will post the results as I go along

SembazuruCDE · May 4, 2019, 6:19pm

Several points. Not all of them true all of the time.

Usually the PCB mounted connectors have long, thin solder tails that have a (small) amount of flex in them.
Usually the PCB mounted connectors will be mating with cable connected connectors that may have the “floating” self-alignment contacts.
Sometimes the self-aligning contacts allow too much float (usually the cheaper ones) and this is when you get crushed connector pins. (Not really that uncommon back when these connectors were more common on computers.)

If you are actually going to try soldering the solder-cup pins direct to the PCB, once they are soldered down then they will be locked into place. If you allow slop (excess mechanical tolerance) before soldering, the chances of the connector contacts being locked slightly out of alignment increases. Using oval (slot) holes is a bad idea.

I still think my suggestion (echoed both by crasic and paulvdh) of soldering wires to the connector and then soldering those wires to the PCB is the better solution. You just need to make a simple bracket to hold the connector firmly in space relative to the PCB to take handling stress off the wires. The simplest way to do this is with standoffs either mounted to mounting holes that you design into your board, or mounted to the same mounting surface that your PCB will be mounted to. All perfectly acceptable to one-off designs. (I wouldn’t want to use this for a production design unless I didn’t like my assembly team…)

EDIT: Completed my thought for the first sentence of that last paragraph… sorry about that.

Piotr · May 6, 2019, 10:18am

Many years ago we have done current loops in DB9 plugs. We are still using it. I made a photo:

The LED you see in it is used as Low voltage Zener diode. I’m not sure but as I remember there were two mechanisms of signal detection - one working when supply voltage got from COM was about 4…5.5V and next when 5…12V.

sam_moshiri · May 8, 2019, 7:45am

Are you bounded to use a serial port? if not, you can use a USB to Serial converter and even make your PCB smaller
if Not, there is another type of this connector with some Pins which can be mounted on the PCB, the same as motherboards serial ports
the idea of the Piotr is also good, all is up to you to decide

system · August 6, 2019, 7:45am

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