WTB UK: Short 25 Way male-male serial cables - Page 1
Forum section: electronics / general

author: dexters_lab
author_rank: Unknown
timestamp: December 03, 2018, 07:45:47 am
content: I need a pair of 25 pin d-sub male to male cables you would typically use on rs232/serial connections, so all 25 pins connected straight through, but they need to be short, maybe 30-50cm or sothere are loads of cheap ones on ebay but they all seem to be at least 2 meters long, the big suppliers like mouser do have some short ones but have astronomical pricing.... and i don't fancy making up my own!any ideas?

author: PlainName
author_rank: Super Contributor
timestamp: December 03, 2018, 09:43:09 am
content: IDC connectors with a bit of ribbon between them. Two mins to make a cable, max.https://uk.farnell.com/multicomp/8fsm25p-30n1-fec/plug-idc-d-unthreaded-25way/dp/1099300?st=idc%2025

author: dexters_lab
author_rank: Unknown
timestamp: December 03, 2018, 10:41:01 am
content: Thanks, yea i forgot about using IDCmy only concern is the interface it's being used on says it should be shielded twisted pairs as it runs at 27mhzi guess for the low cost it's probably worth a try

author: alanb
author_rank: Frequent Contributor
timestamp: December 03, 2018, 01:24:50 pm
content: Have you tried videk.co.uk. I've not dealt with them for a long time but in the past they had a great stock of some of the more obscure cables and connectors and on occasions have made custom cables for me.

author: PlainName
author_rank: Super Contributor
timestamp: December 03, 2018, 01:52:20 pm
content: You can get IDC twisted pair:https://uk.farnell.com/3m/3782-13p-270a/ribbon-cable-13-pair-per-m/dp/2064530?st=idc%2026%20twistedThose are connectable every 270mm, but 540mm are available according to the datasheet. You can even get shielded twisted pair, but I suspect the cost may be more than hiring someone to do the wiring for youWithout knowing your application, I suspect it's the impedance that's important here rather than the EMC abilities/susceptibility. Seven quid per two cables is a bit steep but might be worth it in the end.

author: dexters_lab
author_rank: Unknown
timestamp: December 03, 2018, 02:11:54 pm
content: it's a ccir656 digital video interconnectionthe pic is an original cable, i need a pair but only have one, so it's just to make up a whole new pair or replace the one i am missingi think i will make up some cheap ones using standard IDC like you suggested, then at some point in the future i can either find some short off the shelf cables or make up some proper ones of my own

author: stevelup
author_rank: Regular Contributor
timestamp: December 04, 2018, 10:47:09 am
content: Would be interesting to see inside one of those connectors!

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 04, 2018, 10:48:51 am
content: Quote from: stevelup on December 04, 2018, 10:47:09 amLooks like the back is filled with concrete? …

author: dexters_lab
author_rank: Unknown
timestamp: December 04, 2018, 11:00:57 am
content: yea, the back of the shell is covered in very thick and glued heatshrink with an extended tube, i am guessing the round block at the back is a ferrite

author: macboy
author_rank: Super Contributor
timestamp: December 07, 2018, 02:11:40 pm
content: Quote from: dexters_lab on December 03, 2018, 10:41:01 amI guarantee that serial cables are not shielded twisted pairs, it will be 25 individual conductors floating around loose and if you are lucky you will get a thin spiral of foil around it to give a little bit of shielding. If you really need impedance controlled twisted pairs, then serial cables won't work.The idea of twisted ribbon cable might work, this was used long ago for things like higher end SCSI cables for example. The problem is that with 25 conductors on the connector, you need to be certain about which pins are paired with which. twisted pair cable does you no favors at all if you split pairs!

author: dexters_lab
author_rank: Unknown
timestamp: December 08, 2018, 03:39:08 pm
content: i had a quick rummage around in my cable box and found a generic 2 meter 25 way male male serial cable to work with the genuine quantel cable, it seems to work fine so just using generic serial cables seems to be the best option.i also found these 1 meter serial cables on amazon:https://www.amazon.co.uk/gp/product/B002DELY88/ref=ox_sc_act_title_1?smid=A3P5ROKL5A1OLE&psc=1

author: SeanB
author_rank: Super Contributor
timestamp: December 08, 2018, 04:12:03 pm
content: Mark, I would hazard a guess that your video signal uses half the pairs as grounds for the shields, so just using regular ribbon cable will work over the half meter distance, though the twisted pair ribbon cable does give an advantage in that you can take the ribbon and fold it up accordion style lengthwise after the connector to make it more manageable and less of a dust collector, though it will be stiffer.Pity nobody makes an IDC connector that mates with the older 0.05in pitch that was used on IDE connectors which were ATA66 compatible, where half the pairs were grounded anyway and you got controlled impedances. However look for 25 pin 8 bit SCSI cables, those are available with short lengths and do have all pins connected with controlled impedance 110R cables. Would send you one but it is a converter, 25pin male one end and 64 way centronics the other, was used to connect a HP scanner to an Adaptec card, and also was daisy chained afterwards to an Arcus scanner and a Zip drive. Zip drive at the end because it was the one that had a built in terminator, and this was active as well, so as the other 2 only had passive termination options the zip drive got the honours. Inside the case the Deathstar was the other end, and it had a nice toasty passive terminator on the end of the cable.

author: dexters_lab
author_rank: Unknown
timestamp: December 10, 2018, 02:40:30 pm
content: Quote from: SeanB on December 08, 2018, 04:12:03 pmhey Sean, not seen to about much recently or have we just been in different parts of the forum!?it does indeed use lots of separate returns, i looked up a spec for bt.656 and proper spec cables are rated to 50 meters (!!!), so i think over short distances it will likely work with any old cablehttps://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.656-5-200712-I!!PDF-E.pdf(Appendix 1, bit-parallel interface)