ribbon cable mismatched with IDC spacing - Page 1
Forum section: electronics / projects

author: GregDunn
author_rank: Frequent Contributor
timestamp: March 07, 2019, 04:02:27 am
content: I'm making up a few GPIB cables for lab use and it seemed to be that the least hassle for quickly assembling and testing one would be to get some IDC 24-pin connectors, and ribbon cable which already has pins attached at one end (see image). That way I could quickly assemble the connector and plug the pins in a chosen order onto the microcontroller's standard female header to verify the pinout, instead of soldering and then having to make changes if the connections didn't behave as desired. Also fewer chances to short stuff together with solder drips or bridges.When I ordered the connectors, I found many suppliers which sold short lengths of ribbon cable with pin connectors already attached. I checked to make sure the spacing was specified as 0.1" (2.54mm) and threw a couple into the cart when I placed the order.Fast forward to the arrival of the parts. I quickly separated a 24-pin width of cable and made to place it into the IDC connector. You know where this is going, right? The cable was too wide for the connector. I pulled out a ruler and my calipers, both of which confirmed that the spacing of the wires was not the specified 2.54mm but actually 2.8mm. I actually ordered cables from a couple of different suppliers to increase the chances that I would get something usable, but all of them are the wrong spacing. I can lay them on top of my standard ribbon cables (which I've successfully used with IDC connectors) and they're clearly not the same spacingObviously, the cables are mis-represented in the description so I can get my money back if I care enough (a whole $3-4, whoopee) but my question is: am I likely to get this problem wherever I order pre-assembled ribbon cable segments? I already have roll upon roll of ribbon cable the right width, but it's just bare cable and I'll have to solder the other end anyway. Serves me right for trying to save a few minutes of tedious soldering, hey?

author: Buriedcode
author_rank: Super Contributor
timestamp: March 07, 2019, 05:07:18 am
content: Yeah.... IDC ribbon cable is 0.05" pitch, or 1.27mm because most IDC connectors are dual row. I believe you can get 2.54mm spacing cable for single row IDC, but that would be obvious as it would have large gaps between wires - unless each wire is 2.54mm in diameter which is silly. Like these for example:http://www.donconnex.tw/en/product-c34676/2-54mm-Ribbon-Cable-2-54mm-IDC-Connectors.htmlI assume the seller listed the pitch as 2.54mm because often these types of wire assemblies come in various connector sizes, 2, 4, 6, 10 etc.. as well as individual dupont connectors. So it was just a generic description for all types. Whilst one could argue it was misrepresented - if you wanted ribbon cable specifically for IDC's, then you should have searched for ribbon cable with that specific pitch. As far as I can tell it was never advertised as being 1.27mm pitch, and if a seller or distributor doesn't mention pitch, assume it isn't any kind of standard.

author: GregDunn
author_rank: Frequent Contributor
timestamp: March 07, 2019, 05:40:42 am
content: Well, I did specifically search for 0.1" / 2.54mm cable because there is a "standard" 2.8mm pitch as well. I double-checked the specific listing; I know searches often return spurious or incorrect details (I'd venture to say more than 90% of the time) and it specifies 2.54mm, multiple times in the listing. They don't even look the same as the bare cables, if you compare them closely. My guess is that if you choose the pin-terminated cables you get what they have, it's impossible to determine whether the cable is the correct spacing from the listing, and depending on the seller, maybe not even from contacting them. Too bad, but at least I won't waste any more money on this specific type. I know I can get the right kind of cable elsewhere, and I'll just have to make my own header terminations.Stripping ribbon cable and tinning the ends is good for the soul, right?Unrelated, it's sort of like the listings where you see "guaranteed delivery on x/xx/xxxx" but the item arrives days later. They're not coming from a major manufacturer/dealer with a reputation to uphold, and if you care you can probably get a refund or price adjustment, so it doesn't get a lot of visibility.

author: oPossum
author_rank: Super Contributor
timestamp: March 07, 2019, 06:31:53 am
content: Quote from: GregDunn on March 07, 2019, 05:40:42 amThey mate with 2.54 mm (100 mil) spaced headers. It's the connector pin spacing, not the cable lead spacing.

author: Seb71
author_rank: Newbie
timestamp: March 07, 2019, 11:44:14 am
content: Why don't you use "DuPont" connectors if you already have those pins crimped on both ends?