0.156" Pitch Header - Page 1
Forum section: electronics / projects

author: NivagSwerdna
author_rank: Super Contributor
timestamp: September 21, 2020, 06:47:19 pm
content: I'm trying to create a footprint for a PCB that will connect to a 12x2 female 0.156" edge connector...... got me thinking...Why 0.156"? Where did that come from?

author: Benta
author_rank: Super Contributor
timestamp: September 21, 2020, 06:58:12 pm
content: Good questionIt was very common for single board computers in the 1970s/80s, but whoever defined it? No idea.

author: Ian.M
author_rank: Super Contributor
timestamp: September 21, 2020, 07:07:07 pm
content: 5/32" rounded to the nearest mil. On a 50 position connector the difference between 5/32" and 0.156" pitch at the last position is less than 8% of the pitch.Why 5/32" ? Well that was probably down to constraints like track spacing and required track width for whoever had the original application, then everyone else jumped on the band wagon once a connector was available.Edit for clarification: 'mil' is very much a USAism for what the rest of the world used to call a 'thou', namely a thousandth of an inch.

author: coppice
author_rank: Super Contributor
timestamp: September 21, 2020, 07:11:38 pm
content: Quote from: Benta on September 21, 2020, 06:58:12 pmIn the early days of PCB edge connectors they all seemed to be 0.156" pitch.

author: Pawelr98
author_rank: Regular Contributor
timestamp: September 23, 2020, 03:16:47 am
content: I happen to have a soviet VFD display board that uses 2mm/4mm pitch.Made in 1976.0.156" is roughly 4mm.USSR commonly used 2.5mm pitch instead of 2.54mm because they didn't want to use inches.So with the 0.156" they decided to round it off to 4mm.Must have been some common standard back then, if the USSR used similar dimensions.

author: tkamiya
author_rank: Super Contributor
timestamp: September 23, 2020, 04:26:01 am
content: In Japan, standard spacing for analog board was 4mm. In earlier days, there were ICs made with 2.5mm but it didn't last long. Eventually, market demand dictated we'd start using 2.54mm US standard.

author: Berni
author_rank: Super Contributor
timestamp: September 23, 2020, 05:16:45 am
content: Sounds just as infuriating as the zoo of SMD chip pin pitches these days:- 1.5 mm- 1.27 mm SOIC okay so half the DIP makes sense- 1.0 mm- 0.8 mm- 0.75 mm- 0.7 mm- 0.65 mm- 0.6 mm- 0.5 mm- 0.4 mmI probably forgot some but everyone seams to just pick some random pin pitch for the small SMD chips or connectors.Then you still have some connectors that use 2.5mm and 5mm (Like JST for example)

author: bsdphk
author_rank: Regular Contributor
timestamp: September 23, 2020, 07:00:01 am
content: I had the very same problem recently, creating an extender-board for a Documation M200 punched card reader.The relevant mil.std is 21097 which has all the dimensions for the connector you slot the PCB into, but surprisingly nothing even remotely like a PCB-footprint. In particular you will want to look at the "M21079" documents.The only place I found guidance on the PCB footprint was in old versions of EDAC's 307/357 series datasheet.A really good "app" to supplement KiCad would be a edge-connector footprint generator, either as stand alone (python?) code, or as a webapp.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: September 23, 2020, 09:23:48 am
content: Quote from: bsdphk on September 23, 2020, 07:00:01 amFunny you mention that because the MIL Spec was one of my google-ings...It contains a table which defines 0.050, 0.075, .100, .125, .156, .200 being contact spacings in inches (with approx metric equivalents) and that the error should be +/- 0.005 non-accumulating.So I think that definitely defines it as exactly 0.156" centered spacing... I'm now looking at IEEE488 plugs... what a minefield.

author: tkamiya
author_rank: Super Contributor
timestamp: September 23, 2020, 02:14:29 pm
content: It's really annoying when I guess wrong and things ALMOST fit.....

author: bsdphk
author_rank: Regular Contributor
timestamp: September 23, 2020, 07:24:31 pm
content: that sounds like a CBM project to me :-)For the IEEE end, buy a used cable on ebay, and chop one end of.