28pin IDC / ribbon cable conectors do not exist?  - Page 1
Forum section: electronics / projects

author: Yansi
author_rank: Super Contributor
timestamp: December 02, 2018, 04:33:00 pm
content: Hello,just evaluating a possible project of ROM emulation, which requires to replace functionally a 28pin DIP IC. I thought well, easy enough, I can use a flat ribbon cable PCB connector and stick it in instead of the original chip, then use a 28pin ribbon cable and terminate it in the other PCB using ... well a 28pin IDC socket.Unfortunately it seems 28pin IDC sockets (either PCB or for the cable) like these do not exist, wtf?! Or have I just not looked hard enough?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 02, 2018, 05:09:45 pm
content: So use a 34 pin one.

author: Yansi
author_rank: Super Contributor
timestamp: December 02, 2018, 05:22:47 pm
content: Wouldn't that look kind of .. lame? having a 34pin IDC connecter, while only 28 pins would be used? (On the other side, I could place there some signals "reserved for future use"..)Or are there any other connector options for flat ribbon cables, that would play nicely with 28 pins?Thanks

author: ejeffrey
author_rank: Super Contributor
timestamp: December 02, 2018, 06:44:56 pm
content: If it works and is easy and uses off the shelf components, do you care?

author: cdev
author_rank: Super Contributor
timestamp: December 02, 2018, 07:14:53 pm
content: Add more grounding and power if its needed. Space the grounds every few pins to reduce RFI.

author: wraper
author_rank: Unknown
timestamp: December 02, 2018, 07:21:26 pm
content: Quote from: Yansi on December 02, 2018, 05:22:47 pmAnd what about using MCU or any other IC with leaving half of the pins left unused. Would you go through hoops just to use one with lower pin count?

author: Benta
author_rank: Super Contributor
timestamp: December 02, 2018, 07:22:32 pm
content: Quote from: cdev on December 02, 2018, 07:14:53 pmUmm.... No.On the one end you have a 28-pin IDC DIP header, on the other a 34-pin IDC connector.Standard solution is to use a 28-lead flat cable with the "1"-lead/pins aligned. This will give 6 empty positions on the other end of the IDC connector. Absolutely standard practice and will not look out of place.

author: electrodacus
author_rank: Super Contributor
timestamp: December 02, 2018, 07:31:51 pm
content: They do exist but are not very common so maybe 26 or 30pin ones can work for you.

author: Yansi
author_rank: Super Contributor
timestamp: December 02, 2018, 07:37:32 pm
content: At least Benta understands how does a ROM emulator look like. Thanks.Quote from: ejeffrey on December 02, 2018, 06:44:56 pmI care about my stuff a lot, you do not?Quote from: wraper on December 02, 2018, 07:21:26 pmYes, I would. Every serious designer should.I am sorry guys, but I am not supporting today's "arduinist devil clan" by producing more and more half-thought garbage.Quote from: electrodacus on December 02, 2018, 07:31:51 pmThank you for pointing out TME, I was looking only on Mouser for them so far. If they can be bought for reasonable price, I will definitely use 28pin ones, as the device will both interface 28 and 24 pin sockets. Leaving 34-24=10 pins unused in the latter case would be just awful.

author: wraper
author_rank: Unknown
timestamp: December 02, 2018, 07:44:07 pm
content: Quote from: Yansi on December 02, 2018, 07:37:32 pmIf there are no benefits and even downsides such as higher cost or poor availability with using lower pin count IC, no designer should bother. Smart engineer won't use obscure part just because it has lower pin count.

author: Yansi
author_rank: Super Contributor
timestamp: December 02, 2018, 07:49:46 pm
content: Yes, there is a benefit, because a 34pin IDC connector on an instrument with only 24 or 28 pins used looks like aI would also like to ask youwraperif you do not have anything to sayto the topic, please keep your fingers out of the keyboard.

author: wraper
author_rank: Unknown
timestamp: December 02, 2018, 07:55:10 pm
content: Quote from: Yansi on December 02, 2018, 07:49:46 pmAs already said, use them for GND and power. Nobody would even notice. If you design in something obscure, there are high chances people will curse you later.

author: wraper
author_rank: Unknown
timestamp: December 02, 2018, 07:59:23 pm
content: Quote from: Yansi on December 02, 2018, 07:49:46 pmYeah, and arguing that unused pins are ugly is certainly very important and useful.

author: Benta
author_rank: Super Contributor
timestamp: December 02, 2018, 08:35:01 pm
content: Quote from: Yansi on December 02, 2018, 07:49:46 pmI appreciate that for you it's an aesthetic problem. On the other hand, this is done all the time, and has been for the last 30 years.Another aspect: there are also 32-pin DIP ROMs, are they out of scope?. Personally, I'd go for the 34-pin IDC. Easy to source and cheap.