Suggestions for smaller and low cost alternative to Ethernet connector - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: October 15, 2024, 03:06:05 pm
content: Hi,I am designing a PCB that has Ethernet running preferably at 100Mbps (but could limit it to 10Mbps) but, due to the limited space, I am looking for low cost, latching and more compact (!) alternative to the classic RJ45.Due to cost constraints in production, ideally it has an off-the shelf matching cable with an Ethernet connector on the other (I know very long shot!).Does anybody know if any such connector-cable solution exits?If not, any suggestions or ideas that meet the main criteria of low cost, latching and considerably smaller than RJ45?Thank you

author: artag
author_rank: Super Contributor
timestamp: October 15, 2024, 03:10:46 pm
content: There were once PCMCIA cards with tiny connectors, I think made by HRS or Honda.However they are a pain as they get lost. Most people preferred the cards with a standard connector even though it was big and stuck out a lot. But then you could take the card out.Can you use a standard connector that fits in the middle of the board thickness ? Sunken socket. These are lower profile. Alternatively, USB C and an external dongle. Apple do this.https://www.aliexpress.com/item/1005005899323204.html

author: mariush
author_rank: Super Contributor
timestamp: October 15, 2024, 03:22:10 pm
content: If you don't mind being limited to 100 mbps, you could use a 2.5mm TRRS audio jack - you only need 2 pairs for 100 mbps.I suppose eSATA could also work, it has 4 data pins and 3 ground pins ground, tx+/- , ground, rx+/-, groundFirewire is ancient enough that you could maybe use it, but not sure it has locking mechanism and it's not that much smaller.

author: ArdWar
author_rank: Frequent Contributor
timestamp: October 15, 2024, 03:26:55 pm
content: Quote from: artag on October 15, 2024, 03:10:46 pmHirosehttps://www.hirose.com/en/product/series/IXAlso, Harting ix:https://www.harting.com/en-US/s/harting-ix-industrial

author: reboots
author_rank: Regular Contributor
timestamp: October 15, 2024, 03:59:48 pm
content: How fast is your ethernet?JST has several different families of miniature latching connectors. PA (2.0mm) and GH (1.25mm) are two examples. They wouldn't be characterized for ethernet, but for low speeds (10Mbps) that probably wouldn't matter.https://www.jst-mfg.com/product/index.php?_search_product%3D%26_search_category_id%3D%26_search_feature_id%3D2%26type%3D3%26Digi-Key is your best bet for small quantities. They also carry pre-crimped leads for many of the JST contacts, which you might be able to use with a standard stranded-wire RJ45 connector.https://www.digikey.com/en/products/filter/jumper-wires-pre-crimped-leads/453?s=N4IgjCBcoLQdIDGUBmBDANgZwKYBoQB7KAbRABYBWSkAXQF9Gg

author: guenthert
author_rank: Frequent Contributor
timestamp: October 15, 2024, 04:01:35 pm
content: Quote from: mariush on October 15, 2024, 03:22:10 pmThe once popular (at home and office) 100BASE-TX uses 2 pairs, the more recent 100BASE-T1 (found in automotive and IoT applications) uses even just one. That has also the advantage that no connector is specified, so there's no expectations for any given.Generally speaking I'm not in favor of using an alien connector for any given purpose. There might be technical reasons (as in Ethernet) for a specified connector, but aside from that such can lead to mishaps. For Ethernet in particular you generally (if not in very specific, unchanging applications, like e.g. inside a vehicle) want the transformers ("magnetics") within the socket for galvanic separation.

author: ejeffrey
author_rank: Super Contributor
timestamp: October 15, 2024, 04:21:27 pm
content: Quote from: ricko_uk on October 15, 2024, 03:06:05 pmThat's a tall order. RJ45 is extremely low cost, and relatively compact for a latching connector. There are smaller options. Lenovo used to use a small connector with a breakout cable for Ethernet on their laptops that were too thin to use RJ45, but they weren't latching. I'm sure they were cheap for lenovo but I don't know if you can buy them in small volume. Now they just use USB to Ethernet adapters.Basically anything cheap is going to be reusing a high volume part. But the high volume option for Ethernet is RJ45. On a commercial product it's bad form to use a standardized connector for something non standard. For instance USB Type C and mini display port are cheap and easily could handle Ethernet but they will definitely cause customer confusion and off the shelf adapters are not widely available. Mini-DP does have a latching option although its uncommon.Single pair Ethernet checks all the boxes but it's not electrically compatible with standard twisted pair Ethernet. You need a different PHY and you need the link partner to also us single pair Ethernet.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 15, 2024, 04:23:31 pm
content: 100BASE-T can run over string (literally; well, saltwater-moistened string, of not too much length), don't worry about it. In particular, anything you do with a smaller connector, is likely to be strictly better than the signal quality from a normal 8P8C connector -- mainly because, if you're choosing your own type and pinout, you can resolve the stupid* 1-2, 3-6 pinning that became standard.*Various historical reasons, of course, but so it goes; that doesn't absolve it from being poor signaling practice. But still, baud rates are low, it isn't a long enough mismatch to matter.Any pin header will do; take your pick between size, cost and robustness.I'm currently somewhat "into" TE's HPI series; the 1.5mm pitch in particular, is easy enough to use but still reasonably high density. It is a bit fragile, not suitable for many insertion cycles, or much tension on the wires (which are thin, 28AWG), but that's fine for internal connections in commercial grade electronics.Tim

author: abeyer
author_rank: Frequent Contributor
timestamp: October 15, 2024, 07:55:10 pm
content: I don't know if/where you can still find them... but some pcmcia ethernet cards had low profile retractable rj-45 compatible connectors, that despite looking kinda flimsy always seemed to work really well for me.eg 3Com called theirs XJack:https://esaitech.com/products/3com-3cxfe574bt-10-100-ethernet-lan-adapter-pcmcia-card-w-x-jack?variant=41512498102435

author: ajb
author_rank: Super Contributor
timestamp: October 15, 2024, 09:16:32 pm
content: Quote from: ricko_uk on October 15, 2024, 03:06:05 pmAs others have pointed out, 100Mb Ethernet is pretty robust and forgiving of non-ideal wiring, so this connector requirement is really the hard part. 8P8C connectors are used for all sorts of non-Ethernet things, but finding one with a *smaller* connector on the other end is probably a tall order. Once option could be to use a short length of 1mm pitch ribbon cable, that can be inserted directly into an 8P8C plug and punched down, then just use a suitable 1/2mm pitch IDC ribbon connector on the PCB end. The wires won't be twisted over that length of wire, but if it's short enough you can probably get away with it. (I've used ribbon cable for short, flexible network test jumpers and they've been fine, credit to mikeselectricstuff for the idea.) Alternatively, a small PCB with an 8P8C jack and whatever other board connector of your choice...would be a bit more money, but gives a lot of flexibility.

author: ricko_uk
author_rank: Super Contributor
timestamp: October 16, 2024, 01:09:49 am
content: Thank you all!I assumed that 100 Mbps was very sensitive to impedance change that it actually is. A lot of useful info and possible solutions to look into.Thank you.

author: robzy
author_rank: Regular Contributor
timestamp: October 16, 2024, 01:20:45 am
content: This RJ11/RJ14 jack is the cheapest modular connector I could find on DigiKey that is "in stock", "normally stocking" and not marketplace:USD$0.30 in one off quantities:https://www.digikey.com.au/en/products/detail/adam-tech/MTJ-642BX2/9832240This is half the price of the cheapest RJ45 jack with the same criteria:USD$0.62 in one off quantities:https://www.digikey.com.au/en/products/detail/adam-tech/MTJ-881X1/9832263