Good PCB connector (SMD) for UART/Programming interface - Page 1
Forum section: electronics / projects

author: espena
author_rank: Contributor
timestamp: April 30, 2024, 04:14:55 pm
content: I'm looking for a good 4-wire, surface mounted PCB connector (male and female, wire-to-pcb) that can be easily attached and detached without requiring excessive force or tools.It's for connecting my programmer to a MCU UART interface. It's a prototype, and there will be many cycles of connecting and disconnecting the programmer. No high frequency stuff, so shielding is not required. A straight pin header with female counterpart kind of works, but it tends to wear out quickly. The connections get unstable over time, leading to disrupted programming cycles.So I wish for a contact pair that doesn't lock on too tight, still being reliable enough for my purpose. Preferably with orientation guides. Both 1,27mm or 2,54mm pitch will work.I've been trying to find something on Mouser, but there's a jungle of options. So, your suggestions will be appreciated in order to narrow my search a bit.

author: Retirednerd2020
author_rank: Regular Contributor
timestamp: April 30, 2024, 04:42:41 pm
content: For products that I knew would be continually developed over quarters or years, I've used pads on the board and spring-loaded pogo-pins on a jig. I would also bring out some other important signals to external connection points. The jigs were generally simple to make and use. This is essentially free (wrt. the product cost) and can use zero board space.For prototypes that might only take a few weeks or months, then done, I would often just use a small smt 2mm x 2-row, unshrouded connector that mated with the programmer's ribbon connector. The programmer was never disconnected and stayed with the product throughout the development. If the product was cost sensitive, the connector would not be populated in production.I don't recall ever wearing out a connector although I have broken wires that came from the programmer.

author: max_torque
author_rank: Super Contributor
timestamp: April 30, 2024, 06:16:51 pm
content: I'm going to assume that you don't need "low cost" as one of the options as you mention it is for primarily dev workThe "trick" in my experience to to use a connector sytem where the male pins are on the pcb and the female ones on the harness, and then use an adaptor harness to another connector that suits your programmer or programming hardware interface etcThis means the pins of the connector half which is soldered to the pcb itself, and therefore annoying/difficult to replace, don't wear out much (solid pins are tough and resillient) and the interface harness can be connected to the programmer once and left connected, and then really the bit that wears out are the female contacts in the socket on the end of that adaptpr harness, as these are the ones being mated/unmated regularily and getting bent & abused etc.I use Molex Picoblade SMC series connectors, usually in 8 way format, and the right angle and straight version share the same pcb footprint, so you can install which ever works best to have the programming connector coming off the board at right angles or horizontally. The connector has a strong latch so it's reliable enough for bench work, but not so strong you can't pull it out before you damage the halfs or peal the connector assy off the pcb. They are pretty cheap, and with the 8 way version, i can include debugging coms (UART etc) and have a standard pin out for all projects. This 1.25mm pitch means even 8 pin in a row is stil pretty compactWhen the female contacts in the adaptor harness finally get too loose and un-reliable, i just bin that bit and make another adaptor harness to suit what ever the programmer requires (JTAG 2x10 etc) depending on what micro/programmer is being used.https://www.molex.com/en-us/part-list/53261?taxonomyPathValueLast=PCB%20Headers%20and%20Receptacles

author: max_torque
author_rank: Super Contributor
timestamp: April 30, 2024, 06:18:34 pm
content: BTW, for production, i have actually managed to use the standard footprint "pads" for an unpopulated picoblade as pogo pin footprints. It required a jig to hold the pcb and pogo's but that's pretty easy to arrange, esp with a bit of cheap 3d printing these days. That means you have no cost for the programming connector in production

author: tszaboo
author_rank: Super Contributor
timestamp: April 30, 2024, 08:56:53 pm
content: You can use Tag-connect pads and programming pins as a near zero cost programming solution to your product.

author: thm_w
author_rank: Super Contributor
timestamp: April 30, 2024, 09:38:08 pm
content: Quote from: espena on April 30, 2024, 04:14:55 pmUse better quality headers and connectors.

author: PlainName
author_rank: Super Contributor
timestamp: April 30, 2024, 09:48:52 pm
content: Quote from: tszaboo on April 30, 2024, 08:56:53 pmWorth noting that they do latching versions of these too (so they remain attached to the board while you use you had for other stuff). Downside is they take up a bit more space than just the signal pads alone, and the alignment holes get in the way of tracking sometimes.

author: espena
author_rank: Contributor
timestamp: May 14, 2024, 07:11:48 pm
content: Many great suggestions, thanks a lot! Went for a magnetic pogo pin solution, but will try out the tag-connect pads in a later project!

author: S. Petrukhin
author_rank: Super Contributor
timestamp: May 15, 2024, 09:27:11 am
content: I use a plug to connect the programmer and the console UART, which does not require a mate, it is simply inserted into a bare PCB.It's a little bulky, but I've come to terms with it.Phoenix Contact SDDC 1.5/4-PV-3.5 P/N: 1848668https://www.phoenixcontact.com/en-us/products/pcb-direct-plug-sddc-15-4-pv-35-1848668

author: luudee
author_rank: Frequent Contributor
timestamp: May 15, 2024, 09:42:11 am
content: I have used POGO connectors before, but dislike them now very much. To flimsy, unstable and bad connections. Constantly poping of the PCB.And we were buying the original, expensive ones from Tag-Connect.Now we use the clamps, like in the attached picture. Get them from AliExpress, can also buy spare replacement pins.They come in many configurations, 1.27 mm, 2.00 mm, and 2.54 mm ...They are dirt cheap and so far have been lasting for years without any issues. We use them for both,UART and programming ...Cheers,rudi

author: S. Petrukhin
author_rank: Super Contributor
timestamp: May 15, 2024, 10:00:03 am
content: Quote from: luudee on May 15, 2024, 09:42:11 amThe clothespin on the edge is inconvenient to use when the PCB is in the housing. Isn't it?Usually the edge of the PCB is close to the wall of the housing.I tried to do this by using hooks to insert from the top, not from the side. But it turned out to be unreliable.Sometimes you have to connect to equipment in the fields, the programmer is hanging on a wire, connected to a PC via a heavy USB extension cable...

author: mariush
author_rank: Super Contributor
timestamp: May 15, 2024, 10:11:36 am
content: you could just use a RJ45 connector without magnetics built in.. cheap and easy to replaceexample :https://www.digikey.com/en/products/detail/assmann-wsw-components/A-MJH-8-EA-GTP-W4/20522480The specs says minimum insertion count : 750 ... kinda low, but then again you can replace it easily, and ready made ethernet patch cables are equally cheap.RJ11 is also cheap, here's one with 4 pins :https://www.digikey.com/en/products/detail/adam-tech/MTJ-642BX2/9832240What else ... classic audio jacks ... TRRS jacks have 4 contacts ... make it ground, tx , rx , voltage to minimize risk of shorts and you have jacks with 5000+ insertion cycles and small footprintSeehttps://www.digikey.com/short/ztj33h2hfor jacksyou can also get ready made cables, for example3.5mm :https://www.digikey.com/en/products/detail/tensility-international-corp/10-02133/7606582and2.5mm :https://www.digikey.com/en/products/detail/tensility-international-corp/CA-254S-M-M/382909

author: S. Petrukhin
author_rank: Super Contributor
timestamp: May 15, 2024, 10:22:03 am
content: A couple of photos