EEVblog #1262 - Designing a Flex PCB + uSupply Update - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: November 15, 2019, 09:48:05 pm
content: Designing a flexible PCB adapter board for the uSupply project.Discussion of rigid flex PCB design, layout, and manufacturing.Plus a rant on ST Micro parts and USB Power Delivery.

author: jazz
author_rank: Contributor
timestamp: November 16, 2019, 12:29:37 am
content: Nice to see the progress on the uSupply.I know you're planning to use a custom LCD on it, but the renderings made me wonder. Did you choose the custom LCD dimensions to be similar to some easily obtainable colour dot matrix LCD, so if you should ever want to do such an LCD upgrade, you could reuse the case without much trouble? Or did you select the LCD dimensions more or less at random, without anything like that in mind?Also, does David2 get paid by the hour to work on the uSupply, or does he actually have a stake in it and gets a percentage of the revenues?

author: sakujo7
author_rank: Contributor
timestamp: November 16, 2019, 01:15:42 am
content: I'm very curious as to why this mega-library is so big. Anyone got a link to it? Found very little on google.Edit: Found the part of the video mentioning closed source and undocumented registers, wtf? Why even have a (partial) register listing if the only realistic way of getting it working is a bloated binary blob?

author: FrankBuss
author_rank: Unknown
timestamp: November 16, 2019, 01:28:17 am
content: I wonder if there could be a problem for the 8 MHz crystal with the long traces on the flex PCB. Usually the app notes say to place it as close to the IC as possible.

author: sakujo7
author_rank: Contributor
timestamp: November 16, 2019, 02:41:28 am
content: Had a quick look at the USB PD specification... it's 657 pages! Pretty crazy when the most common use case is just switching from 5V to 9V.The latest revision supports 3.3V to 21V programmable voltage and current limits... You could probably make a "uSupply lite" that's just a controller with no regulation...

author: langwadt
author_rank: Super Contributor
timestamp: November 16, 2019, 02:47:53 am
content: Quote from: FrankBuss on November 16, 2019, 01:28:17 amyes, should probably have had the crystal and some decoupling caps on the flex

author: Nominal Animal
author_rank: Super Contributor
timestamp: November 16, 2019, 03:10:16 am
content: This is probably an utterly silly question, but why not put the adapter PCB between the board and the existing components?There aren't that many, so unsoldering them, soldering the board, then adding the components on top, should be doable?

author: Unixon
author_rank: Frequent Contributor
timestamp: November 16, 2019, 08:19:37 pm
content: Dave, There's a better way to solve this with a rigid patch than attaching flex PCB, but only if boards aren't assembled yet.What you basically do is design a new version, then cut out a minimal piece of project and move it to a patch board. Existing pads covered by a patch PCB go to the bottom layer of the patch thus making an LGA-type package, replacement circuit goes to the top layer. In worst case a 4-layer patch PCB may be necessary to do all connections, but in this case you can probably get away with a 2-layer patch board. However, it may be difficult to align a patch board perfectly with fine pitch bottom pads.

author: vanarebane
author_rank: Contributor
timestamp: November 16, 2019, 08:59:42 pm
content: Add that bypass cap on the FPC

author: Fran_PSR
author_rank: Newbie
timestamp: November 16, 2019, 10:45:35 pm
content: As always an excellent video, very didactic and entertaining. Now I have a question. I see that the film has some pads to connect the two-sided tracks. Is there a risk that those pads make contact with any component that is on the pcb?Thank you

author: EEVblog
author_rank: Unknown
timestamp: November 17, 2019, 08:39:39 am
content: Quote from: Fran_PSR on November 16, 2019, 10:45:35 pmI mentioned that in the video. One of the reasons to tent the vias.

author: EEVblog
author_rank: Unknown
timestamp: November 17, 2019, 08:40:17 am
content: Quote from: Unixon on November 16, 2019, 08:19:37 pmThey are assembled and that's the whole point.

author: Unixon
author_rank: Frequent Contributor
timestamp: November 17, 2019, 09:07:44 pm
content: Quote from: EEVblog on November 17, 2019, 08:40:17 amWell, that's unfortunate. At least you may try to flip this chip-on-flex on its top and glue with epoxy back to the same spot to save height.BTW, why do you need a proper USB PD and why the hell these libraries so huge?

author: Paul Bryson
author_rank: Contributor
timestamp: November 17, 2019, 10:58:33 pm
content: I had a similar problem and came to a similar solution. I also performed a few experiments to try out different techniques.You can see my results here:http://www.brysonics.com/we-dont-need-no-stinking-bodges/

author: German_EE
author_rank: Super Contributor
timestamp: November 18, 2019, 12:33:07 pm
content: OK Dave, thank you for another exercise in PCB design, useful and also entertaining.HOWEVER...............................................I can live with most of your catch phrases, but if you use the 'Polly put the kettle on' phrase to describe a piece of plastic once more I will jump up and down on your head until the squishy bits come out.Thank you.

author: fmiz
author_rank: Newbie
timestamp: November 19, 2019, 01:04:02 am
content: Quote from: German_EE on November 18, 2019, 12:33:07 pmI thought that he was being serious and he was saying the name of a specific material, then a generic one (polyamide), and I just gave up trying to understand what he was saying because of how fast he can say 'Polly put the kettle on'! You gotta be shittin me, bloody catch phrases! I'll just trust that it's a joke, no worries! It's a trap for non-native speakers, beauty!German_EE let's meet on our way there

author: thm_w
author_rank: Super Contributor
timestamp: November 19, 2019, 10:36:48 pm
content: From the recent Great Scott video I managed to locate this adapter:https://www.ebay.com/itm/Super-Mini-ZYPDS-DC-mini-20V-trigger-support-millet-65W-PD-power-supply-/132714794782Which is intriguing as its using a single TSSOP part (no PD chip, they have other devices with the PD ICs too). I don't see any markings, it could be a micro or a standalone PD IC.Also it is only capable of 15 or 20V, not sure if that was intentionally chosen or a limitation of the IC.Quote from: sakujo7 on November 16, 2019, 01:15:42 amThe STUSB1602 library fits in about 45kB or so, you can find it here if you want to look:https://github.com/st-one/X-CUBE-USB-PDA lot of it is the USB comms itself, the PD stuff doesn't look too big.But anyway, as mentioned above, PD covers a LOT and implementing all of these options in a library takes space, even if you only use one of the features. Sometimes the compiler can strip out the unneeded stuff and save space, but it depends how its been written.Quote from: Paul Bryson on November 17, 2019, 10:58:33 pmTQFP one is awesome.For a single line of pads, small LCDs seem to have standardized on a pad with a via or two that worked well when I tried it:https://imgaz.staticbg.com/images/oaupload/banggood/images/C1/CA/42bf26a4-a71a-46d1-a09e-f3abf4ed7ceb.JPG

author: Xenoamor
author_rank: Regular Contributor
timestamp: November 22, 2019, 05:02:25 pm
content: Definitely hyped for more uSupply videos!

author: Nominal Animal
author_rank: Super Contributor
timestamp: November 23, 2019, 02:53:18 am
content: Quote from: German_EE on November 18, 2019, 12:33:07 pmWhile you're there, would you mind tellingStefanGotteswinterto pronounce surface as "sur-fis" (/'sɜːfɪs/ or /'sɝːfəs/), not "sur-face" (/'sɝːfeɪs/)?Always reminds me of a person I knew who pronounced bicycles as "bi-cycles" (/'bɪsaɪkəl/), not /'baɪsɪkl̩/.