First PCB - General Questions and Schematic check - Page 1
Forum section: electronics / beginners

author: Torch09
author_rank: Newbie
timestamp: January 19, 2022, 04:36:29 pm
content: Hello everyone,After I had always used complete boards for my small projects, I wanted to build my own.This is my first board; I would like to ask some questions which I’m not really sure of and maybe you could look over the circuit to point out if there are errors I made.My plan is to design it with EasyEDA and use the production and assembly service from JLCPCB.The Microcontroller I’m using is a RP2040, because I’ve worked with the Raspi Devices before, and the documentation seems pretty good for beginners (mostly the Hardware Design Guide).There are some components which I changed, because JLCPCB has “Basic Parts” which don’t cost more in the assembly process, for every part which is not a “Basic Part” I need to pay 3€ setup fee.I will only get 5 Boards, which I won’t sell, so this would be getting expensive for this basic test board.I have added my schematic and the BOM to the attachments.The BOM includes the ws2812b and the header, but I’ll solder them myself. JLCPCB doesn’t support two side assembly, so no other chance.I’m currently working on making the PCB, if everything from the schematic looks good, I will add it to the post.Currently the RP2040 is not available on JLCPCB so I thought about replacing it with a STM32F030C8T6 but currently I hope that it gets restocked in the near future.Function:The board should just be a basic test board where I can test some code and with some lighting on the bottom.I’ve added some GPIOs to a Header for future connection to buttons or something along the lines.Questions:USB Protection:I’ve added a ProTek SRV05-4 TVS. I haven’t found circuits with this specific IC to verify my schematic, so I connected it like the Datasheet said. The Schottky on the 5V line is a MDD SS14.Would the USB protection for 5V and Data work this way or is this done another way? I’ve read about littlefuses, but they are sadly not in the JLCPCB Basic Part list.Crystal:I had to use another Crystal, because the one in the Raspi Guide isn’t supported for Assembly. The Crystal I choose is a X322512MSB4SI (12MHz like the one used by raspi). This Crystal has 4 pins of which two are GND, I connected it the same way Raspi does but had to calculate the Capacitors (Crystal CL: 20pf, Cstray=5pf). I used the formular form adafruits blog: “C1, C2 = 2*CL – 2*Cstray”Schematic:Is there something which you would add or remove from the schematic to make it more readable or to comply with any rules? I tried to mimic the schematic design from people who seem to know what they are doing ().General:Would you make something another way or is there anything which would make sense to include in the schematic / design?Datasheets for quick navigation:TVS:https://datasheet.lcsc.com/lcsc/1809192313_ProTek-Devices-SRV05-4-P-T7_C85364.pdfCrystal X322512MSB4SI:https://datasheet.lcsc.com/lcsc/2103291203_Yangxing-Tech-X322512MSB4SI_C9002.pdfRP2040 Hardware Design guide:https://datasheets.raspberrypi.com/rp2040/hardware-design-with-rp2040.pdfW25Q128JVSIQ Flash SPI:https://datasheet.lcsc.com/lcsc/1811142111_Winbond-Elec-W25Q128JVSIQ_C97521.pdfAO3400A MOSFET for 3.3 to 5v:https://datasheet.lcsc.com/lcsc/1811081213_Alpha-&-Omega-Semicon-AO3400A_C20917.pdfThanks in advance for your help!

author: Benta
author_rank: Super Contributor
timestamp: January 19, 2022, 08:40:19 pm
content: Why is the schematic split into x number of single sheets? It's impossible to read without spending 20 times as much time as with a regular schematic.You have no space problems on the sheet. Placing each component on a separate sheet is senseless.I have no other comments, as the design is undecipherable.

author: Torch09
author_rank: Newbie
timestamp: January 19, 2022, 09:10:26 pm
content: First of all, thanks for the comment.The PDF consists of 2 A4 sheets, do you mean to make the sheet bigger (A3+) so the logical blocks fit on one "big page" and not two small ones?I read on Autodesk tips topic to use a standard sheet of paper, which is A4. Is this something like best practice but not used in the real world?Everything on one page like this?:https://github.com/ShawnHymel/rpi-pico-debugger-shoe/blob/master/hardware/rpi-pico-debugger-shoe/rpi-pico-debugger-shoe_schematic.pdf

author: Benta
author_rank: Super Contributor
timestamp: January 19, 2022, 09:21:39 pm
content: Quote from: Torch09 on January 19, 2022, 09:10:26 pmNo.I mean putting all relevant components on one sheet and usingwiresto connect the pins.Placing certain parts, like the power supply, or connectors on a separate sheet can make sense, but needs careful thinking.But your "little boxes, little boxes, made of..." renders it unreadable.Instead of just following a wire, I'm forced to look for labels all over the place, and I'm not even sure if there's a 1:1 correspondence or if I have to look further.I attach an example of a readable schematic.

author: Torch09
author_rank: Newbie
timestamp: January 19, 2022, 09:27:58 pm
content: ok, understood that.Just followed the example from the sheet I linked, but I will make my sheet more readable and update the attachment.Thanks.

author: Benta
author_rank: Super Contributor
timestamp: January 19, 2022, 09:46:35 pm
content: I look forward to itWe all started out sometime.Drawing schematics is an art. The most basic part is: "will other people understand how this works?"The most basic rule is: "main signal flow is from left to right"... just like reading text.For supply voltages: "the most positive voltage is at the top, the most negative at the bottom. Other supply/bias voltages are in between."Labels are for going off-sheet (Input/output/supply or to a different circuit). Otherwise wires/connections/buses should be used.This is what people reading a schematic expect.The schematic you linked to was drawn by someone who misunderstood the concept of "hierachic sheets" completely. Unfortunately, lots of those around.Cheers.

author: Torch09
author_rank: Newbie
timestamp: January 19, 2022, 10:12:08 pm
content: Thank you again for the tips and your time!I'll try to match this as much as I can.This is the first time I'm drawing something like this not just for myself, but posting this on the Internet.Its kind of hard to think how someone, who didn't draw this, would react, but I hope I will get better in this over timeAs this is not even close to my main job, I'll try to read/watch as much as possible but the world around electronics is... well.. kind of bigThanks again, will update it after work tomorrow.

author: Torch09
author_rank: Newbie
timestamp: January 20, 2022, 06:42:17 pm
content: I uploaded the new Schematic and BOM.The files have a "_wire" suffix.I hope this makes it more readable and not too cramped, the labels are removed and replaced by wires and buses. Tried to move the components based on the flow.I tried to split the schematic in parts based on the voltages.

author: Benta
author_rank: Super Contributor
timestamp: January 20, 2022, 08:55:24 pm
content: Looking MUCH better!At least the viewer now has an idea of what the circuit does.How you partition it (in your case according to supply voltage) is your artistic freedom.A couple of questions/comments:1: does the RP2040 really need 11 decoupling capacitors next to it? Or do they actually belong somewhere else?*2: bus entries can be both 45 and -45 degrees, just edit them in KiCAD. They look a bit weird.* if they belong to different ICs, one solution is to place them separately on the schematic. In this case labels are absolutely OK. A text comment above each cap saying where they belong (eg, U1, U3 etc.) will remove a lot of clutter. Important on a schematic is that active signal flow is clear. Power can be kept separate.You're learning fastCheers.

author: Torch09
author_rank: Newbie
timestamp: January 20, 2022, 10:29:14 pm
content: That is nice to hear, thank you!1.Indeed, all the capacitors are for the RP2040, normally there is even one more, but the Hardware Design Guide for the RP2040 didn't include it, so I will do the same.JLCPCB only supports one side assembly, so this will be cramped either way2.I'm currently using EasyEDA as it seemed like this is the easiest on for a beginner, but I read that KiCAD seems like the go to in the Hobby-World, so I think I'll switch too.I'll look for rotate entry and fix the bus entries.Ah, thats nice to know!Thanks again for your time!Feels like I made a step forward to understand how schematics should me drawn