PCB Layout: How am I doing? - Page 1
Forum section: electronics / projects

author: DrMag
author_rank: Regular Contributor
timestamp: January 06, 2015, 11:32:15 pm
content: I'm looking for some helpful (and honest) critique. While there are lots of places on the web to learn how to use PCB layout software, there isn't much by way of do's and don'ts of layout technique, so much of what I've learned has been trial and error. I thought I'd ask for some guidance on what I might do better. This layout was done in KiCAD, which I've not used before, and I'm finding the software has some frustrating quirks I had to work around.This board is for a Raspberry Pi A+/B+ (ultimately the start of a telemetry system) that adds a backup battery with automatic switching and shutdown if the main power drops out. The backup battery is charged when plugged into main power. It also adds a real time clock for remote use, where it won't have access to the internet. The EEPROM is for ID purposes. The switch in the lower left corner lets you manually cycle between power modes, and has built-in LEDs to use for indicating the current state of the system. The MSP430 monitors the power lines and handles the power switching. I've added a couple of LEDs to one of its GPIOs for future use/information.The top fill plane is ground, and the fill planes on the bottom are as follows (VBus being the main power line, Vcc the 5V on the RPi):+------------------+| Vcc | GND |+--------+--------+| VBus |+------------------+| GND |+------------------+Schematic PDF:http://share.mspsci.com/data/public/24c0b2.phpSVG Files of layers:http://share.mspsci.com/data/public/17f69d.phpGerber Files:http://share.mspsci.com/data/public/67f3fa.phpAny thoughts or suggestions/corrections?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 07, 2015, 01:41:19 am
content: I'll start with the schematic.1) Nicely done overall. Everything's lined up and clear, good use of labels.2) I note that some text overlaps lines, ex U1A is over the ground signal. Etc, several locations.3) There is no junction dot at the output of the U1 op-amps. Are the nets as you want? Maybe move the junction away by one grid point so the dot appears?4) U3, wire drawn through body of U3. Pin 5 to 14 I guess.5) Dotted lines for separating functions, not really needed, it's obvious by itself, just adds visual noise.6) Add decoupling caps to U1 and U5.7) Odd symbol for P2, what is it? Is that the pogo pin connector that's just a bunch of pads on the PCB? Either way make it horizontal on the schematic.VIII) Does the USB connector need ESD protection even if it's just bringing power?I needed Roman numerals for the last one since it becomes a smiley...

author: DrMag
author_rank: Regular Contributor
timestamp: January 07, 2015, 03:52:42 pm
content: Those are helpful comments, thanks! Yes, P2 is a pin connector for flashing the MCU (fromhere). I'm not aware of any standard symbol for such a thing, so I made one up myself, hence the odd symbol.Any chance someone has taken a look at the layout itself?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 09, 2015, 03:59:19 pm
content: I started a list in the browser but thanks to windows update I lost it...You still need a PCB review?

author: c4757p
author_rank: Super Contributor
timestamp: January 09, 2015, 04:23:32 pm
content: Quote from: Alex Eisenhut on January 07, 2015, 01:41:19 amAttachments and other options -> Don't use smileys. -> 8)

author: DrMag
author_rank: Regular Contributor
timestamp: January 09, 2015, 04:39:23 pm
content: Alex, if you have the time, yes I'd appreciate it! I'm sorry about the list.I read up on ESD protection and decided to add it to the design, as well as putting in a PTC before the 5V rail, so I've redone the whole board, but my posting it was primarily to learn more about layout technique. It's easy to find help on how to use the software, but for whatever reason information on how to actually choose the layout is sparse.