I'm a f*ing idiot! - Page 1
Forum section: electronics / general

author: blueskull
author_rank: Unknown
timestamp: July 09, 2016, 05:27:53 pm
content: I screwed up a schematic symbol of an FPGA by swapping its VCC and VPP (adjacent)... It took me 13 hours to realize it with attempts using 2 different programming cables and wasted 4 chips and an eval kit.Now the chip programs and works fine. I'm glad my code works at the first attempt, but the PCB design has really no excuse to be this f*ed up.I've been designing circuits since 8, started PCB layout at 12, and I've been coding for equally long time. Yet I still make such fundamental errors.Did you ever do such stupid things? How did you overcome it?

author: TiN
author_rank: Super Contributor
timestamp: July 09, 2016, 05:38:30 pm
content: Check and triple-check everything, especially "ofcourse it's correct, that's basics!" things. Even yet even then such things always happen. Sometimes it's just two pins incorrectly swapped, other times it's typo in signal name in schematics passed thru layout and rendering 12 layer PCB with routing on inner layers a bust... no matter how much you know, entropy of chaos prevails...

author: ez24
author_rank: Super Contributor
timestamp: July 09, 2016, 05:53:14 pm
content: My "pins" were 25 of them. I wired a 25 wire parallel connector, mirror backwards and tried to hook it up in the field.

author: ajb
author_rank: Super Contributor
timestamp: July 09, 2016, 06:45:33 pm
content: Most recently, ATSAMD21... all of the power pairs are Gnd then Vcc, except for the analog power pins, which are Vcc then Gnd.Mistakes happen, even stupid ones--that's what prototypes are for. If nothing else, mistakes like this are good opportunities to practice your rework and board bodging skills.

author: dmills
author_rank: Super Contributor
timestamp: July 09, 2016, 08:36:33 pm
content: SFP Module, got the connector footprint backwards compared to the cage....15V PCB mount power supply brick, failed to spot the 'bottom view' on the datasheet, aaarrrgggh.Shit happens, always expect to do a prototype (Or two) because you will anyway....Regards, Dan.

author: imidis
author_rank: Frequent Contributor
timestamp: July 09, 2016, 09:29:11 pm
content: I think the reality is, we are human. Mistakes happen. I also believe, once we are at a point where usually nothing goes wrong, it really throws us of and we forget to check some of the more basic things.

author: David Hess
author_rank: Super Contributor
timestamp: July 09, 2016, 11:25:25 pm
content: Once when laying out a board I swapped Vcc and Gnd between the top and bottom layers. We had to cut two traces and swap them back at one location.

author: Red Squirrel
author_rank: Super Contributor
timestamp: July 09, 2016, 11:34:09 pm
content: I was making a circuit board manually with point to point wire connections (never again!) and the amount of mistakes I kept doing was crazy, because when you're working from the bottom it's reverse, so I was looking at the schematic and then realizing I put the wire on the wrong side of the chip etc. I finally put an indicator on the bottom so I know what is pin 1. Then I'd just count the pins each time.I need to sit down and learn kicad so I can get a PCB made next time. I may even redo this one as a first time exercise.

author: chris_leyson
author_rank: Super Contributor
timestamp: July 09, 2016, 11:57:44 pm
content: Don't worry blueskull, we've all made mistakes, I must have turned off or ignored a design rule check in Orcad PCB for some reason, and then on a production PCB "damn it, it doesn't power up". Luckily it was an easy fix just drill out a pair of vias. It very quickly went up a revision before the next production run. It's easy to loose sight of something because your head is busy concentrating on something else. How many balls can you juggle at once, not literally cos I can't juggle, but you see what I mean, we loose focus on one thing because our heads are focussed somewhere else in the design. Don't worry, learn from our mistakes.

author: TerraHertz
author_rank: Super Contributor
timestamp: July 10, 2016, 12:54:30 am
content: In a commercial work environment it helps to *always* have someone else check your work. Schematics, code, footprints, pcb layouts, etc. Especially if you give them some incentive for finding mistakes.But working on your own, it's almost impossible to gold star (works first time) complex boards.For most of my working career I used a PCB package that had a nice feature - when I thought a PCB design was finished, I could delete the netlist from the design, have the package generate a new netlist from the copper connectivity, then do a comparison between the original netlist and the generated one. This catches several kinds of mistakes, and my boards usually worked first time.Unfortunately that won't catch errors in footprints you made yourself (or provided ones too, sometimes.)

author: Rerouter
author_rank: Super Contributor
timestamp: July 10, 2016, 01:03:53 am
content: Have yet to suffer any pin swaps myself, but a few too many cases of packages or connectors being too close to other packages and the board assemblers complaining to me that it wont work, this is where 3d footprints helps out greatly, (e.g. kicad)Still none of these have killed a product only led to things like filing down the edge of the IDC programming lead,Another one, forgetting to make connections to the ground plane through thermal reliefs, you need some bloody good tools to solder a 144 pin QFN where 15 pins are hard to a ground plane that is stitched to another ground plane on the opposite side right at the pins,Oh and the biggest one of them all, beware mask expansion, make sure your not uncapping your via's because it is too close to the part,

author: gnavigator1007
author_rank: Unknown
timestamp: July 10, 2016, 01:23:42 am
content: Sometimes the ol brains just don't want to work. A few weeks ago I was deep in a repair when I realised I needed to clean my glasses and also charge my phone. I caught myself trying to connect my charger to my glasses. Thought "I'm such an idiot, what the hell was that?". I then immediately catch myself wiping the end of my charger with my shirtMultitasking.

author: tautech
author_rank: Super Contributor
timestamp: July 10, 2016, 02:07:19 am
content: Quote from: gnavigator1007 on July 10, 2016, 01:23:42 amSenior moment.

author: Brumby
author_rank: Unknown
timestamp: July 10, 2016, 03:40:04 am
content: Quote from: gnavigator1007 on July 10, 2016, 01:23:42 amI did that transpose actions thing a couple of days ago. Caught myself doing part one and thought 'idiot' ... then proceeded to perform the 'B' side.I do remember I was sitting at my desk at the time, but for the life of me, I can't remember what they were.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 10, 2016, 03:50:07 am
content: Quote from: TerraHertz on July 10, 2016, 12:54:30 amIt always helps to have other eyes on your work. It is very difficult to see your own mistakes. This principle is so important that it is well worth going to significant lengths to achieve it. Team with other grad students, join clubs so you can share work or whatever it takes.If time isn't too important, and no one else is available to check your work, an alternative is to set the work aside for long enough let it out of the daily thoughts before coming back to it and checking.

author: GreyWoolfe
author_rank: Unknown
timestamp: July 10, 2016, 04:24:09 am
content: Quote from: tautech on July 10, 2016, 02:07:19 amUsed to be senior moments. Now it's all the time.

author: hans
author_rank: Super Contributor
timestamp: July 10, 2016, 06:40:38 am
content: I always double check important work. It's almost a type of OCD if I don't do it; I don't feel at ease sending stuff out the door when I didn't. Yesterday I even sent a letter and thought "hmm, did I double check the address?"However, you are sometimes blind for your own mistakes when the work is still very fresh in your head. It's like writing a paper with the most crap sentences ever possible and not seeing it, because you're still reading your own mind speaking. When you read it back the next day, you think: "Did I write that?" It happens to me regurarly although I'm not diagnosed dyslectic or anything, I guess it just happens. Maybe brains are tired after a long day.What usually helps with me is to leave the project for 1 or 2 days and then come back to review it. Yes that will kill your enthiousiasm or time planning, but it did help me catch lots of fundamental errors. You will always see or memorize certain things to be checked.Indeed, in a work environment I do this as well but also let someone else do it. I also like to hear feedback on my designs and questioning of my thought process.

author: Kjelt
author_rank: Super Contributor
timestamp: July 10, 2016, 08:26:05 am
content: Indeed taking a break go for a walk, bike or something else that clears the mind and then take a second look at the design helps me a lot. But mistakes happen and ordering pcb,s i have changed from ordering a lot the first time to a few to sort problems out. There is always something esp. EMC can be tricky and i often have to add some beads or filter afterwards to not jam the entire fm band with my hf led controller

author: G7PSK
author_rank: Super Contributor
timestamp: July 10, 2016, 09:20:11 am
content: I once hooked up a 900 amp hour battery backwards onto a 3 KW inverter despite having checked every thing 3 times, why pilots of airliners use checklists and call it out to the co pilot, after a while you can get to see what you expect or want to see.

author: SeanB
author_rank: Super Contributor
timestamp: July 10, 2016, 10:36:37 am
content: Years ago hand making some PCB's I accidentally flipped the image, and etched the board. no spare blank PCB, so simply soldered in the components and IC sockets, and took the DIP chips and bent the pins over to the other side and inserted them in the sockets. It did work first time.......

author: diyaudio
author_rank: Frequent Contributor
timestamp: July 10, 2016, 11:45:37 am
content: Quote from: blueskull on July 09, 2016, 05:27:53 pmI made a similar mistake with my first pcb board, however OCD and Altium rules saved me.Question: Your FPGA part, I take it you made a custom schematic symbol + footprint, didn't you setup the schematic PIN I/O rules for power, 0V, signal ect.. by doing this and executing rule checks, one can pickup floating power, shorts rule connections.

author: ajb
author_rank: Super Contributor
timestamp: July 10, 2016, 05:21:04 pm
content: I do wish chip manufacturers would provide better-formatted pin lists. Altium has the ability to paste a list of names and numbers into the pin list, which would be great for MCUs and FPGAs, but I've never found a datasheet that had that information formatted in such a way that I could copy it without losing the structure. Even with the pins are in a tabular format in the datasheet, I guess something about the way the PDF structures the text means they copy and paste as a useless jumbled list. That means you're still stuck transcribing all of that info by hand and risk making subtle mistakes all though the process.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: July 10, 2016, 05:42:36 pm
content: Quote from: ajb on July 10, 2016, 05:21:04 pmIt's because the PDF format has no notion of paragraphs, headings, tables or any other kind of textual semantics like that. It's just "write this string of characters in this font at co-ordinates X,Y". A table is just a collection of strings of text and some line drawing. After all, PDF is based on PostScript, which is a page description language for printing.

author: Gribo
author_rank: Frequent Contributor
timestamp: July 10, 2016, 06:15:02 pm
content: Just got a PCB from production, with MMCX edge mounted connectors. The 3D step file looks fine, however, I forgot to add the cut outs to the mechanical schematics.

author: dmills
author_rank: Super Contributor
timestamp: July 10, 2016, 06:47:18 pm
content: Quote from: ajb on July 10, 2016, 05:21:04 pmTop tip, ignore the datasheet, go for the BSDL file instead, still a pain, but better then trying to pull the tables out of the datasheets.Regards, Dan.

author: KL27x
author_rank: Super Contributor
timestamp: July 11, 2016, 03:14:09 am
content: Never swapped the power pin before, lol. That's rich.I have screwed up other I/O's. Proto, only, not a big run, or anything. I have screwed up a prototype pcb where the only reasonably accessible points to hand-bodge it were still not quite right... so ended up with an extra firmware revision with mixed up pins. Gets to be a headache tracking the different revisions.I remember first time I tried to put components on the bottom layer. I recall figuring out a way to physically install SOT transistors upside down, kinda sorta.Anyone else ever forget to remove ICSP pads from the paste layer?Another time, I had 500 boards made with a RA 0603 LED. I used the footprint and lead placements out of the datasheet, marked the cathode AND the direction the lens shoudl face on the soldermask and placement layers, and got them assembled.... all with the LED leads backwards (LED's flipped over). I take part of the responsibility, because apparently, the LEDs can technically be used the way I had it, but out of the cut tape a PnP machine would not be able to do it that way... and the footprint was basically symmetrical. I should have ordered some parts and examined how they came in the cut strip. The company hand-flipped and reworked them all, no charge, because I had marked them correctly in my Gerbers, but I feel like I could have caught that, myself, with some more experience/foresight, and routed the traces so that each LED didn't need to be flipped over by hand.

author: tszaboo
author_rank: Super Contributor
timestamp: July 11, 2016, 08:36:05 am
content: Dont worry, I managed to design a voltage follower opamp with the positive as the feedback. When the boards did not work, and I realized what I've done, I felt stupid. But I was following an application note, so I checked that one also. Guess what? It was bad there also. So I wrote an email to the author, so she can feel stupid also.You have almost 0% chance of connecting the + and the - wires correctly.

author: Philfreeze
author_rank: Regular Contributor
timestamp: July 11, 2016, 12:56:12 pm
content: Quote from: ajb on July 10, 2016, 05:21:04 pmSometimes it works if you first convert the pdf page into an xlsx or docx (or something else) with a tool likehttps://www.freepdfconvert.comJust 'print' the pages with the IO descriptions with pdfCreator or something similar and then feed the pdf into one of this online converters.

author: FrankD
author_rank: Contributor
timestamp: July 11, 2016, 01:01:24 pm
content: Rule #1Never fix Friday's mistakes on a Monday.

author: tatus1969
author_rank: Super Contributor
timestamp: July 11, 2016, 01:05:57 pm
content: in my last company I had a contest of having the first "first time right". Noone made it. Closest to it was me swapping A-C of an ethernet jack LED, but that was a design with 95% reuse of existing components, plus an ethernet PHY and that said jack.I use to compare this with software programming. Type a 1000 lines of code, inspect and reinspect it, then compile. Anyone had zero errors and code doing exactly what you wanted?

author: ajb
author_rank: Super Contributor
timestamp: July 11, 2016, 03:38:56 pm
content: Quote from: dmills on July 10, 2016, 06:47:18 pmI haven't had much luck finding readily-available BSDL files for MCUs for the MCUs I've used (I don't deal much with FPGAs). By the time you bug a sales rep or FAE for it and finally get a response, it hardly seems worth the trouble for anything less than 100 pins. Honestly I'd be happy with a CSV-formatted listing in the datasheet.

author: Neilm
author_rank: Super Contributor
timestamp: July 11, 2016, 06:00:12 pm
content: Mark it up as a learning experience and move on.that being said, it seems every time I design a window comparator I manage to mess it up - correct in LTSpice, wrong when it gets to the PCB.