@misk94555 It hasn't changed that much. The main thing that happened some 15-20 years ago was the transition from assembler to C gaining some serious momentum. Then the MISRA C release in 2004 which brought quality up a notch, though back then it wasn't used outside safety-critical firmware I think. I started using it quite early since I worked which such projects.

@misk94555 One of the tricks to writing high quality production firmware is to do that to begin with. As in, don't write some demo/test program which you later refine. Start with production quality code directly. When I started doing that, the final results got so much better.

Because while we pretend otherwise, people always forget remains of old debug code or quick dirty patches and leave those behind. Version control won't help with that either, if you commit the stuff all the time while doing early testing.

Also if you focus on production quality code from the start, you'll start to question the program design early on as well. And the earlier you finds mistake in it, the better. IMO people who speak of "refactoring" aka "rewrite the whole thing from scratch" are those who haven't realized it is better to write the code proper to begin with.

Does anyone have any experience from metal core PCBs? Specifically, how much more expensive are they, typically?

@Lundin [I’ve used modules made with metal core PCB (amplifiers). Haven’t designed or fabricated metal core PCBs myself, yet. ]

PCBway does metal core boards (aluminium and copper). They have an automated quoting system, which can give you an estimate based just on size without the actual layout. You could glean something about relative cost there.

pcbway.com/orderonline.aspx

pcbway.com/pcb_prototype/Metal_core_PCBs.html

[Due to the nature of your business in the end you’ll be ordering the board somewhere in the Free Hi-rel World. PCBway may give you an additional reference point for not a lot of effort. ]

@NickAlexeev Yeah I got curious about it after watching a PCBway video on youtube actually. With an upcoming project we need lots of cooling for various MOSFETs and planned to use some external metal part, but this would be neater mechanics-wise if not too expensive.

A colleague recently did a Power of Ethernet supply thing with massive copper layers to deal with currents and that thing turned really expensive. But I'm guessing there's a price difference between thick signal layers and just having a core that only needs to have good thermal characteristics. Admittedly I don't know much about PCB stack-ups in general :)

Hi!

can someone help me pls

@Pizza What's up?

@NickAlexeev hi

Design a transcoder for converting signed magnitude 4-bit numbers into their equivalent two's complement representation

if you can help me i would really appreciate it

oh wait

no... I don't understand how to do it

@Pizza Let a little MCU do the job? Or does it have to be done in pure "hardware"?

@Lundin i need to do this on paper...

Hmm. Something like... grab the value part not including the sign. If the sign is set, invert the value part and then add +1 to it

yes

Like, if you have the decimal number -123. Take the 123 part = 0x7B. Invert it = 0x84. Add +1 = 0x85 = -123 in two's complement

Except if the two's complement number has to be larger, then it needs to get "sign extended" but inverting the original data will cover that too, given that the original data is the same size as the result.

As for signed magnitude, it is the easiest signed format to understand really. Just a value part and a sign bit.

but shouldnt i use Karnaugh map ?

@NickAlexeev Regarding the "Hi rel world", can you really buy PCBs outside of south east Asia these days? We buy most of ours from South Korea but we do use PCBway too at least for prototypes. There's no PCB vendors left in Europe that's worth the effort.

@Pizza Only if you are implementing this with 74HC logic, a "PLD" or the like. I guess for 1 sign bit + 3 value bits you can draw up a truth table and then K map from there.

ok thanks!

@Lundin Yes. Sometimes I buy PCBs from Sunstone (Oregon, US), BayAreaCircuits (hi-rel and decent tech levels, California, US).

Having said that, this part of the US de facto has been a prefecture of Japan since the 1970s, and a province of China since mid 1990s.

@Lundin Yes there’s a difference between a heavy¹ copper layer on a PCB and a metal core PCB². Heavy copper is created by electroplating additional copper onto copper foil. Then it’s etched, vias are drilled, etc. Metal core, on the other hand, is cut from a sheet of metal.

That technical difference should reflect in price.

¹ More than 2 oz/ft² is heavy copper, afaik.

² Single sided. I don’t know about double sided.

@NickAlexeev When I joined the electronics business around year 2022 we had local PCB manfacturers all over. Mostly for prototyping but still. Like at least one in every small town. Then there was this big one in Norway. They all went bankrupt because they produced low quality boards at a higher price. This company in Norway in particular was horrible, we had to troubleshoot the actual PCBs on regular basis. "Aha there's a short between layer 2 and 3" that kind of BS.

Like, they would send us a panel with 10 boards where they had drawn black 'X' across half of them. "These are bad but we won't charge you for them." I mean wtf...

Ahem. That's around year 2002* I'm not that green :)

@Lundin X-outs in a panel are a normal practice. Were you pushing PCB state of the art [for its time] ? 50% of x-outs sounds too much for run-of-the-mill PCBs.

You can specify "no X-outs" or "no more than n x-outs per panel" when you order boards. But that increases cost, because the fab would have to scrap more panels.

@NickAlexeev To me it just sounds as if the manufacturer has a problem in their process. They apply the whole layer to the panel at once yeah? If there's some manner of thermal issue to make the prepreg stuff do its job or whatever, that's none of my business.

Also even if I would accept X:ed out boards because they are cheaper, then my assembly contractor will in turn charge me more because they have to give each panel some extra love. They tend to prefer smaller panels with fewer boards anyway.

@Lundin My assembly contractor (the PCBA house) abstracts this decision from me because they are the ones ordering the bare PCBs. They know how much extra love costs them, they know the yield and expected number of x-outs, and they can make an economic decision.

@Lundin It depends. There's number of things that can go awry during PCB fabrication. Adhesive and lamination is one of them. Photoresist and etching issues can cause shorts or opens. They didn't tell you what were the particular types of defects in the x-outed boards, did they?