Breadboard layout vs PCB layout  - Page 1
Forum section: electronics / beginners

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 21, 2019, 07:49:39 pm
content: How often do u lay out a PCB just like on the BB ? Some PCBs are nothing like how a BB version would look. Today I'm making something and I should just copy the BB version almost exactly,, it's a linear DC PSU with only BJTs being active. It looks perfectly logical, neat and tidy, and fills the BB more or less.But I'm wondering how a professional, or a CAD program would lay it out. For such low frequency, maybe the whole would be all jammed together in a big maze/knotWhats a good free program that takes a schematic and makes a circuit layout ? I'm using perf.board with the single copper rings. For that matter can LTspice make a layout ?When does it matter the angle of traces/wires, when changing direction ? Lot's of old AM/FM radio's sure didn't care about curved traces, and a big maze/jumble of parts. Are 90deg angles always preferred ? Is that due to the magnetic fields of currents ?

author: Siwastaja
author_rank: Super Contributor
timestamp: June 21, 2019, 07:59:32 pm
content: Such auto layout tool hasn't been made and probably won't be in the near future. The problem is way too complex.Some dedicated layout generators do exist, for example the TI Webench which basically crunches and modifies TI's pre-built power converter layouts to suit the user parameters. IMHO, they are of little value.What comes to your question, depends on circuit. Sometimes it just happens that a certain circuit schematic worksverywell on a breadboard, and if this is the case, the optimal PCB layout would look similar.But, a PCB design gives you so much more freedom, especially if you can afford extra layers. Given a fixed circuit complexity, the more you have layers to work with, the easier everything gets.Trace angles are electrically irrelevant unless we are talking about really high-speed radio frequency stuff.On the other hand, good reference planes (contiguous ground pours, preferably at least one layer dedicated to ground only) tend to be very important in many different types of circuits (almost anything but the simplest very low-frequency stuff): power converters, seemingly low frequency stuff that still have high edge rates (think about a 8MHz microcontroller), sensitive analog stuff, high-speed digital circuits, or, of course, RF.But a circuit consisting of a connector, series resistor, and an LED wouldn't care about a ground plane.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 21, 2019, 08:04:12 pm
content: With a good voltage regulator one may still have to watch out for trace resistance. Ideally one would also do this on the breadboard, but there one tends to accept a few more compromises - though contacts and resistance are often much worse.Even for a DC supply the regulation loop may still have a loop gain up to the low MHz range. So at some points one may have to keep an eye on the layout. Especially the low output impedance part is sensitive to parasitic inductance.Its rare the the PCB layout will directly follow the bread board. Usually one can do better with part placement.The quality of the auto-router is often still quite marginal, especially with only 1 or 2 layer analog circuits. Very good ones may be wort it ar 4 layers or so for some part. Automatic placement tends to be even worse - though with some KI this could work in the future. At least I have not seen anything useful.

author: cur8xgo
author_rank: Regular Contributor
timestamp: June 21, 2019, 08:09:39 pm
content: Auto-routers can be very powerful tools if setup right. They certainly do exist and are used all the time. They can make sure vast amounts of complex rules are followed and are much cheaper and possibly more reliable (rules wise) than having a person lay out something like a motherboard or some other super complex multilayer PCB.That said, not justified for simple circuits, and you would spend as much time configuring the auto router as you would just doing the layout yourself. Making a layout is a good skillset to build and will pay off in big ways.I have used auto-routers to router very dense, very small, but not that complex PCB's before. Did a great job.

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 21, 2019, 08:44:32 pm
content: I'm making a linear DC adjustable PSU, and the main guts, minus the knobs, will easily fit on a 9x15cm perf.board. And I could have nice straight rails. It uses 3 transformer winding.I also have 9x15cm copper clad board. That would be fun, would there be any real difference to deadbug the thing ? I know for RF yes, but since cost and time don't matter, would it make it an "expensive" and better linear DC adjustable all BJT PSU, if I used copper clad, would it really make it even quieter ? I plan on putting it in a DVD player case.I find on perf.board, it's too easy to pile on the solder. I need to use the trimmed leads as wires/traces way more often and make it much cleaner, and lighter too

author: Nusa
author_rank: Super Contributor
timestamp: June 21, 2019, 08:58:49 pm
content: The answer depends on the quantity you want to produce. If that number is 1, any method that gives you the desired result is a correct method. If it's a very low number, you have to decide where the time and energy trade-off is between hand and machine processes. If it's a large number, then you obviously need to do a proper layout.

author: cur8xgo
author_rank: Regular Contributor
timestamp: June 21, 2019, 10:07:10 pm
content: Quote from: lordvader88 on June 21, 2019, 08:44:32 pmIs this important for some reason?

author: KL27x
author_rank: Super Contributor
timestamp: June 23, 2019, 01:35:03 am
content: When you use PCB software, you should most definitely learn to make the schematic and work from that.The schematic will look exactly the same as the one for the breadboard (which you may or may not have drawn out, yet).First step, is make the schematic. This will include making custom library parts, in many cases. Then start laying out the board. Put the connectors where they have to be. Then sprinkle the components on and start rotating/repositiong them until all those unrouted lines start looking reasoable. Then start routing, ripping up, repositioning/rotating, rerouting. Don't get too involved in placing and positioning traces until it starts to look sensible, compact, without a million vias.There's no reason the PCB should look anything at all like the breadboard when you're done, unless you are working backwards without inputting a schematic in the PCB program and just trying to copy the wires/traces from looking at a breadboard! The PCB can be way smaller.If this is literally a one-off, and you don't care to draw up a schematic... but OTOH, you either don't want to lose your breadboard or the breadboard isn't physically robust enough? I would solder it to a breadboard shaped protoboard.Even after the learning curve is over, and you are proficient at it? It will still take way longer to make a PCB for very simple circuits... esp stuff so simple you don't even want to draw a schematic in the first place. But with more complex circuits, it will actually save you time as well as making it easy to make more than one.

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 23, 2019, 05:18:08 pm
content: Quote from: cur8xgo on June 21, 2019, 10:07:10 pmWell isn't it more similar to having a ground plane ? Or at low frequencies it just doesn't matter ?

author: Siwastaja
author_rank: Super Contributor
timestamp: June 23, 2019, 08:49:25 pm
content: Quote from: lordvader88 on June 23, 2019, 05:18:08 pmIt's most important to look for traces where you have changing currents, and look for the return path (from ground pins to capacitors, for example) this current needs to take. They are not supposed to form long loops. If you can't afford a proper ground plane, you need to pay some attention and do this manually, as optimally as you can.Full ground plane is the easiest way to minimize all loops, since the alternating current automatically takes the optimum path from the EMI perspective (minimal loop, i.e., it goes just below the trace where the current flows). DC (and very low frequencies), on the other hand, automatically take theshortestpath on the ground plane, which is different, but from the DC viewpoint, it's often the optimal as well!

author: Kleinstein
author_rank: Super Contributor
timestamp: June 24, 2019, 06:58:03 am
content: For just quantity 1 and not too high frequency prototype boards with breadboard like stripes can be a good solution. There are strip type boards and with a saw it is reasonably easy to get one separation all across so that the board looks a lot like the breadboard.Dead bug stype is also OK for a low frequency if the circuit is reasonably simple. A ground plane can also be used for DC and is probably good enough for most case, except when going to the volt-nut territory. Than a star ground scheme is more appropriate.

author: Peabody
author_rank: Super Contributor
timestamp: June 24, 2019, 10:22:50 pm
content: They make PC boards already laid out in the same pattern as breadboards. So you wouldn't actually need to have a board made at all.https://www.ebay.com/itm/112951198754I've used these for a number of projects, and they work pretty well. For a quantity of one or two, they are cheap and quick (just take one off the stack). The only real downside is that the rails aren't quite at the same locations as they are on breadboards, so things like breadboard power supply modules don't quite fit. And I end up replacing all the Duponts with 22 gauge jumpers cut to fit so the lie flat, which takes a little time. But I don't have to wait for a shipment from China, and it's pretty easy to change something if needed.