Prototyping Circuit - Page 1
Forum section: electronics / beginners

author: brokensegue
author_rank: Contributor
timestamp: November 08, 2021, 10:46:12 pm
content: So I'm working on a circuit design where the plan is to eventually order a PCB and solder it together. I don't want to order a PCB if the circuit design isn't right but I'm unsure how to verify it without doing so. Some of components I'm planning on using aren't available in through-hole. What do more skilled people do here? Are they just confident enough to jump straight to a PCB? Do people use surface mount breakout boards for testing? What about components with weird footprints? just jankily solder leads to the pads?I'm also thinking maybe I should have someone look at my PCB to check it over (I'm teaching myself and I'm definitely making errors). I've heard someone discuss hiring people on fiverr to look over the design? Seems overkill to pay $50 for just a hobbyist board though.Thanks

author: tggzzz
author_rank: Super Contributor
timestamp: November 08, 2021, 10:56:14 pm
content: Here's a variety of techniques, with comments:https://entertaininghacks.wordpress.com/2020/07/22/prototyping-circuits-easy-cheap-fast-reliable-techniques/

author: jpanhalt
author_rank: Super Contributor
timestamp: November 08, 2021, 10:58:16 pm
content: 1) Without seeing your circuit, it is hard to advise specifically.2) Many SMD components, e.g, 1206, can be soldered between pads on common 0.1" pitch perfboard pads.3) There are SMD to TH adapters for IC's. SMD to DIP is very common.

author: ataradov
author_rank: Super Contributor
timestamp: November 08, 2021, 11:01:46 pm
content: Do your best to make sure that the design is right, order PCBs. If something is not right, treat the PCBs as a prototyping board, make bodges as needed, respin the PCB. Once you get better at this, most of the time will work with minimal changes from the first try.You can also ask here for a review, plenty of people do, plenty of people get good feedback. Just post images of your schematics and layout, not just CAD files.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 08, 2021, 11:49:54 pm
content: Some of the classic ways to prototype without a designed PCBFor SMD, prototyping without a designed PCB can be trickier if not impossible in case of very small footprints or BGA chips. That's where devboards/demoboards/modules come into play.What would be a typical prototype in your case? Give an example of a circuit you want to try.

author: james_s
author_rank: Super Contributor
timestamp: November 09, 2021, 12:10:00 am
content: It's so cheap to have PCBs made these days, occasionally I make a breakout board or a simple evaluation board for some part I'm thinking of using. Other times I will hand solder wires to SMT devices, it's possible to deadbug stuff like QFN packages if you have a steady hand and some fine wire.

author: iroc86
author_rank: Regular Contributor
timestamp: November 09, 2021, 03:06:21 am
content: As others have said, making a couple iterations of PCBs is pretty cheap, but it does require board design, layout, and waiting. Depending on the complexity of your circuit, it may be easiest to build a prototype using perfboard or point-to-point wiring. I would avoid relying on solderless breadboards to confirm a design for anything but basic "seat-of-the-pants" verification and testing, or perhaps if the circuit is so simple and obvious that you know it's going to work.You can produce your own adapter boards for weird footprints and other special applications. Sometimes you can find these for common packages (look at Adafruit, SparkFun, or Chip Quik). Other times, it's just easier to do it yourself, say if you need a test point loop or some other kind of feature.You mentioned making errors during the design process--most EDA programs will perform basic design rule checks based on input parameters, and they'll also tell you if traces are disconnected or nets are shorted. You can also use simulation software, like LTspice, to prove out a concept. It's not foolproof, but if you're going straight to PCBs, it can provide some extra reassurance that you've done your homework.

author: brokensegue
author_rank: Contributor
timestamp: November 09, 2021, 03:39:11 am
content: So, yeah it seems like I should maybe buy some breakout boards. I've tried using perfboard before but I had a lot of trouble with it and rats nest wiring or dead bug soldering looks harder.I would use LTSpice or equivalent but I'm unsure how to go about doing that. Is there open source software? Or a tutorial?The project I'm working on is a clock that displays the time using flipdots with a microcontroller. I can do software/micros and I think I know how to wire up logic ICs or regulators (i.e. I can mostly copy schematics from PDFs) but anything that, for example, uses just a bare transistor I'm pretty lost at.Maybe when I'm a little further along I'll post a schematic here and ask for some help directly with that but I want to at least take a shot at debugging it myself first.Thanks for the suggestions.

author: ataradov
author_rank: Super Contributor
timestamp: November 09, 2021, 04:08:52 am
content: Quote from: brokensegue on November 09, 2021, 03:39:11 amIf your circuit includes more than a dozen components, and especially stuff in QFN/QFP, making a custom PCB is really the best approach.If you are not sure in the design, then include extra footprints for potential modifications. But there must be things you know for sure, like power supply stuff, inputs/outputs.Quote from: brokensegue on November 09, 2021, 03:39:11 amJust Use LTSpice itself. It is not open, but it is free and it is good.Quote from: brokensegue on November 09, 2021, 03:39:11 amIn that case LTSpice would be useful to test minor sub-circuits. Do not simulate the whole project.

author: james_s
author_rank: Super Contributor
timestamp: November 09, 2021, 05:46:09 am
content: Dead bug is really not hard, at least not for simple stuff. You don't necessarily have to prototype the entire circuit though, just the part you aren't sure about.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 09, 2021, 08:23:18 am
content: Quote from: brokensegue on November 09, 2021, 03:39:11 amFor this project I don't think simulation would help much. Since you are OK with the software and standard parts like MCU and voltage regulators, then maybe leave that aside and start with controlling a flip dot. I never used one, but since they are electromagnetic devices, I guess they should be controlled by a relay coil, or maybe by a small motor.- First step would be to look for the flipdots datasheet, to learn how much voltage/current they need, and what control signals do they have.- Then, maybe find a typical wiring/schematic in the flipdot's datasheet, or maybe a schematic online from somebody else's flipdots.Once you know that, experiment with a single element, to be sure you can control that. You can put a pic of hand drawn schematic (only the control part, the microcontroller part is irrelevant for now) and a datasheet to the flipdot model you have. That will minimize possible errors in the control schematic of a flipdot, like for example forgetting the protection diode. At first you can use a ready made power supply.Once you have a reliable way to control a single flipdot, and nothing fails or heats, then you go further and multiply/multiplex the control, calculate the total needed current, etc.It is normal for a PCB design to have a few iterations, so don't worry if later you'll discover some problems when more than one flipdot control sit together on the same board.At first you can make the design modular- a power supply module (use a ready made one at first)- a microcontroller board (use a ready made one at first)- the flipdots control board (here you made your own, maybe look for ready made ones, most probably others had to do the same steps like you are doing now, maybe there is a design already)I made once a clock with a big display, it was made with incandescent lightbulbs and meant to work outside. The major problems were the wirings, and the weather. Shield your electronics against direct sunlight, snow carried by wind, etc. and use a dedicated heater for the winter (a simple lightbulb inside the box can be enough), and forced air for cooling it in the summer (some fans). It all depends of the end location of the clock. If it's for indoors usage it is much easier.If it's very big and have to transport the signals over long distances pay attention to ground loops, shielding and possible induced voltage by other billboards or cabling around roofs.

author: tggzzz
author_rank: Super Contributor
timestamp: November 09, 2021, 09:13:44 am
content: Quote from: brokensegue on November 09, 2021, 03:39:11 amRats nest and dead bug are fast and easy, and useful if you don't want to keep the prototype afterwards.LTSpice is free as in beer. There are other spices available if you insist on open source.The usefulness of a spice simulation is critically dependent on the quality of the models. A resistor is an ideal resistor, a capacitor is an ideal capacitor, a voltage source is an ideal voltage source, but for some purposes the parasitic capacitance/resistance/inductance is important. Not all of the models supplied by manufacturers actually model all of a device's behaviour.Nonetheless, for your application spice looks like it will be enlightening. I would pay particular attention to modelling:the electronic behaviour of the flipdot actuatorthe power supply, inserting series inductance (1nH per mm of wire) and series resistance

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 09, 2021, 09:25:23 am
content: Good advice here, I think.Break it down into the smaller tasks that make the whole.If ur using a microcontroller you can get the software right on an arduino first fine, just wire it up to your prototyping stuff, whatever it ends up being, if you use the arduino you will get it done 1 million times quicker than if you were doing things from scratch. its true for everyone.

author: iroc86
author_rank: Regular Contributor
timestamp: November 09, 2021, 03:01:00 pm
content: You also mentioned about a digital logic aspect to your project, so if you're still interested in simulation tools, it might be worth checking out something likeLogisimor its newer fork,Logisim Evolution. It'd be another learning curve, but you could experiment with discrete logic and nail down a design before you started building a board. You'd still need to transfer the simulation schematic to a circuit schematic, but it might be useful to verify your digital design in a fundamental sense.