V-Cut Vias Test Your Whole Panel At Once

October 4, 2024 by Arya Voronova 9 Comments

We might consider PCB panels as simply an intermediate step towards getting your PCBs manufactured on the scale of hundreds. This is due to, typically, an inability to run traces beyond your board – and most panel generators don’t give you the option, either. However, if you go for hand-crafted panels or modify a KiKit-created panel, you can easily add extra elements – for instance, why not add vias in the V-Cut path to preserve electrical connectivity between your boards?

[Adam Gulyas] went out and tried just that, and it’s a wonderfully viable method. He shows us how to calculate the via size to be just right given V-Cut and drilling tolerances, and then demonstrates design of an example board with discrete component LED blinkers you can power off a coin cell. The panel gets sent off to be manufactured and assembled, but don’t break the boards apart just yet — connect power to the two through-hole testpoints on the frame, and watch your panel light up all at once.

It’s a flashy demonstration – even more so once you put light-diffusing spheres on top of the domes. You could always do such a trick with mousebites, but you risk having the tracks tear off the board, and, V-Cuts are no doubt the cleanest way to panelize – no edge cleaning is required after breaking the boards apart. Want to learn about panel design? We’ve written and featured multiple guides for you over the years.

3D Print A Stenciling Frame For Your PCB

October 3, 2024 by Arya Voronova 14 Comments

For many a hacker, stenciling a board for the first time is a game-changing experience – the solder joints you get, sure do give your PCB the aura of a mass-manufactured device. Now, you might not get a perfect print – and neither did [Atul R]. Not to worry, because if you have a 3D printer handy, he’s showing you how to design a 3D-printed frame using Blender and TinkerCAD, making your solder paste print well even if you’re trying to rest a giant stencil on top of a tiny board.

[Atul]’s situation was non-characteristic – the project is a 2mm thick PCB designed to plug right into a USB port, so the usual trick of using some scrap PCBs wouldn’t work, and using a 3D-printed frame turned out to be key. To get it done, he exported a .wrl from KiCad, processed it in Blender, and then designed a frame with help of TinkerCAD. These techniques, no doubt, will translate into your CAD of choice – especially if you go with .step export instead of .wrl.

This kind of frame design will get you far, especially for boards where the more common techniques fail – say, if you need to assemble a double-sided board and one side is already populated. Don’t have a stencil? You could surely make a 3D printed stencil, too, both for KiCad boards and for random Gerber files. Oh, and don’t forget this 3D-printable stencil alignment jig, while you’re at it – looks like it ought to save you quite a bit of trouble.

Supercon 2023: Thea Flowers Renders KiCad Projects On The Web

October 1, 2024 by Arya Voronova 8 Comments

Last year’s Supercon, we’ve had the pleasure of hosting Thea [Stargirl] Flowers, who told us about her KiCanvas project, with its trials, its tribulations, and its triumphs. KiCanvas brings interactive display of KiCad boards and schematics into your browser, letting you embed your PCB’s information right into your blog post or online documentation.

Give the KiCanvas plugin a URL to your KiCad file, and it will render your file in the browser, fully on the fly. There’s no .jpg to update and re-upload, no jobs to re-run each time you find a mistake and update your board – your files are always up to date, and your audience is always able to check it out without launching KiCad.

Images are an intuitive representation for schematics and PCB files, but they’re letting hackers down massively. Thea’s KiCanvas project is about making our KiCad projects all that more accessible to newcomers, and it’s succeeded – nowadays, you can encounter KiCanvas schematic embeds in the wild on various hackers’ blogs. The Typescript code didn’t write itself, and neither was it easy – she’s brought a fair few war stories to the DesignLab stage.

A hacker’s passion to share can move mountains. Thea’s task was a formidable one, too – KiCad is a monumental project with a decades-long history. There are quite respectable reasons for someone to move this particular mountain – helping you share your projects quickly but extensively, and letting people learn about your projects without breaking a sweat.

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Where Do You Connect The Shield?

September 13, 2024 by Arya Voronova 24 Comments

When it comes to polarizing and confusing questions in electronics, wiring up shields is on the top-10 list when sorted by popularity. It’s a question most of us need to figure out at some point – when you place a USB socket symbol on your schematic, where do you wire up the SHIELD and MP pins?

Once you look it up, you will find Eevblog forum threads with dozens of conflicting replies, Stackexchange posts with seven different responses plus a few downvoted ones, none of them accepted, and if you try to consult the literature, the answer will invariably be “it depends”.

I’m not a connector-ground expert, I just do a fair bit of both reading and hacking. Still, I’ve been trying to figure out this debate, for a couple years now, re-reading the forum posts each time I started a new schematic with a yet-unfamiliar connector. Now, of course, coming to this question with my own bias, here’s a summary you can fall back on.

Consumer Ports

Putting HDMI on your board? First of all, good luck. Then, consider – do you have a reason to avoid connecting the shield? If not, certainly connect the shield to ground, use jumpers if that’s what makes you comfortable, though there’s a good argument that you should just connect directly, too. The reason is simple: a fair few HDMI cables omit GND pin connections, fully relying on the shield for return currents. When your HDMI connection misfires, you don’t want to be debugging your HDMI transmitter settings when the actual No Signal problem, as unintuitive as it sounds, will be simply your shield not being grounded – like BeagleBone and Odroid didn’t in the early days. By the way, is a DVI-D to HDMI adapter not working for you? Well, it might just be that it’s built in a cheap way and doesn’t connect the shields of the two sockets together – which is fixable.

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Simple PCB Agitator Gets The Job Done

September 13, 2024 by Lewin Day 17 Comments

These days, PCB fab houses are just about everywhere, and you can’t go buy a taco without walking past eight of them. Still, some out there still like to etch their PCBs at home. If that sounds like you, you might see some value in [Chris Borge]’s PCB agitator.

The design mostly relies on 3D printed parts, including the main body. It has a heavy base which is filled with concrete to keep it nicely weighed down on the table. A table for holding a PCB and fluid tank is then installed on top, via a bearing which allows it to pivot in one axis. An Arduino Nano commands the agitation of the table top, and hence the PCB etching tank, with a servo used to actually shift the table back and forth.

It’s a simple design — far simpler than some of the advanced coffee-making hardware we’ve seen recently. Regardless, it gets the job done, and done well! In testing, it accelerated [Chris]’s etching jobs significantly, we’re talking hours here. Meanwhile, if you don’t have a 3D printer on hand, you could always try building one out of junk instead!

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Hands hold a set of white, 3D printed connectors above a wooden table. They look like a cross between a ballpoint pen tip and a spider. The shorter one on the right has yellow, green, black, purple, and white wires coming out the top.

SWD Interface Simplifies Debugging

August 28, 2024 by Navarre Bartz 29 Comments

The proliferation of microcontrollers has made it easier than ever to add some smarts to a project, but sometimes there just isn’t enough space for headers on a board, or you feel a little silly soldering something that will get used to flash a program then languish inside your build. [Dima] wanted to make his boards easier to flash, and developed a PCB footprint and flashing tool pair that makes use of the mounting holes on his boards.

While some debugging tools might use a clamp or tape, [Dima] discovered that using sprung pins only on one side of the connector wedged his fixed locator pin (originally a 1 mm drill bit) into the hole removing the need for any other holding mechanism.

His original prototype worked so well that it took him some time to get back around to making a more reproducible design that didn’t involve fine soldering and superglue. After enlarging the contact pads and several iterations of 3D printing, he developed an interface connector that uses standard jumper wires and a steel rod to provide a sturdy and reliable connection for flashing boards with the corresponding footprint. He’s currently a little disappointed with the overall size of the connector though, and is soliciting feedback on how to make it smaller.

While [Dima]’s MCU of choice is the STM32, but this design should be applicable to any other microcontrollers using a five wire system, or you could take one off for USB. Having trouble finding the SWD points on an existing device? Try this method.

Thanks to [DjBiohazard] for the tip!

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A Simple Guide To RF PCB Design

August 23, 2024 by Dave Rowntree 9 Comments

[Hans Rosenberg] knows a thing or two about RF PCB design and has provided a ~~three-part~~ four-part video demonstration of some solid rules of thumb. We will cover the first part here and leave the other two for the more interested readers!

The design process begins with a schematic diagram, assuming ideal conductors. Advanced software tools can extract the resistive, inductive, and capacitive elements of the physical wiring to create a parasitic model that can be compared to the desired schematic. The RF designer’s task is to optimize the layout to minimize differences and achieve the best performance to meet the design goals. However, what do you do when you don’t have access to such software?

[Hans] explains that at low frequencies, return current flows through all paths, with the lowest resistance path taking most of the current. At higher frequencies, the lowest inductance path carries all the current. In real designs, a ground plane is used instead of an explicit return trace for the lowest possible impedance.

You really wouldn’t design an RF circuit like this.

[Hans] shows the effect of interrupting the signal return path on a physical test PCB. The result is pretty bad, with the current forced to detour around the hole in the ground plane. A nanoVNA shows a -20 dB drop at 4 GHz, where the ground plane has effectively become an antenna. Energy will be radiated out, causing signal loss, but worse, it will create an EMC hazard with an unintended transmission.

Additionally, this creates an EMC susceptibility, making the situation worse. Placing a solder blob to bridge the gap directly under the signal trace is all that’s required to make it a continuous straight path again, and the performance is restored.

Floating planes are also an issue in RF designs, causing signal resonance and losses. One solution is to pull back the planes near the signal or stitch them to the ground plane with vias placed closely on either side of the signal trace. However, such stitching may slightly affect transmission line impedance and require tweaking the design a little. The next two parts of the series expand on this, hammering home the importance of good ground plane design. These are definitely worth a watch!

PCB design is as much art as science, and we’ve discussed this subject a lot. Here’s our simple guide to rocking RF PCB designs. There’s also a lot of devil in that detail, for example when understanding edge-launch SMA connectors.

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