Proper Decoupling Capacitors

July 12, 2023 by Al Williams 37 Comments

If you’ve been building circuits for any length of time, you probably know you need decoupling capacitors to keep your circuits stable. But even though it’s a favorite technique of ours, just scattering some around your PCB and hoping for the best isn’t necessarily the best approach. If you want to dig deeper into the why and how of decoupling, check out [Stephen Fleeman’s] post on the topic.

It is easy to think of capacitors as open circuits at DC and short circuits at high frequencies, shunting noise to ground. But the truth is more complex than that. Stray resistance and inductance mean that your simple decoupling capacitor will have a resonant frequency. This limits the high frequency protection so you often see multiple values used in parallel to respond to different frequencies.

Because the stray resistance and inductance plays a part, you may want to use fatter traces — less resistance — and shorter runs for less inductance. Of course, you can also use power and ground planes on the PCB as a form of decoupling. At the end of the post, [Stephen] talks a little about the importance of digital and analog ground that interact in a specific way.

If you want to do some empirical testing, you can build a test rig and do the work. Or check with [Bil Herd] about PCB inductance.

Hack Club Grants Encourage Open Source PCB Designs By Teens

June 15, 2023 by Joseph Long 6 Comments

[Hack Club] is a nonprofit network of coder and maker clubs for teenage high school students around the world. With an impressive reach boasting clubs in about 400 schools, they serve approximately 10,000 students. Their OnBoard program asserts, “Circuit boards are magical. You design one, we’ll print it!”

Any teenage high school student can apply for a [Hack Club] OnBoard Grant to have their Printed Circuit Board design fabricated into real hardware. The process starts by designing a PCB using any tool that can generate Gerber files. The student then publishes their design on GitHub and submits the Gerber files to a PCB manufacturer.

A screenshot from the board house showing the completed design upload and production cost is the main requirement of the grant application. If approved, the grant provides up to $100 to cover PCB manufacturing costs.

OnBoard encourages collaboration, community, and friends. Designers can share their projects and progress with [Hack Club] teens around the world. Those who are working on, or have completed, their own circuit board designs can share support and encouragement with their peers.

Example hardware projects from [Hack Club] include Sprig, an open-source handheld game console based on the Raspberry Pi Pico microcontroller. Teen makers can explore the example OnBoard projects and then it’s… three, two, one, go!

Building Circuits Flexibly

May 23, 2023 by Al Williams 20 Comments

You think of breadboards as being a flexible way to build things — one can easily add components and wires and also rip them up. But MIT researchers want to introduce an actual flexible breadboard called FlexBoard. The system is like a traditional breadboard, but it is literally flexible. If you want to affix your prototype to a glove or a ball, good luck with a traditional breadboard. FlexBoard makes it easy. You can see a short video below and a second video presentation about the system, also.

The breadboard uses a plastic living hinge arrangement and otherwise looks more or less like a conventional breadboard. We can think of about a dozen projects this would make easier.

What’s more, it doesn’t seem like it would be that hard to fabricate using a 3D printer and some sacrificial breadboards. The paper reveals that the structures were printed on an Ender 3 using ePLA and a flexible vinyl or nylon filament. Want to try it yourself? You can!

We know what we will be printing this weekend. If you make any cool prototypes with this, be sure to let us know. Sometimes we breadboard virtually. Our favorite breadboards, though, have more than just the breadboard on them.

Continue reading “Building Circuits Flexibly” →

Photoplotting PCBs With A 3D Printer

April 7, 2023 by Al Williams 23 Comments

Do you ever wonder why your PCB maker uses Gerber files? It doesn’t have to do with baby food. Gerber was the company that introduced photoplotting. Early machines used a xenon bulb to project shapes from an aperture to plot on a piece of film. You can then use that film for photolithography which has a lot of uses, including making printed circuit boards. [Wil Straver] decided to make his own photoplotter using a 3D printer in two dimensions and a UV LED. You can see the results in the video below.

A small 3D printed assembly holds a circuit board, the LED, and a magnet to hold it all to the 3D printer. Of course, an LED is a big large for a PCB trace, so he creates a 0.3 mm aperture by printing a mold and using it to cast epoxy to make the part that contacts the PCB film.

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Printing Antennas On Circuit Boards

April 6, 2023 by Bryan Cockfield 19 Comments

Yagi-Uda antennas, or simply “Yagis”, are directional antennas that focus radio waves to increase gain, meaning that the radio waves can travel further in that direction for a given transmitter power. Anyone might recognize an old TV antenna on a roof that uses this type of antenna, but they can be used to increase the gain of an antenna at any frequency. This one is designed to operate within the frequencies allotted to WiFi and as a result is so small that the entire antenna can be printed directly on a PCB.

The antenna consists of what is effectively a dipole antenna, sandwiched in between a reflector and three directors. The reflector and directors are passive elements in that they interact with the radio wave to focus it in a specific direction, but the only thing actually powered is the dipole in the middle. It looks almost like a short circuit at first but thanks to the high frequencies involved in this band, will still function like any other dipole antenna would. [IMSAI Guy], who created the video linked above which goes over these details also analyzed the performance of this antenna and found it to be fairly impressive as a WiFi antenna, but he did make a few changes to the board for some other minor improvements in performance.

The creator of these antennas, [WA5VJB] aka [Kent Britain] is an antenna builder based in Texas who has developed a few unique styles of antennas produced in non-traditional ways. Besides this small Yagi, there are other microwave antennas available for direction-finding, some wide-band antennas, and log-periodic antennas that look similar to Yagi antennas but are fundamentally different designs. But if you’re looking to simply extend your home’s WiFi range you might not need any of these, as Yagi antennas for home routers can be a lot simpler than you ever imagined.

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Picture of the PCB with the text inside the copper pads

Silkscreen Busy? Put Labels Inside Pads

April 4, 2023 by Arya Voronova 21 Comments

When making a PCB informative and self-documenting, there’s often just not enough space to silkscreen all the labels you want, and slowly but surely, you collect a set of tricks: using different through-hole pad shapes to denote ground or power pins, standardized pinouts for connectors, your own signal name shortening notations, and so on.

What if you have some large-ish signal pads on your board, and having the signal names on silkscreen just isn’t good enough? In this case, here’s a new trick for your toolkit: [Christoph] from [MakerProbe] shows us how he puts text directly inside the copper pads.

What you need is a set of Gerber files and a Python script. Technically, this ought to work with any PCB EDA, with [Christoph] using KiCad. You need to put the to-be-subtracted signal names on their very own layer, export Gerber files without features like aperture macros, then run the script. You’ll get a new copper layer as a result, it’s that simple. We also get a set of tips on what kinds of pads suit best and how to prepare them — and fancy-looking real-life examples. You get higher resolution than for on-silkscreen text, solderability isn’t impacted, and the labels are even visible after desoldering wires from the pads. What’s not to like?

Over on Twitter, [Makerprobe] have been doing things like 0201 tombstoning and BGA yield research – we say they’re worth a follow if you’d like to see someone pushing PCB boundaries! Innovative PCB design methods and tricks have a special spot in our hearts, what’s with things like this Tux-emblazoned desktop motherboard that’s also a guide on PCB aesthetics, and there’s a whole lot more you can do to make your PCBs pretty while preserving and even improving functionality. From turning rigid PCBs flexible to hiding components inside a PCB stack, there’s plenty of opportunities that we are yet to extract out of PCB world, and it’s lovely to see one more technique we can make use of.

Continue reading “Silkscreen Busy? Put Labels Inside Pads” →

A bench setup with a spectrum analyzer and a PCB under test

Clever Test Rig Clarifies Capacitor Rules-of-Thumb

March 30, 2023 by Robin Kearey 5 Comments

If you’ve done any amount of electronic design work, you’ll be familiar with the need for decoupling capacitors. Sometimes a chip’s datasheet will tell you exactly what kind of caps to place where, but quite often you’ll have to rely on experience and rules of thumb. For example, you might have heard that you should put 100 µF across the power supply pins and 100 nF close to each chip. But how close is “close”? And can that bigger cap really sit anywhere? [James Wilson] has been doing research to get some firm answers to those questions, and wrote down his findings in a fascinating blog post.

A PCB used to measure the effect of capacitor placement — The test board has two-layer and four-layer sections. The inter-layer capacitance greatly affects the PDN’s performance in each case.

[James] designed a set of circuit boards that enabled him to place different types of capacitors at various distances along a set of PCB traces. By measuring the impedance of such a power distribution network (PDN) across frequency, he could then calculate its performance under different circumstances.

The ideal tool for those measurements would have been a vector network analyzer (VNA), but because [James] didn’t have such an instrument, he made a slightly simpler setup using a spectrum analyzer with a tracking generator. This can only measure the impedance’s magnitude, without any phase information, but that should be good enough for basic PDN characterization.

The results of [James]’s tests are pretty interesting, if not too surprising. For example, those 100 nF capacitors really ought to be placed within 10 mm of your chip if it’s operating at 100 MHz, but you can get away with even 10 cm if no signals go much above 1 MHz. A bulk 100 µF cap can be placed at 10 cm without much penalty in either case. Combining several capacitors of increasing size to get a low impedance across frequency is a good idea in principle, but you need to design the network carefully to avoid resonances between the various components. This is where a not-too-low equivalent series resistance (ESR) is actually a good thing, because it helps to dampen those resonances.

Overall, [James]’s blog post is a good primer on the topic, and gives a bit of much-needed context to those rules of thumb. If you want to dive deeper into the details of PDN design or the inductance of PCB traces, our own [Bil Herd] has made some excellent videos on those topics.