Day: February 25, 2025

Tech In Plain Sight: Magsafe, And How To Roll Your Own

February 25, 2025 by No comments

Apple likes magnets. They started out with magnetic laptop chargers and then graduated to a system that magnetically holds the phone, charges it, and can facilitate communication between the phone and a charger or other device. Even if you are like me and have no Apple devices, you can retrofit other phones to use Magsafe accessories. In fact, with a little work, you can build your own devices. Regardless, the technology is a clever and simple hack, and we are just a little sorry we didn’t think of it.

Terms

Using a magnet to attach a phone isn’t a new idea. But, historically, the phone had either a metal back or an adhesive metal plate attached that would stick to the magnet. This wouldn’t necessarily help with charging, but was perfectly fine for holding the device. The problem is, it is hard to wirelessly charge the phone through the metal.

Magsafe can do several different things. Obviously, it can attach the phone magnetically. However, since it is a ring shape, you can still have a charging coil in the middle of the ring. Better still, the Magsafe system will align the phone and charger with a satisfying click when you put them together.

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BlackBerry Keyboard Makes This Handheld Pi Stand Out

February 25, 2025 by 2 Comments

In the decade or more since small inexpensive Linux-capable single board computers such as the Raspberry Pi came to the mainstream, many a hardware hacker has turned their attention to making a portable computer using one. With such a plethora of devices having been made one might think that the Pi handheld was a done deal, but every so often along comes a new one of such quality to re-ignite the genre. So it is with [Taylor Hay]’s BlackberryPi Handheld. As you might guess from the name, it uses a BlackBerry keyboard along with a square LCD screen to create a beautifully executed Pi handheld in an almost GameBoy-like form factor.

It starts with a beautifully designed and executed case that holds a Pi and a Pimoroni HyperPixel screen. Unexpectedly this is a full-size Pi, we think a Pi 4. The keyboard is a USB enhanced Blackberry module which also has the famous trackpad, and there’s a bezel on the front to protect the screen. The power meanwhile comes from three 18650 cells inside the back of the case, with a power bank PCB. The surprise here is how simple he’s made it by careful choice of modules, the usual rats-nest of wires is missing.

The files are available so you can make your own, and he’s actively encouraging people to remix and improve it. We like this project, a lot, and after you’ve seen the video below the break, we think you will too. Oddly, this isn’t the first time we’ve seen someone try this combination.

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PCB Dielectric Constant Measurements, Three Ways

February 25, 2025 by 2 Comments

FR4 is FR4, right? For a lot of PCB designs, the answer is yes — the particular characteristics of the substrate material don’t impact your design in any major way. But things get a little weird up in the microwave range, and having one of these easy methods to measure the dielectric properties of your PCB substrate can be pretty handy.

The RF reverse-engineering methods [Gregory F. Gusberti] are deceptively simple, even if they require some fancy test equipment. But if you’re designing circuits with features like microstrip filters where the permittivity of the substrate would matter, chances are pretty good you already have access to such gear. The first method uses a ring resonator, which is just a PCB with a circular microstrip of known circumference. Microstrip feedlines approach but don’t quite attach to the ring, leaving a tiny coupling gap. SMA connectors on the feedline connect the resonator to a microwave vector network analyzer in S21 mode. The resonant frequencies show up as peaks on the VNA, and can be used to calculate the effective permittivity of the substrate.

Method two is similar in that it measures in the frequency domain, but uses a pair of microstrip stubs of different lengths. The delta between the lengths is used to cancel out the effect of the SMA connectors, and the phase delay difference is used to calculate the effective permittivity. The last method is a time domain measurement using a single microstrip with a couple of wider areas. A fast pulse sent into this circuit will partially reflect off these impedance discontinuities; the time delay between the reflections is directly related to the propagation speed of the wave in the substrate, which allows you to calculate its effective permittivity.

One key takeaway for us is the concept of effective permittivity, which considers the whole environment of the stripline, including the air above the traces. We’d imagine that if there had been any resist or silkscreen near the traces it would change the permittivity, too, making measurements like these all the more important.

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