Over The Counter Glucose Monitor Dissected

February 23, 2025 by Al Williams 33 Comments

If you deal with diabetes, you probably know how to prick your finger and use a little meter to read your glucose levels. The meters get better and better which mostly means they take less blood, so you don’t have to lacerate your finger so severely. Even so, taking your blood several times a day is hard on your fingertips. Continuous monitoring is available, but — until recently — required a prescription and was fairly expensive. [Andy] noticed the recent introduction of a relatively inexpensive over-the-counter sensor, the Stelo CGM. Of course, he had to find out what was inside, and thanks to him, you can see it, too.

If you haven’t used a continuous glucose monitor (CGM), there is still a prick involved, but it is once every two weeks or so and occurs in the back of your arm. A spring drives a needle into your flesh and retracts. However, it leaves behind a little catheter. The other end of the catheter is in an adhesive-backed module that stays put. It sounds a little uncomfortable, but normally, it is hardly noticeable, and even if it is, it is much better than sticking your finger repeatedly to draw out a bunch of blood.

Continue reading “Over The Counter Glucose Monitor Dissected” →

Behind The Lens: Tearing Down A Rare Soviet Zenit 19

February 23, 2025 by Heidi Ulrich 3 Comments

If you’re into Soviet-era gear with a techy twist, you’ll love this teardown of a rare Zenit 19 camera courtesy of [msylvain59]. Found broken on eBay (for a steal!), this 1982 made-in-USSR single-lens reflex camera isn’t the average Zenit. It features, for example, electronically controlled shutter timing – quite the upgrade from its manual siblings.

The not-so-minor issue that made this Zenit 19 come for cheap was a missing shutter blade. You’d say – one blade gone rogue! Is it lost in the camera’s guts, or snapped clean off? Add to that some oxidized battery contacts and a cracked viewfinder, and you’ve got proper fixer-upper material. But that’s where it gets intriguing: the camera houses a rare hybrid electronic module (PAPO 074), complete with epoxy-covered resistors. The shutter speed dial directly adjusts a set of resistors, sending precise signals to the shutter assembly: a neat blend of old-school mechanics and early electronics.

Now will it shutter, or stutter? With its vertical metal shutter – uncommon in Zenits – and separate light metering circuitry, this teardown offers a rare glimpse into Soviet engineering flair. Hungry for more? We’ve covered a Soviet-era computer and a radio in the past. If you’re more into analog camera teardowns, you might like this analog Pi upgrade attempt, or this bare minimum analog camera project.

Continue reading “Behind The Lens: Tearing Down A Rare Soviet Zenit 19” →

Reviewing A Very Dodgy BSK-602 Adjustable Power Supply

February 21, 2025 by Maya Posch 16 Comments

There’s no shortage of cheap & cheerful power supplies which you can obtain from a range of online retailers, but with no listed certification worth anything on them calling them ‘dodgy’ is more of a compliment. On the [DiodeGoneWild] YouTube channel an adjustable power supply by the model name BSK-602 is tested and torn down to see exactly what less than $5 off sites like Alibaba will get you.

Perhaps unsurprisingly, voltage regulation is very unstable with massive drifting when left to heat up for a few hours, even though it does hit the 3 V to 24 V DC and 3 A output that it’s optimistically rated for. After popping open the adapter, a very basic switching mode power supply is revealed with an abysmal component selection and zero regard for safety or primary and secondary side isolation. With the case open, the thermal camera reveals that the secondary side heats up to well over 150 °C, explaining why the case was deforming and the sticker peeling off after a few hours of testing.

The circuit itself is based around a (possibly legit) UC3843RN 500 kHz current mode PWM controller, with the full schematic explained in the video. Highlights include the lack of inrush protection, no EMI filtering, a terrible & temperature-dependent voltage reference, not to mention poor component selection and implementation. Basically it’s an excellent SMPS if you want to blast EMI, fry connected electronics and conceivably burn down your home.

Continue reading “Reviewing A Very Dodgy BSK-602 Adjustable Power Supply” →

Repairing An Old Heathkit ‘Scope

February 8, 2025 by Al Williams 8 Comments

With so many cheap oscilloscopes out there, the market for old units isn’t what it used to be. But if you have a really old scope, like the Heathkit O-10 that [Ken] found in his basement, there is vintage cred to having one. [Ken’s] didn’t work, so a repair session ensued. You can see the results in the video below.

You can tell this is in an old scope — probably from the mid 1950s — because of its round tube with no graticle. Like many period scopes, the test probe input was just 5-way binding posts. The O-10 was the first Heathkit “O-series” scope that used printed circuit boards.

The device looked pretty good inside, except for a few dents. Of course, the box has tubes in it, so every power up test involves waiting for the tubes to warm up. [Ken] was very excited when he finally got a single green dot on the screen. That did, however, require a new CRT.

It wasn’t long after that he was able to put a waveform in and the scope did a good job of reproducing it. The unit would look good in an old movie, but might not be the most practical bench instrument these days.

These Heathkit scopes and their cousins were very popular in their day. The $70 price tag sounds cheap, but in the mid-1950s, that was about a month’s rent in a four-room house. While primitive by today’s standards, scopes had come a long way in 9 or 10 years.

Continue reading “Repairing An Old Heathkit ‘Scope” →

Understanding The T12 Style Soldering Iron Tip

February 4, 2025 by Maya Posch 16 Comments

Soldering irons and their tips come in a wide range of formats and styles, with the (originally Hakko) T12 being one of the more interesting offerings. This is because of how it integrates not only the tip and heating element, but also a thermocouple and everything else in a self-contained package. In a recent video [Big Clive] decided to not only poke at one of these T12 tips, but also do a teardown.

These elements have three bands, corresponding to the power supply along with a contact for the built-in thermocouple. After a quick trip to the Vise of Knowledge, [Clive] allows us a glimpse at the mangled remnants of a T12, which provides a pretty good overview of how these tips are put together.

Perhaps unsurprisingly, most of the length is a hollow tube through which the wires from the three contacts run. These power the ceramic heating element, as well as provide the soldering iron handle access to the thermocouple that’s placed near the actual tip.

With a simple diagram [Clive] explains how these T12 elements are then used to regulate the temperature, which isn’t too distinct from the average soldering iron with ceramic heating element, but it’s still nice to have it all integrated rather than having to try to carefully not damage the ceramic heater while swapping tips with the average soldering iron.

Continue reading “Understanding The T12 Style Soldering Iron Tip” →

Stepper Motor Operating Principle And Microstepping Explained

February 3, 2025 by Maya Posch 14 Comments

The [Denki Otaku] YouTube channel took a look recently at some stepper motors, or ‘stepping motors’ as they’re called in Japanese. Using a 2-phase stepper motor as an example, the stepper motor is taken apart and its components explained. Next a primer on the types and the ways of driving stepper motors is given, providing a decent overview of the basics at the hand of practical examples.

As great as theoretical explanations are, there’s a lot of value in watching the internals of a stepper motor move when its coils are activated in order. Also demonstrated are PWM-controlled stepper motor drivers before diving into the peculiarities of microstepping, whereby the driving of the coils is done such that the stator moves in the smallest possible increments, often through flux levels in these coils. This allows for significantly finer positioning of the output shaft than with wave stepping and similar methods that are highly dependent on the number of phases and coils.

As demonstrated in the video, another major benefit of microstepping is that it creates much smoother movement while moving, but also noted is that servo motors are often what you want instead. This is a topic which we addressed in our recent article on the workings of stepper motors, with particular focus on the 4-phase 28BYJ-48 stepper motor and the disadvantages of steppers versus servos.

Continue reading “Stepper Motor Operating Principle And Microstepping Explained” →

Inside A Vintage Oven Controlled Crystal Oscillator

February 1, 2025 by Maya Posch 8 Comments

Crystal oscillators are incredibly useful components, but they come with one little snag: their oscillation is temperature-dependent. For many applications the relatively small deviation is not a problem, but especially for precision instruments this is a deal breaker. Enter the oven controlled crystal oscillator, or OCXO. These do basically what it says on the tin, but what’s inside them? [Kerry Wong] took apart a vintage Toyocom TCO-627VC 10 MHz OCXO, revealing a lot more complexity than one might assume.

Inside the insulated enclosure there is of course the crystal oscillator itself, which has a heating coil wrapped around it. Of note is that other OCXOs that [Kerry] took apart had more insulation, as well as other ways of providing the thermal energy. In this particular unit a thermistor is attached to the crystal’s metal case to measure its temperature and provide feedback to the heating circuit. The ICs on the PCB are hard to identify due to the conformal coating, but at least one appears to be a 74LS00, alongside a 78L05 voltage regulator which reduces the 12V input voltage.

As an older OCXO it probably is a lot chunkier than newer units, but the basic principle remains the same, with a heating loop that ensures that the crystal inside the unit remains at the same temperature.

Continue reading “Inside A Vintage Oven Controlled Crystal Oscillator” →