Making A Solid State 6AK8 Tube

July 22, 2024 by Al Williams 13 Comments

[M Caldeira] had a project in mind: replacing a common vacuum tube with a solid-state equivalent. The tube in question was an EABC80 or 6AK8 triple diode triode. The key was identifying a high-voltage FET and building it, along with some other components, into a tube base to make a plug-in replacement for the tube. You can see a video about the project below.

These tubes are often used as a detector and preamplifier. Removing the detector tube from a working radio, of course, kills the audio. Replacing the tube with a single diode restores the operation of the radio, although at a disadvantage.

From there, he adds more diodes directly into the socket. Of course, diodes don’t amplify, so he had to break out a LND150 MOSFET with a limit of 500 volts across the device. It takes some additional components, and the whole thing fits in a tube base ready for the socket.

Usually, we see people go the other way using tubes instead of transistors in, say, a computer. If you want real hacking, why not make your own tubes?

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All About PNP Transistors

July 21, 2024 by Al Williams 21 Comments

In the early days, PNP bipolar transistors were common, but the bulk of circuits you see today use NPN transistors. As [Aaron Danner] points out, many people think PNP transistors are “backward” but they have an important role to play in many circuits. He explains it all in a recent video you can see below.

He does explain why PNP transistors don’t perform as well as corresponding NPN transistors, but they are still necessary sometimes. Once you get used to it, they are no problem to handle at all. Common cases where you want a PNP are, for example, when you want to switch a voltage instead of a ground. There are also certain amplifier configurations that need PNP units.

Like an NPN transistor, a PNP can operate in saturation, linear operation, reverse active, or it can be cut off. [Aaron] shows you how to bias a transistor and you’ll see it isn’t much different from an NPN except the base-emitter diode junction is reversed.

As you might expect, current has to flow through that diode junction to turn the transistor on. The arrow points in the direction of the diode junction. If you want a refresher on transistor biasing, we got you. Sure, you don’t need to do it every day now, but it still is a useful skill to have.

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Working Through The Art Of Electronics Exercises

July 20, 2024 by Al Williams 10 Comments

[The Engineering Experience] has an ambitious series of videos. He’s working through circuit examples from the awesome book “The Art of Electronics.” In the latest installment, he’s looking at a pulse generator that uses bipolar transistors. So far, there are 43 videos covering different exercises.

If you’ve read the book — and you should — you know the examples and exercises sometimes have little explanation. Honestly, that’s good. You should try to work through them yourself first. But once you have an idea of how it works, hearing someone give their take on it may help you out. In fact, even if you don’t have the book, we’d suggest pausing the video and looking at the circuit to see what you can figure out before playing the explanation. You’ll learn more that way.

Admittedly, some of the early videos will be cakewalks for Hackaday readers. The first few, for example, walk through parallel and series resistors. However, if you are starting out or just want a refresher, you can probably enjoy all of them. The later ones get a bit more challenging.

If you want to double-check your work, you can simulate the circuit, too. Our simulation got 4.79 V and he computed 4.8, which is certainly close enough.

We do love “The Art of Electronics.” The book’s author also enjoys listening for aliens.

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How Ten Turn Pots Are Made

July 19, 2024 by Al Williams 5 Comments

It is easy to think of a potentiometer as a simple device, but there are many nuances. For example, some pots are linear — a change of a few degrees at the low end will change the resistance the same amount as the same few degrees at the high end. Others are logarithmic. Changes at one end of the scale are more dramatic than at the other end of the scale. But for very precise use, you often turn to the infamous ten-turn pot. Here, one rotation of the knob is only a tenth of the entire range. [Thomas] shows us what’s inside a typical one in the video below.

When you need a precise measurement, such as in a bridge instrument, these pots are indispensable. [Thomas] had a broken one and took that opportunity to peer inside. The resistor part is a coil of wire wound around the inside of the round body. Unsurprisingly, there are ten turns of wire that make up the coil.

The business end, of course, is in the rotating part attached to the knob. A small shuttle moves up and down the shaft, making contact with the resistance wire and a contact for the wiper. The solution is completely mechanical and dead simple.

As [Thomas] notes, these are usually expensive, but you can — of course — build your own. These are nice for doing fine adjustments with precision power supplies, too.

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Playing Rock, Paper Scissors With A Time Of Flight Sensor

July 16, 2024 by Lewin Day 3 Comments

You can do all kinds of wonderful things with cameras and image recognition. However, sometimes spatial data is useful, too. As [madmcu] demonstrates, you can use depth data from a time-of-flight sensor for gesture recognition, as seen in this rock-paper-scissors demo.

If you’re unfamiliar with time-of-flight sensors, they’re easy enough to understand. They measure distance by determining the time it takes photons to travel from one place to another. For example, by shooting out light from the sensor and measuring how long it takes to bounce back, the sensor can determine how far away an object is. Take an array of time-of-flight measurements, and you can get simple spatial data for further analysis.

The build uses an Arduino Uno R4 Minima, paired with a demo board for the VL53L5CX time-of-flight sensor. The software is developed using NanoEdge AI Studio. In a basic sense, the system uses a machine learning model to classify data captured by the time-of-flight sensor into gestures matching rock, paper, or scissors—or nothing, if no hand is present. If you don’t find [madmcu]’s tutorial enough, you can take a look at the original version from STMicroelectronics, too.

It takes some training, and it only works in the right lighting conditions, but this is a functional system that can determine real hand sign and play the game. We’ve seen similar techniques help more advanced robots cheat at this game before, too! What a time to be alive.

You Can Use A CRT As An Audio Amplifier Tube

July 11, 2024 by Lewin Day 36 Comments

When we talk about audio amplifier tubes, we’re normally talking about the glass little blobby things you might find in a guitar amplifier. We’re not normally talking about big ol’ color CRTs, but apparently they can do the job too. That’s what [Termadnator] is here to show us.

The CRT in question is a 14″ unit from a common garden variety Philips color TV. [Termadnator] pulled out the TV’s original circuitry, and replaced much of it with his own. He had to whip up a high-voltage power supply with a 555 and a laptop power supply, along with a bunch of fake MOSFETs pressed into service. He also had to build his own Leyden jar capacitor, too. The specifics of converting it to audio operation get a bit messy, but fear not—[Termadnator] explains the idea well, and also supplies a schematic. Perhaps the coolest thing, though, is the crazy color pattern that appears on the display when it’s working as an amp.

Sound output isn’t exactly loud, and it’s a little distorted, too. Still, it’s amusing to see an entire TV instead doing the job of a single amplifier tube. Video after the break.

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A New Raspberry 5 DSI Cable Makes Using Screens Easier

July 10, 2024 by Lewin Day 8 Comments

Arguably the greatest strength of the Raspberry Pi is the ecosystem — it’s well-supported by its creators and the aftermarket. At the same time, the proliferation of different boards has made things more complicated over the years. Thankfully, though, the community is always standing by to help fix any problems. [Rastersoft] has stepped up in this regard, solving an issue with the Raspberry Pi 5 and DSI screen cables.

The root cause is that the DSI cable used on the Raspberry Pi 5 has changed relative to earlier boards. This means that if you use the Pi 5 with many existing screens and DSI cables, you’ll find your flat ribbon cable gets an ugly twist in it. This can be particularly problematic when using the cables in tight cases, where they may end up folded, crushed, or damaged.

[Rastersoft] got around this by designing a new cable that avoided the problem. It not only solves the twist issue, but frees up space around the CPU if you wish to use a cooler. Thanks to modern PCB houses embracing flexible boards, it’s easy to get it produced, too.

This is a great example of the democratization of PCB and electronics production in general. 20 years ago, you wouldn’t be able to make a flex cable like this without ordering 10,000 of them. Today, you can order a handful for your own personal use, and share the design with strangers on a whim. Easy, huh? It’s a beautiful world we live in.