When Transistor Count Mattered

December 1, 2024 by Jenny List 29 Comments

Many Hackaday readers have an interest in retro technology, but we are not the only group who scour the flea markets. Alongside us are the collectors, whose interest is as much cultural as it is technological, and who seek to preserve and amass as many interesting specimens as they can. From this world comes [colectornet], with a video that crosses the bridge between our two communities, examining the so-called transistor wars of the late 1950s and through the ’60s. Just as digital camera makers would with megapixels four or five decades later, makers of transistor radios would cram as many transistors as they could into their products in a game of one-upmanship.

A simple AM transistor radio can be made with surprisingly few components, but for a circuit with a reasonable performance they suggest six transistors to be the optimal number. If we think about it we come up with five and a diode, that’s one for the self-oscillating mixer, one for IF, an audio preamplifier, and two for the audio power amplifier, but it’s possible we’re not factoring in the relatively low gain of a 1950s transistor and they’d need that extra part. In the cut-throat world of late ’50s budget consumer electronics though, any marketing ploy was worth a go. As the price of transistors tumbled but their novelty remained undimmed, manufacturers started creating radios with superfluous extra transistors, even sometimes going as far as to fit transistors which served no purpose. Our curious minds wonder if they bought super-cheap out-of-spec parts to fill those footprints.

The video charts the transistor wars in detail, showing us a feast of tiny radios, and culminating in models which claim a barely credible sixteen transistors. In a time when far more capable radios use a fraction of the board space, the video below the break makes for a fascinating watch.

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Make Your Own Point Contact Transistor

August 31, 2024 by Jenny List 22 Comments

Beyond the power variant, it sometimes seems as though we rarely encounter a discrete transistor these days, such has been the advance of integrated electronics. But they have a rich history, going back through the silicon era to germanium junction transistors, and thence to the original devices. if you’ve ever looked at the symbol for a transistor and wondered what it represents, it’s a picture of those earliest transistors, which were point contact devices. A piece of germanium as the base had two metal electrodes touching it as the emitter or collector, and as [Marcin Marciniak] shows us, you can make one yourself (Polish language, Google Translate link).

These home made transistors sacrifice a point contact diode to get the small chip of germanium, and form the other two electrodes with metal foil glued to paper. Given that germanium point contact diodes are themselves a rarity these days we’re guessing that some of you will be wincing at that. The video below is in Polish so you’ll have to enable YouTube’s translation if you’re an Anglophone — but we understand that the contact has to be made by passing a current through it, and is then secured with a drop of beeswax.

A slight surprise comes in how point contact transistors are used, unlike today’s devices their gain in common emitter mode was so poor that they took instead a common base configuration. There’s a picture of a project using three of them, a very period radio receiver with bulky transformers between all stages.

If you’re interested in more tales of home made early transistors, read our feature on Rufus Turner.

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A Simple Liquid Level Indicator With A Single IC

July 25, 2024 by Lewin Day 14 Comments

Often, the only liquid level indicator you need is your eyes, such as when looking at your cold beverage on a summer’s day. Other times, though, it’s useful to have some kind of indicator light that can tell you the same. [Hulk] shows us how to build one for a water tank using a single IC and some cheap supporting components.

If you’re unfamiliar with the ULN2003, it’s a simple Darlington transistor array with seven transistors inside. It can thus be used to switch seven LEDs without a lot of trouble. In this case, green, yellow, and red LEDs were hooked up to the outputs of the transistors in the ULN2003. Meanwhile, the base of each transistor is connected to an electrode placed at a different height in the water tank. A further positive electrode is placed in the tank connected to 12 volts. As the water raises to the height of each electrode, current flow from the base to the positive electrode switches the corresponding transistor on, and the LED in turn. Thus, you have a useful liquid level indicator with seven distinct output levels.

It’s a neat build that might prove useful if you need to check levels in a big opaque tank at a glance. Just note that it might need some maintenance over time, as the electrodes are unlikely to remain completely corrosion free if left in water. We’ve seen some other great uses of the ULN2003 before, too. Video after the break.

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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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Homebrew Computer From The Ground Up

May 26, 2024 by Bryan Cockfield 12 Comments

Building a retro computer of some sort is a rite of passage for many of us, with some building replicas or restorations of old Commodores, Ataris, and other machines from decades past. Others go even further back, to the time of the Intel 8008 or earlier, and a dedicated few will build something completely novel. This project from [3DSage] falls squarely in the latter category, with his completely DIY computer built component by component from scratch, including the machine code needed to run it.

[3DSage] starts with the backbone of every computer: the clock. He first demonstrates how a pair of NOT gates with a set of capacitors can be used as a rudimentary clock pulse, then builds a more refined version with a 555 timer and potentiometer for adjustable rates. Then, it’s on to creating a binary counter, which is a fundamental part of the memory system for this small computer, and finally, allows this circuitry to behave like a normal computer. Using a set of switches to store values in memory and stepping through them with the clock, the computer can be programmed to do plenty of tasks just like a modern microcontroller.

[3DSage] built this project a few years ago and has used it for real-world applications such as controlling servos, LED arrays, playing music, and other tasks. Although he has to program it using his own machine code by hand, it’s a usable computer in many ways. If you want to eschew modernity and build a retro computer in the style of the 1960s, though, this piece goes through what it would have been like to build a similar system in the era when these computers were more common. If you have a switch fetish, you might like to see how real computers worked back then, too.

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Reprogrammable Transistors

March 26, 2024 by Bryan Cockfield 21 Comments

Not every computer can make use of a disk drive when it needs to store persistent data. Embedded systems especially have pushed the development of a series of erasable programmable read-only memories (EPROMs) because of their need for speed and reliability. But erasing memory and writing it over again, whether it’s an EPROM, an EEPROM, an FPGA, or some other type of configurable solid-state memory is just scratching the surface of what it might be possible to get integrated circuits and their transistors to do. This team has created a transistor that itself is programmable.

Rather than doping the semiconductor material with impurities to create the electrical characteristics needed for the transistor, the team from TU Wien in Vienna has developed a way to “electrostatically dope” the semiconductor, using electric fields instead of physical impurities to achieve the performance needed in the material. A second gate, called the program gate, can be used to reconfigure the electric fields within the transistor, changing its properties on the fly. This still requires some electrical control, though, so the team doesn’t expect their new invention to outright replace all transistors in the future, and they also note that it’s unlikely that these could be made as small as existing transistors due to the extra complexity.

While the article from IEEE lists some potential applications for this technology in the broad sense, we’d like to see what these transistors are actually capable of doing on a more specific level. It seems like these types of circuits could improve efficiency, as fewer transistors might be needed for a wider variety of tasks, and that there are certainly some enhanced security features these could provide as well. For a refresher on the operation of an everyday transistor, though, take a look at this guide to the field-effect transistor.

A Transistor, But For Heat Instead Of Electrons

December 20, 2023 by Donald Papp 31 Comments

Researchers at UCLA recently developed what they are calling a thermal transistor: a solid-state device able to control the flow of heat with an electric field. This opens the door to controlling the transfer of heat in some of the same ways we are used to controlling electronics.

Heat management can be a crucial task, especially where electronics are involved. The usual way to manage heat is to draw it out with things like heat sinks. If heat isn’t radiating away fast enough, a fan can be turned on (or sped up) to meet targets. Compared to the precision and control with which modern semiconductors shuttle electrons about, the ability to actively manage heat seems lacking.

This new device can rapidly adjust thermal conductivity of a channel based on an electrical field input, which is very similar to what a transistor does for electrical conductivity. Applying an electrical field modifies the strength of molecular bonds in a cage-like array of molecules, which in turn adjusts their thermal conductivity.

It’s still early, but this research may open the door to better control of heat within semiconductor systems. This is especially interesting considering that 3D chips have been picking up speed for years (stacking components is already a thing, it’s called Package-on-Package assembly) and the denser and deeper semiconductors get, the harder it is to passively pull heat out.

Thanks to [Jacob] for the tip!