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.

Continue reading “Make Your Own Point Contact Transistor” →

A Non-Musical Use Case For 8-Track

August 28, 2024 by Bryan Cockfield 23 Comments

There was a time in the not-too-distant past when magnetic tape was the primary way of listening to and recording audio. Most of us are familiar with the cassette tape, a four-track system that plays first one side of the tape, then the other. There was the eight-track tape as well which did not have quite as much popularity or longevity but did have a few interesting features that [Serial Hobbyism] took advantage of to make an interactive game.

The defining feature of the eight-track system, beyond the obvious eight tracks on the tape, is that the tape runs in a continuous loop, never needing to be stopped or flipped over. Instead, four buttons select pairs of the eight tracks, moving a head immediately to make the switch on-the-fly. [Serial Hobbyism]’s game plays a trivia-style audio recording and asks the player to answer questions by pushing one of the four “program” buttons to switch tracks. If the correct track is selected, the recorded audio congratulates the player and then continues on with the game. Likewise, if an incorrect track is selected, the recording notes that and the game continues.

Another interesting feature of this game is that it can be played without modifying an eight-track player, as the selectable tracks are a core function of this technology. They can be used in a similar way as cassette tapes to store computer data and a data recorder similar to the eight-track system was used on the Voyager space probes, although these only bear a passing resemblance.

Continue reading “A Non-Musical Use Case For 8-Track” →

A Journey Into Unexpected Serial Ports

August 24, 2024 by Jenny List 17 Comments

Through all the generations of computing devices from the era of the teleprinter to the present day, there’s one interface that’s remained universal. Even though its usefulness as an everyday port has decreased in the face of much faster competition, it’s fair to say that everything has a serial port on board somewhere. Even with that ubiquity though, there’s still some scope for variation.

Older ports and those that are still exposed via a D socket are in most case the so-called RS-232, a higher voltage port, while your microcontroller debug port will be so-called TTL (transistor-transistor logic), operating at logic level. That’s not quite always the case though, as [Terin Stock] found out with an older Garmin GPS unit.

Pleasingly for a three decade old device, given a fresh set of batteries it worked. The time was wrong, but after some fiddling and a Windows 98 machine spun up it applied a Garmin update from 1999 that fixed it. When hooked up to a Flipper Zero though, and after a mild panic about voltage levels, the serial port appeared to deliver garbage. There followed some investigation, with an interesting conclusion that TTL serial is usually the inverse of RS-232 serial, The Garmin had the RS-232 polarity with TTL levels, allowing it to work with many PC serial ports. A quick application of an inverter fixed the problem, and now Garmin and Flipper talk happily.

Simple 3D-Printed Table Loom For Complex Weavings

August 17, 2024 by Heidi Ulrich 17 Comments

The loom has been a transformative invention throughout history, shaping the textile industry from simple hand looms to complex, fully automated machines. Now, thanks to advancements in 3D printing, this age-old craft is being revitalized by modern makers. One such creator, [Fraens], has recently designed a unique 3D-printed table loom with eight shafts, offering a simpler yet innovative approach to weaving. This project is a fresh take on traditional looms, blending centuries of design knowledge with contemporary technology.

[Fraens], a longtime enthusiast of looms, has spent considerable time studying the countless designs that have evolved over more than 200 years. Drawing inspiration from these, he has crafted a more accessible version—a table loom that can be operated using levers to control the warp threads. Unlike larger, more complex looms, this 3D-printed model allows users to experiment with various weaving patterns easily, using different colors and sequences to create beautiful, intricate designs. [Fraens] provides guidance on how to adapt patterns meant for larger looms to this compact, lever-operated version on his website and in a detailed video tutorial.

This project is perfect for anyone interested in weaving or DIY technology. [Fraens]’ 3D-printed loom offers a new way to explore textile creation, making it both approachable and rewarding. To see this innovative loom in action and learn how to build your own, check out the video below.

Continue reading “Simple 3D-Printed Table Loom For Complex Weavings” →

Homebrew Relay Computer Features Motorized Clock

August 3, 2024 by Tom Nardi 6 Comments

Before today, we probably would have said that scratch-built relay computers were the sole domain of only the most wizardly of graybeards. But this impressive build sent in by [Will Dana] shows that not only are there young hardware hackers out there that are still bold enough to leave the transistor behind, but that they can help communicate how core computing concepts can be implemented with a bundle of wires and switches.

Created for his YouTube channel WillsBuilds, every component of this computer was built by [Will] himself. Each of the nine relay-packed protoboards inside the machine took hours to solder, and when that was done, he went out to the garage to start cutting the wood that would become the cabinet they all get mounted in.

Continue reading “Homebrew Relay Computer Features Motorized Clock” →

A Simple Liquid Level Indicator With A Single IC

July 25, 2024 by Lewin Day 15 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.

Continue reading “A Simple Liquid Level Indicator With A Single IC” →

Need A Tube? Reach For Plywood!

July 23, 2024 by Al Williams 14 Comments

To be clear, when we are talking about tubes, we mean ordinary cylinders, not vacuum-amplifying elements. With that out of the way, when we need a tube like that, we usually think of PVC or some other kind of pipe product. Or maybe we’ll 3D print what we need. But not [GregO29]. He made his tubes from plywood.

You can make tubes as small as 12 inches in diameter, and [GregO29] made some that were 16 inches. The first step was to make a mold or form. In this case, he elected to make a form that the tube-to-be wraps around. The plywood is thin 2-ply white birch. This makes it easy to shape.

The basic idea is to wrap the wood around the form and glue it. You hold it together with a strap until it dries. Then, you can add more layers until it is the thickness you need.

The real problem turned out to be removing the form once it was done. Why make a tube like this? In [Greg]’s case, he’s building a telescope, which is as good a reason as any to have a tube, we suppose.

We build a lot of things, but we always forget about plywood. It even mixes well with electricity.