pots

22 Articles

Old Czech Telephone Teardown Is Beautiful Purposeful Art

April 18, 2023 by 16 Comments

The 20th century saw everything from telephones to computers become mainstream. Many of these devices were beautifully designed in the mid-century period, something that’s hard to say about a lot of today’s cheaper technology. [John Graham-Cumming] has shown us one exquisite example, with his teardown of a simple Czech telephone.

The model in question is a DS3600 telephone built by Tesla Stropkov in the early 1980s. Despite this, it’s a design that looks like it hails more from the 1960s based on its smooth curves and rounded features. It’s a rotary dial phone, though a push-button version was also produced.

Inside the phone is a simple single-sided PCB clearly marked out with a tidy silkscreen. The ringer and a few capacitors make up the bulk of the circuitry inside the base, along with the rotary dial. The handset itself plays host to most of the other componentry, including the mystery “WNB 068 hybrid circuit” which [John] couldn’t positively identify.

It’s great to get a look inside vintage hardware and see how things were done in yesteryear. It’s particularly funny to think about how simple telephones used to be in contrast to today.

[Thanks to Saint Aardvark for the tip!]

Homebrew Telephone Exchange Keeps The Family In Touch, In The House And Beyond

January 14, 2023 by 4 Comments

It doesn’t happen often, but every once in a while we stumble upon someone who has taken obsolete but really cool phone-switching equipment and built a private switched telephone in their garage or basement using it. This private analog phone exchange is not one of those, but it’s still a super cool build that’s probably about as ambitious as getting an old step-by-step or crossbar switch running.

Right up front, we’ll stipulate that there’s absolutely no practical reason to do something like this. And hacker [Jon Petter Skagmo] admits that this is very much a “because I can” project. The idea is to support a bunch of old landline phones distributed around the house, and beyond, in a sort of glorified intercom system. The private exchange is entirely scratch-built, with a PIC32 acting as the heart of the system, performing such tasks as DTMF decoding, generating ring voltage, and even providing a CAN bus interface to his home automation system.

The main board supports five line interface daughterboards, which connect each phone to the switch via an RJ11 jack. The interface does the work of detecting when a phone goes off-hook, and does the actual connection between any two phones. A separate, special interface card provides an auto-patch capability using an RDA1846S RF transceiver module; with it, [Jon Petter] can connect to any phone in the system from a UHF handy-talkie. Check out the video below for more on that — it’s pretty neat!

We just love everything about this overengineered project — it’s clearly a labor of love, and the fit and finish really reflect that. And even though it’s not strictly old school, POTS projects like this always put us in the mood to watch the “Speedy Cutover” video one more time.

Continue reading “Homebrew Telephone Exchange Keeps The Family In Touch, In The House And Beyond” →

Several relays and switches mounted on a metal frame

The Simplest Electro-Mechanical Telephone Exchange That Actually Works

April 14, 2022 by 34 Comments

While rarely seen by users, the technology behind telephone exchanges is actually quite interesting. In the first hundred or so years of their existence they evolved from manually-operated switchboards to computer-controlled systems, but in between those two stages was a time when dialling and switching was performed electromechanically. This was made possible by the invention of the stepping switch, a type of pulse-operated relay that can connect a single incoming wire to one of many outgoing wires.

Public telephone exchanges contained hundreds of these switches, but as [dearuserhron] shows, it’s possible to make a smaller system with way fewer components: the Cadr-o-station is built around one single stepper switch. Although it looks rather complicated, the only other components are a bunch of ordinary 24 V relays and a few power supplies. Together they make up a minimal telephone exchange that connects up to ten handsets.

It doesn’t have all the functionality of a larger system however, as only a single voice circuit is made to which all phones are automatically connected. Still, it does allow users to dial a number and let the other phone ring, which might be good enough for a home or indeed the hackerspace where it’s currently sitting. It’s also a fine demonstration of how relatively simple technology can be applied to make a surprisingly complex system.

[dearuserhron] wrote an in-depth article on the workings of electromechanical telephone exchanges, which might come in helpful to anyone who’d like to design such a system for their own home. For a more general introduction into analog phone technology, check out our analysis of a 1970s rotary telephone.

Continue reading “The Simplest Electro-Mechanical Telephone Exchange That Actually Works” →

Hackaday Links Column Banner

Hackaday Links: September 5, 2021

September 5, 2021 by 7 Comments

Good news from Jezero crater as the Mars rover Perseverance manages to accomplish for the first time what it was sent to do: collect and cache core samples from rocks. Space buffs will no doubt recall that Perseverance’s first attempt at core sampling didn’t go as planned — the rock that planetary scientists selected ended up being too soft, and the percussive coring bit just turned the core sample into powder. The latest attempt went exactly as planned: the cylindrical coring bit made a perfect cut, the core slipped into the sample tube nested inside the coring bit, and the core broke off cleanly inside the sample tube when it was cammed off-axis. Operators were able to provide visible proof that the core sample was retained this time using the Mastcam-Z instrument, which clearly shows the core in the sample tube. What’s neat is that they then performed a “percuss to ingest” maneuver, where the coring bit and sample tube are vibrated briefly, so that the core sample and any dust grains left around the sealing rim slide down into the sample tube. The next step is to transfer the sample tube to the belly of the rover where it’ll be hermetically sealed after some basic analysis.

Did any Android users perhaps oversleep this week? If you did, you’re not alone — lots of users of the Google Clock app reported that their preset alarms didn’t go off. Whether it was an actual issue caused by an update or some kind of glitch is unclear, but it clearly didn’t affect everyone; my phone mercilessly reminded me when 6:00 AM came around every day last week. But it apparently tripped up some users, to the point where one reported losing his job because of being late for work. Not to be judgmental, but it seems to me that if your job is so sensitive to you being late, it might make sense to have a backup alarm clock of some sort. We all seem to be a little too trusting that our phones are going to “just work,” and when they don’t, we’re surprised and appalled.

There seem to be two kinds of people in the world — those who hate roller coasters, and those who love them. I’m firmly in the latter camp, and will gladly give any coaster, no matter how extreme, a try. There have been a few that I later regretted, of course, but by and large, the feeling of being right on the edge of bodily harm is pretty cool. Crossing over the edge, though, is far less enjoyable, as the owners of an extreme coaster in Japan are learning. The Dodon-pa coaster at the Fuji-Q Highland amusement park is capable of hitting 112 miles (180 km) per hour and has racked up a sizable collection of injuries over the last ten months, including cervical and thoracic spine fractures. The ride is currently closed for a safety overhaul; one has to wonder what they’re doing to assess what the problem areas of the ride are. Perhaps they’re sending crash test dummies on endless rides to gather data, a sight we’d like to see.

And finally, you may have thought that phone phreaking was a thing of the past; in a lot of ways, you’d be right. But there’s still a lot to be learned about how POTS networks were put together, and this phone switch identification guide should be a big help to any phone geeks out there. Be ready to roll old school here — nothing but a plain text file that describes how to probe the switch that a phone is connected just by listening to things like dial tones and ring sounds. What’s nice is that it describes why the switches sound the way they do, so you get a lot of juicy technical insights into how switches work.

Teardown: Tap Trapper

January 14, 2021 by 46 Comments

The modern consumer is not overly concerned with their phone conversations being monitored. For one thing, Google and Amazon have done a tremendous job of conditioning them to believe that electronic gadgets listening to their every word isn’t just acceptable, but a near necessity in the 21st century. After all, if there was a better way to turn on the kitchen light than having a recording of your voice uploaded to Amazon so they can run it through their speech analysis software, somebody would have surely thought of it by now.

But perhaps more importantly, there’s a general understanding that the nature of telephony has changed to the point that few outside of three letter agencies can realistically intercept a phone call. Sure we’ve seen the occasional spoofed GSM network pop up at hacker cons, and there’s a troubling number of StingRays floating around out there, but it’s still a far cry from how things were back when folks still used phones that plugged into the wall. In those days, the neighborhood creep needed little more than a pair of wire strippers to listen in on your every word.

Which is precisely why products like the TA-1356 Tap Trapper were made. It was advertised as being able to scan your home’s phone line to alert you when somebody else might be listening in, whether it was a tape recorder spliced in on the pole or somebody in another room lifting the handset. You just had to clip it onto the phone distribution panel and feed it a fresh battery once and awhile.

If the red light came on, you’d know something had changed since the Tap Trapper was installed and calibrated. But how did this futuristic defender of communications privacy work? Let’s open it up and take a look.

Continue reading “Teardown: Tap Trapper” →

Ask Hackaday: With Landline Use In Decline, What’s To Be Done With The Local Loop?

October 12, 2020 by 100 Comments

Walking is great exercise, but it’s good for the mind too: it gives one time to observe and to think. At least that’s what I do on my daily walks, and being me, what I usually observe and think about is the local infrastructure along my route. Recently, I was surprised to see a number of telephone company cabinets lying open next to the sidewalk. Usually when you see an open box, there’s a telephone tech right there, working on the system. But these were wide open and unattended, which I thought was unusual.

I, of course, took the opportunity to check out the contents of these pedestals in detail. Looking at the hundreds of pairs of brightly colored wire all neatly terminated and obviously installed and maintained at great expense, I was left wondering why someone would leave such a valuable asset exposed to the elements. With traditional POTS, or plain old telephone service, on the decline, the world may no longer have much use for the millions of miles of copper cable feeding back to telco central offices (COs) anymore. But there’s got to be something this once-vital infrastructure is still good for, leading me to ask: what’s to be done with the local loop?

Continue reading “Ask Hackaday: With Landline Use In Decline, What’s To Be Done With The Local Loop?” →

Wood And Carbon Rods Used For This Handsome And Effective Microphone

April 18, 2020 by 20 Comments

Anyone who was active in the phreaking scene or was even the least bit curious about the phone system back in the Ma Bell days no doubt remembers the carbon capsule microphone in the mouthpiece of many telephone handsets. With carbon granules sandwiched between a diaphragm and a metal plate, they were essentially sound-driven variable resistors, and they worked well enough to be the standard microphone for telephony for decades.

In an attempt to reduce complicated practices to their fundamentals, [Simplifier] has undertaken this surprisingly high-fidelity carbon microphone build that hearkens back to the early days of the telephone. It builds on previous work that was more proof of concept but still impressive. In both builds, the diaphragm of the microphone is a thin piece of wood, at first carved from a single block of softwood, then later improved by attaching a thin piece of pine to a red oak frame. The electrical side of the mic has four carbon rods running from the frame to the center of the diaphragm, where they articulate in a carbon block with small divots dug into it. As the diaphragm vibrates, the block exerts more or less pressure on the rods, varying the current across the mic and reproducing the sound. It works quite well, judging by the video after the break.

Congratulations to [Simplifier] for another great build and top-notch craftsmanship. We’ve seen homebrew vacuum tubes, conductive glass, and solar cells from him before, which sort of makes him the high-tech version of Primitive Technology. We’re looking forward to whatever comes next. Continue reading “Wood And Carbon Rods Used For This Handsome And Effective Microphone” →