telephone

56 Articles

A homebrew telephone connects home and workshop.

The Calls Are Coming From Inside The House (or Workshop)

October 19, 2021 by 16 Comments

Hot on the heels of their carbon microphone build a few years ago, [Simplifier] strung up a two-phone network between the house and the workshop. Both telephones are completely DIY except for the pair of switches on the front. Each side has a bell, a microphone, and an audio transformer. Listening is done through a pair of headphones, and both users speak through a homebrew carbon microphone.

We particularly love the bell, which is made from fence post caps. Sitting between the bells and ready to strike is a ball bearing mounted on a really thick piece of wire that’s driven by an electromagnet. To make a call, you use both switches — the one on the left pulls either the bell or the microphone to ground, while the switch on the left right is used momentarily to send 6 V from the lantern battery down the 50 ft. line to the other phone to ring it. You’ll see what we mean in the demo video after the break. Check out the sound of those fence post caps!

[Simplifier] wound an audio transformer that provides the necessary impedance matching to use regular headphones as receivers. Since the homebrew microphones only need 1.5 V, [Simplifier] split the voltage across two carbon contacts placed in series. That’s still more than necessary, but [Simplifier] was able to make it work.

More recently, [Simplifier] has built a beautiful and even better carbon microphone and even hosted a back-to-basics Hack Chat.

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Retrotechtacular: Wire Splicing The Army Way

June 11, 2020 by 31 Comments

For those of us who started experimenting with electricity when we were very young, one of the essential first skills was learning how to twist wires together. It seems like there’s not much to learn, but after a few failed attempts with nothing but your fingers, you learned a few tricks that are probably still with you to this day. It’s not surprising, then, that there’s an official US Army way to twist wires together, as this Signal Corps training film from 1941 shows.

Considering that the Signal Corps had nearly 80 years of experience with wiring battlefield communications at the outbreak of World War II, their methods were pretty solid, as were their materials. The film mainly concerns the splicing together of rolls of type W110-B field wire, used by the Signal Corps to connect command posts to forward positions, observation posts, and the rear echelons. More often than not laid directly upon the ground, the wire had to be tough, waterproof, and conductive enough that field telephone gear would still work over long loop lengths. As such, the steel-reinforced, rubber-and-fabric clad cable was not the easiest stuff to splice. Where we might cringe at the stresses introduced by literally tying a conductor in knots, it was all part of the job for the wire-laying teams that did the job as quickly as possible, often while taking enemy fire.

The film also has a section on splicing a new line into an existing, in-service circuit, using a T-splice and paying careful attention to the topology of the knots used, lest they come undone under stress. It’s fascinating how much thought was put into something as mundane as twisting wires, but given the stakes, we can appreciate the attention to detail.

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Retrotechtacular: Mobile Phones 1940s Style

March 13, 2020 by 24 Comments

We think of the mobile phone — well, what we would call a cell phone — as something fairly modern. Many of us can still remember when using a ham radio phone patch from your parked car would have people staring and murmuring. But it turns out in the late 1940s, Bell Telephone offered Mobile Telephone Service (MTS). It was expensive and didn’t work as well as what we have now, but it did let you make or receive calls from your automobile. After the break, you can see a promotional film about MTS.

The service rolled out in St. Louis in the middle of 1946. The 80-pound radios went in the trunk with a remote handset wired to the dashboard. At first, there were only 3 channels but later Bell added 29 more to keep up with demand. An operator connected incoming and outbound calls and if three other people were using their mobile phones, you were out of luck.

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Rotary Dial Becomes USB Keyboard

November 17, 2019 by 14 Comments

[Max] had a rotary dial from an old telephone and — unsurprisingly — had nothing in particular to do with it. The simple answer? Use an Arduino Leonardo to turn it into a USB keyboard device.

Of course, the Leonardo can easily impersonate a USB keyboard, so that’s the easy part of the project. Interfacing to the dial requires an understanding of how the phone system works.

While today, TouchTone phones are most common, they were quite uncommon for many years. Early phones required you to have an operator connect your circuit to another person’s circuit. Unfortunately for the operators, the system was inherently unscalable and also cost prohibitive.

There were a variety of schemes tried and — supposedly — an undertaker who was angry that the operator was connecting his customers to her husband’s competing mortuary invented the dial telephone.

The details are pretty simple. A typical dial has two contacts. There’s a normally open contact that closes when you spin the dial to any position. It says closed until the spring returns the dial to the home position.

The other contact is normally closed and makes or breaks the phone line. Each time the dial rewinds past a position, the contact opens briefly. Of course, this is a mechanical system, so the software has to debounce the inputs, but that’s easy enough.

If you don’t have access to a dial, you could always print one. Sort of.

Retrotechtacular: The Speaking Clock Goes Silent

October 30, 2019 by 28 Comments

It used to be that time was a lot more relative than it is today. With smartphones synced to GPS and network providers’ clocks, we all pretty much have access to an authoritative current time, giving few of us today the wiggle room to explain a tardy arrival at work to an impatient boss by saying our watch is running slow.

Even when that excuse was plausible, it was a bit weak, since almost every telephone system had some sort of time service. The correct time was but a phone call away, announced at first by live operators then later by machines called speaking clocks. Most of these services had been phased out long ago, but one, the speaking clock service in Australia, sounded for the last time at the end of September.

While the decommissioned machine was just another beige box living in a telco rack, the speaking clocks that preceded it were wonderfully complex electromechanical devices, and perfect fodder for a Retrotechtacular deep-dive. Here’s a look at the Australian speaking clock known as “George” and why speaking clocks were once the highest of technology.

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Telephone Plays The Songs Of Its People

April 12, 2019 by 4 Comments

Music, food, and coding style have one thing in common: we all have our own preferences. On the other hand, there are arguably more people on this planet than there are varieties in any one of those categories, so we rarely fail to find like-minded folks sharing at least some of our taste. Well, in case your idea of a good time is calling a service hotline for some exquisite tunes, [Fuzzy Wobble] and his hold music jukebox, appropriately built into a telephone, is just your guy.

Built around an Arduino with an Adafruit Music Maker shield, [Fuzzy Wobble] uses the telephone’s keypad as input for selecting one of the predefined songs to play, and replaced the phone’s bell with a little speaker to turn it into a jukebox. For a more genuine experience, the audio is of course also routed to the handset, although the true hold music connoisseur might feel disappointed about the wide frequency range and lack of distortion the MP3s used in his example provide. Jokes aside, projects like these are a great reminder that often times, the journey really is the reward, and the end result doesn’t necessarily have to make sense for anyone to enjoy what you’re doing.

As these old-fashioned phones gradually disappear from our lives, and even the whole concept of landline telephony is virtually extinct in some parts of the world already, we can expect to see more and more new purposes for them. Case in point, this scavenger hunt puzzle solving device, or the rotary phone turned virtual assistant.

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Reverse Engineering A Telephonic Relay Device

March 23, 2019 by 20 Comments

The Plain Old Telephone Service, or POTS, doesn’t get a lot of love from the average person anymore. Perhaps once in a while a payphone will be of use when a phone battery has died, but by and large many people simply don’t have hardwired phones anymore. However, that doesn’t mean that the old landline can’t be put to good use. As [Felix Vollmer] shows us, it’s still possible to get useful hardware running over the phone line.

The YC-KZ02DN is a simple device which hooks up to a standard phone line. It’s capable of answering calls and responding to commands by switching its various relays on or off. [Felix] wasn’t quite happy with the stock functionality, however. Investigation showed the onboard STC15W202S microcontroller can be repogrammed over serial via an unpopulated header. Thus opened the door to hacking the device.

[Felix]’s alternative firmware has a couple of key features that make it valuable. Longer PINs are supported, decreasing the likelihood that malicious actors can gain access to the system. Additionally, the device is set to restore the last relay state after a power loss event. This makes the device far more useful for situations where it’s important to ensure consistent operation. It’s no use if an intermittent power loss stops your livestock’s water trough from filling, for example.

In this day and age of the Internet of Things, an old school telephony hack warms the cockles of our hearts. We’re suckers for anything that recalls the days of rotary dialing and speaking with the operator, after all.