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

January 14, 2023 by Dan Maloney 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.

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A laptop with a desk phone and a 3D-printed acoustic coupler next to it

Acoustic Coupler Gets You Online Through Any Desk Phone

December 30, 2022 by Robin Kearey 48 Comments

Up until the mid-1980s, connecting a computer to a phone line was tricky: many phone companies didn’t allow the connection of unlicensed equipment to their network, and even if they did, you might still find yourself blocked by a lack of standardized connectors. A simple workaround for all this was an acoustic coupler, a device that played your modem’s sounds directly into a phone’s receiver without any electrical connection. Modem speeds were slow anyway, so the limited bandwidth inherent in such a system was not much of a problem.

Nowadays it’s easier to find an internet connection than a phone line in many places, but if you’re stuck in an ancient hotel in the middle of nowhere you might just find [GusGorman]’s modern take on the acoustic coupler useful. The basic design is quite simple: it’s a 3D-printed box with two cups that fit a typical phone handset and a space to put a USB speaker and microphone. Thanks to minimodem it’s easy to set up a connection with any other computer equipped with a phone connection.

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Virtualizing IPhoneOS 1.0

December 25, 2022 by Al Williams 3 Comments

Virtualizing computers is nothing new. However, Apple devices always present challenges. Just ask anyone who has built a Hackintosh. At least computer hardware is usually exposed, but on phones, the challenge is even harder due to mysterious devices. [Martijn] managed to reverse engineer the iPod Touch 1G enough to run iPhoneOS 1.0 on it and has several blog posts explaining how he did it.

The emulator is the ubiquitous QEMU. He has emulation for the critical hardware, including the cryptographic modules, the hardware clock, and the timer, along with memory and display and interface hardware. However, Wifi, some USB, audio, the light sensor, and some graphics hardware are still absent. That doesn’t stop the OS from booting, however.

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Stack Trace From The 1950s Punches Again

December 2, 2022 by Chris Lott 4 Comments

This repair/tutorial video by the telephone Connections Museum of Seattle features an amazing piece of electro-mechanical technology from the 1950s — the 5XB trouble recorder. Museum volunteer Sarah the “Switch Witch” has a deep passion for old phone equipment, and gives an excellent description of the trouble recorder, the problems it solved, and how it works, and how they went about fixing it.

As central office switching became more complex and more dense, the manual methods of hunting down faults became unmanageable. Semi-automatic approaches using trouble lamps, but even that had its limits. This “stack trace”, which could have hundreds of indicators, had to be frozen while the technician recorded the status on a form. If another fault came along during this time, it was lost. The solution, using the available technology of the day, was a mind-boggling punched card apparatus that punches over a thousand bits of information when an switching error is detected or when various watchdog timers expire.

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Two landline phones connected to a set of wires and boards

How To Build Your Own Analog Phone Network

November 23, 2022 by Robin Kearey 18 Comments

Analog phones may be nearly obsolete today, but having served humanity for well over a century they’re quite likely to pop up in drawers or attics now and then. If you’ve got a few of them lying around and you think it’d be cool to hook them up and make your own local telephone system, check out [Gadget Reboot]’s latest work. His video series shows all the steps towards making a fully-functional wired phone system.

Of course, dedicated phone exchanges for home or small business use are not hard to find, but [Gadget Reboot] decided it would be way more interesting to design his own system from the ground up. To begin with, he used off-the-shelf subscriber line interface circuits (SLICs) to implement the correct voltages, currents and impedances to drive analog phones. He then added a DTMF decoder chip to allow the phone to dial a number, and hooked up both systems to an ESP8266 which controls the entire system. It implements the different states of picking up, dialing, ringing and hanging up, and also generates the corresponding audio signals.

The system becomes even more interesting through the implementation of a multi-exchange layout, just like in large-scale phone systems: when a number is dialled that’s connected to a different exchange, then a connection must be made between two exchanges in order to complete the call. Large-scale systems use dedicated protocols like SS7, but [Gadget Reboot] preferred to keep things simple and used an RS-485 connection. The two ESPs check each others status and if everything’s in order, a relay connects the two lines and the circuit is completed.

The current system is a bit of a mess of wires, but it works, and [Gadget Reboot] plans to make a cleaner setup based on custom circuit boards, possibly expanding it with functions like modem support. In any case it’s already way more advanced than a simple electromechanical system. Want to know more about classic phone networks? We’ve got you covered.

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Will The Fax Machine Ever Stop Singing?

November 16, 2022 by Kristina Panos 43 Comments

Throughout the 80s and 90s, you couldn’t swing a stapler around any size office without hitting a fax machine. But what is it about the fax machine that makes it the subject of so much derision? Is it the beep-boops? The junk faxes? Or do they just seem horribly outdated in the world of cloud storage and thumb drives? Perhaps all of the above is true. While I may be Hackaday’s resident old school office worker et cetera, it may surprise you to learn that I don’t have a fax machine. In fact, the last time I had to fax something, I recall having to give my email address to some website in order to send a single fax for free.

Over across the pond, the UK government has decided to nix the requirement for fax services under something called the Universal Service Order (USO) legislation, which essentially ensures that residents all across the UK have access to phone services at a price they can afford. The UK’s Office of Communications, aka Ofcom, have announced recently that they are in agreement with the government. Since the industry is moving away from the public switched telephone network (PSTN) to IP telephony, the fax machine won’t work the same way.

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PSU charging an externally connected supercapacitor bank that's powering the phone. There's a current clamp on one of the wires to measure charging current, and a multimeter measuring the charging voltage.

Just How Fast Could You Charge An IPhone?

November 3, 2022 by Arya Voronova 23 Comments

An iPhone 8, now a relatively cheap model, can charge its battery fully in two hours’ time. There’s hardly ever a need for faster charging, but it’s fair to ask – how much faster could it really go? [Scotty Allen] from [Strange Parts], back after a hiatus, is back to stretching the limits of what a regular iPhone can do, and decides to start off with an exploration of battery technologies.

What people commonly encounter is that charging speed depends on the charger involved, but even one hundred chargers in parallel won’t speed up this iPhone’s charging rate, so what’s up? First off, the phone’s charger chip and the battery’s BMS will both limit charging current, so for experiment purposes, those had to be bypassed. First attempt was using a hefty DC power supply with the original cell, and, unsatisfied with the lack of fire and still relatively slow charging, [Scotty] decides to up the ante.
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