On his blog, [Kenneth Finnegan] recently showed off a replica of a fun toy he used to play with as a kid, a telephone intercom system. The setup is pretty simple, requiring little more than a pair of analog phones, a battery, and a resistor.

The phones are connected to one another using a standard telephone cable, but [Kenneth] uses a 9v battery to introduce a small bias current into the loop, allowing the speakers at either end to hear one another. He also added a small LED into the circuit so that there is a visual indication as to when both handsets are off hook.

The setup is very simple at the moment, though [Kenneth] does have some ideas in mind to enhance his intercom system. He hopes to tweak the remote phone to ring when the local phone is picked up, among other things.

Telephone technology is nothing new, but for just a few dollars (or less) your kids can be entertained for hours as [Kenneth] was way back when.

Continue reading to see a short video overview of the phone system, and be sure to share your ideas for enhancing it in the comments section.

If you’ve ever wondered about the best way to detect dial and DTMF tones from a phone line, [Debraj] is your man.

[Debraj] built a DTMF detector using the Goertzel algorithm. Normally, when we think about detecting tones, we pull FFT out of our bag of tricks. The Goertzel algorithm isn’t as computationally complex as FFT and can be implemented on even the smallest microcontrollers.

For the build, the first thing to solder is a nice audio transformer and some protection diodes. The ring tone from a phone line goes from +35 V to -35 V – a bit more than a microcontroller could handle. A PIC18F4520 dev board was used as the brain of the system with all the code is available on [Debraj]‘s site.

Although implementations of the Goertzel algorithm are a little uncommon, [Debraj] has seen a few interesting projects using this technique. [Debraj]‘s build could easily be modified into a guitar tuner with a few changes in the code, for example.

This project was built as the command and control for a home automation system and from the video after the break, we can’t wait for [Debraj] to get annoyed at the phrase, “To turn on the kitchen lights, please press 1…”

[Victor's] girlfriend works at a museum and enlisted his expertise in designing an interactive detective game for kids visiting the museum. The vision was for the kids to discover phone numbers that they could call for clues. Originally he planned to display the clues on a character LCD, but obviously it’s much neater to hear the clues in the handset of the phone.

Quickly switching gears, [Victor] dropped the ATtiny2313 and started over with an Xmega chip — in fact, it was our recent Xmega post that inspired him to document his project. The microcontroller is responsible for a lot of goings-on. It scans the key matrix for inputs, simulates the DTMF touch tones, reads audio files from a FAT file system on an SD card, and plays them back over the hand set’s speaker. Since most of the hardware is already built into the phones, it was not hard to fit his add-ons inside the case. A simple audio amplifier circuit joins the microcontroller, which is patched into the rows and columns of the keyboard. Take a gander at the video after the break to see the device in action.

While many of us have banished land line telephones from our houses, there are still quite a few people who utilize POTS lines today. These analog phone systems use Dual Tone Multi Frequency (DTMF) signals in order to audibly represent all of the keys on a telephone keypad and place calls. [Brad] over at LucidScience decided that it would be useful to have a DTMF decoder on hand, and got busy building one.

His DTMF decoder box uses a CM8870 DTMF decoder chip, which you might assume is all you need to get the job done. This chip performs its duties very well, outputting a 4-bit binary code for each button press it registers, but that doesn’t do a whole lot of good without being able to represent those codes in a meaningful fashion. He first built a breadboard decoder circuit that would light 1 of 16 LEDs depending on the detected button press. This was well and good, but he decided that an Arduino-driven LCD display would work far better.

When he was finished, he had a compact decoder box with an LCD display, which accepts input from either an RJ-11 cable or an audio jack. He says that the audio jack is particularly useful for decoding tones from computer audio, such as YouTube clips. [Brad] praises the CM8870 chip, stating that it can pull phone numbers from pretty much any audio or phone signal you throw at it, regardless of quality. We think it would make a great basis for a telephone-based security system, if that was something that appealed to you.

Be sure to stick around to see his DTMF decoder circuit in action.

[Headsheez] found a way to get his home phone service for free. He’s using a set of tools that we’re familiar with to route service from a typical analog phone system (which involves the extensions wired into your home) through a server to the Internet. On the hardware side of things this starts out with an Analog Telephone Adapter which translates the analog signal for use in a PBX system. He uses a copy of the open source PBX project called Asterisk which we’ve also seen used on devices like routers and the SheevaPlug. The actual telephone number comes from a Google voice account which for now is a free service but there’s no guarantee that it will remain that way in the future.

This should provide seamless service just like you’re used to with a traditional home phone line. There’s even caller ID for the number – but not the name – for incoming calls. The one big feature that is missing from this setup is the ability to call 911 for emergencies.

[via Reddit]

[Itay] has a friend who works in a rented office where the parking lot is secured by a remote-controlled gate. Unfortunately, while his friend shares an office with several people, they only received a single remote. To help his friends out, he built a small device that triggers the remote control whenever a phone call is received.

The remote modification was rather straightforward. He simply opened the device, adding a single wire to each button terminal. Rather than connect to the remote using wires, he decided to fit it with what looks like a scavenged DC power jack. The ring detector circuitry was constructed and stuffed in a small phone box, which is connected to the remote using a DC power plug. It’s a great solution to the problem, but let’s just hope no one gets a hold of the phone number they used for the trigger!

There are plenty of pictures on his site, as well as video of the ring detector being tested. Unfortunately [Itay] lost the original schematics for the circuit, so you will have to flesh that part out on your own if you wish to build a similar device.

Keep reading to see a few videos of the remote in testing and in use.

[Matt] brought together a TV remote and cordless phone to add a locator system to the remote control. One of the best features of a cordless phone is the pager button on the base. When you press it the handset beeps until found. Matt gutted one and got rid of the unnecessary parts. He then cracked open his TV remote housing and inserted the telephone handset’s circuit board, speaker, and battery. The base station is used just like normal to locate the phone/remote combo, and has been modified with a charging cable to top-off the telephone battery which powers everything in the newly hacked unit. [Matt's] demonstration video is embedded after the break.

It’s too bad that he got rid of the microphone. It would be interesting to take calls on this thing.

[James Bond] types and those suffering from a hefty dose of paranoia can now record all telephone conversations. [Trax] built this module that monitors the phone line and starts recording when a handset is picked up. A computer does the actual recording, triggered by the microcontroller via a USB connection.

We like the use of an old PCB for a faceplate, we’ve certainly got some duds of our own sitting around. The three cords are a bit confusing though. One for the phone line, one for the USB, but what does the third do? Is it an audio-out connection?

We’ve asked [Trax] to post a schematic and source code if possible so that might clear up the mystery.

Update: [Trax] let us know that there is a red button with white lettering at the bottom labeled “download”. This contains schematic, code, pcb layout, and PC software. We just missed it the first time around.

While visiting family we noticed that their telephone had a dedicated GOOG-411 button. We’ve been using Google’s free 411 service for what seems like years but seeing this show up in the form of an auto-dial button is astonishing.

The question that pops to mind: how is this not an antitrust suit waiting to happen? Directory assistance is BIG MONEY that Google undercut when launching its free service. By shipping phones that have the number pre-programmed doesn’t that limit choice and competition in the same way that shipping Windows with Internet Explorer does? Perhaps the difference is that Microsoft has a near monopoly on the PC OS market while GE can’t say the same about cordless phones.

We’re not antitrust lawyers, and neither are you, but we’d still like to hear your opinions about this in the comments.

Cramming Bluetooth headset circuitry into an analog telephone body has become an extremely popular hack. With declines in the prices of these headsets, and older telephones being seen as storage-room-clutter this hack is just waiting for you to get started. Join us after the break for a look at what others have already accomplished.

Traditional:

The most common Bluetooth handset hack involves standard receivers. This is because they are relatively comfortable to hold and readily available. Chances are someone you know will give you an old phone for free if you just ask. Some of the important things to remember when sandwiching a Bluetooth headset into an old school handset is how to handle the buttons and how to charge the device. Some of these examples have routed the buttons and connector into the case of the phone, others just require the removal of the microphone cap for recharging. There’s no doubt that receivers #1, #2, #3, and #4 all achieve the desired retro look.

Unorthodox:

We’ve covered both of these hacks before. The whimsical iGiveUp handgun handset is a social disaster waiting to happen. But if you don’t mind court-mandated counseling give it a try yourself. For those who want a phone that can be used at the airport, the NES set is a safe bet and has the added bonus of allowing you to carry around an old school controller.

True Vintage:

We were quite surprised that we didn’t find more hacks that involve some really old phones. Then again, these are antiques that most would not dream of cracking open. This candlestick phone looks great, but we image it’s not as comfortable to use as the more common receivers we saw earlier.

Steam Punk:

These aren’t handsets and one of them doesn’t have any electronics in it at all! But we couldn’t finish this roundup without a mention of the Steam Punk styled Bluetooth headset. The earpiece on the right is a piece of jewelry by designer [Chris Cobalt]. Truthfully, we’re kind of sick of seeing people wearing ugly plastic headsets everywhere they go. Make a statement and use [Chris'] design as inspiration to customize your dongle.

Commercial:

Handset hacks turned out to be so popular that they’ve started to pop up on the commercial market. Above are two of the better renditions. On the left is a rotary phone model from SparkFun. To the right are two examples of Think Geek’s offering. There’s plenty more out there on eBay and the like, but don’t you want to be able to say “actually, I made it” when people ask where you got your geeky peripheral?

[Taufeeq's] Grandmother needed to be able to call her family members but due to ailing eyesight and memory this was a difficult task. He decided to help her with this by building a telephone that will auto-dial a number at the push of a button. [Taufeeq] built a case to hang on the wall which houses a hook for the receiver and two auto-dial buttons. The buttons are lighted and loosely based on the LED push buttons we covered in January. Housed in a separate box are a microcontroller and a dual tone multiple frequency IC used to dial the numbers. These are patched into a PCB from a standard telephone.

The result looks great and makes using the phone much easier with the simplified controls. We’ve included the demonstration video after the break.

We’re starting to think that phone numbers are deprecated; it may be time to integrate how we connect telephones with the new digital millennium. To get a firm grasp on this topic it is important to take a look at the reason we started using phone numbers, why we still use them, and the why’s and how’s of transitioning to a new system.

History of phone numbers

Telephone numbers started out as a way of physically addressing a telephone extension. Whether connected by an operator at a switchboard or through a magnetic exchange, each number corresponded to the hardware switch that connected the handset you were trying to ring. This originally started with named exchanges such as Pennsylvania-6-5000. The geographic location of the extension was  shown in the name and this system gradually transitioned over to area codes and prefixes.

Continued usage

The proliferation of cell phones means that numbers are no longer tied to a physical location but are routed to the nearest tower to which each wireless phone is currently connected. So why have we continued to use telephone numbers? Backwards compatibility is paramount. Cell phones overtook land lines years ago but there are still millions of people connected to the telephone companies’ wired networks. Most of the phones used on these land lines rely on the touch tone system to function. Even the advent of Voice over Internet Protocol implements the same system of connecting calls by dialing a number.

What works better than phone numbers?

How many different phone numbers does your family have? Many households have a home phone, a cell phone for each family member, and a work phone for each adult. What if all of these numbers were addressed similarly to how the Domain Name System works for internet addresses? Something like this:

phone://famiy.johndoe2155.voice/john_at_home

phone://family.johndoe2155.voice/jane_at_home

phone://www.your_company’s_domain.com/customer_service

This can be accomplished in the near future. All cell phones and many land line phones already have the ability to store numbers so that you only have to enter them once. Cell phones can already input web-style addresses and a firmware upgrade would allow for a new system of addressing and storing voice connection information. Service providers like Comcast and Charter are already providing phone service that utilizes VOIP, paving the way for dialing from your computer. For legacy hardware an inexpensive interface box similar to the digital cable converter boxes could be implemented. The new box would have a keyboard and character LCD and be rolled out in the same way that caller ID boxes were.

Conclusion

No one wants to change their telephone number and be in the position of trying to inform everyone who might ever call them. This is why laws were enacted to allow you to keep your telephone number if you change carriers. If each family owned their “voice domain”, changing carriers, cities, or even countries would be as simple as editing the domain registration. Transitioning to a new system of dynamically addressed telephone extensions is the next logical step in voice communications. Although it would be a change for billions of people, it is possible and worth taking a look at.

[photo credit Projekt Runeberg]

Starfish PBX takes the very popular Asterisk telephony platform and adds an open source, fully functional web management interface. Asterisk allows you to be your own private branch exchange; think of it as your own telephone company. You can setup extensions in your home or office, configure an intercom system, implement a hold system with music, manage voice mail, and integrate Voice over Internet Protocol. Starfish PBX, available in alpha release today, aims to make Asterisk available to a wider user base by simplifying the interface used to setup and maintain the system.

[via Digg]

[Jason Scott] curated a nice collection of links related to [Phil Lapsley]‘s work on phone phreaking. [Lapsley]‘s book, The History of Phone Phreaking, will be released in 2009. Meanwhile phone phreak enthusiasts can peruse his site and bone up on some interesting material, including documents that revealed the inner workings of the telephone switchboard(PDF), and the Youth International Party Line (YIPL)/Technological American Party (TAP) FBI files(PDF), which is really intriguing for the various doodles and conversations that were documented. If you have some spare time, we definitely recommend sifting through it.

[via Waxy]