[poprhythm]’s Touch Tone MIDI Phone is a fantastic conversion of an old touch tone phone into a MIDI instrument complete with intact microphone, but this project isn’t just about showing off the result. [poprhythm] details everything about how he interfaced to the keypad, how he used that with an Arduino to create a working MIDI interface, and exactly how he decided — musically speaking — what each button should do. The LEDs on the phone are even repurposed to blink happily depending on what is going on, which is a nice touch.
Of course, it doesn’t end there. [poprhythm] also makes use of the microphone in the phone’s handset. Since the phone is now a MIDI instrument with both a microphone and note inputs, it’s possible to use them together as the inputs to vocoder software, which he demonstrates by covering Around the World by Daft Punk (video).
We love how [poprhythm] explains how he interfaced to everything because hardware work is all about such details, and finding the right resources. Here’s the GitHub repository for the Arduino code and a few links to other resources.
Some guys get all the breaks. [Guy Dupont] had the honor of building a working, interactive wall-mount landline phone for the red carpet premiere of a certain TV show. The phone was to be an Easter egg inside an 80s-style pizzeria set. About every two minutes the phone would ring, and anyone brave enough to answer would be greeted with either a fake pizza order, an old answering machine message, or a clip from The Show That Cannot Be Mentioned.
So the phone doesn’t work-work, but the nostalgia is strong — picking up the receiver when the phone isn’t ringing results in a dial tone, and button pushing leads to the busy signal. Those old pleasant-but-stern operator recordings would have been cool, but there was only so much time. (Your call cannot be completed as dialed. Please check the number and try again.)
[Guy] used a SparkFun RP2040 to handle input from the DTMF keypad and play the tones, the dial and busy signals, and the various recordings into the ear of the receiver.
Instead of messing around with the high voltage needed to drive the original ringer and bell, [Guy] used a small speaker to play the ringing sound. Everything runs on eight AAs tucked under the keypad, which is stepped down to 5 V.
This project was built under fairly dramatic duress, which makes it that much more exciting to watch the build video after the break. With just five days to get the phone working and in the mail, [Guy] holed up on the floor of his office, his messy mid-move refuge from a house plagued by COVID. Unfortunately, the whole pizzeria thing fell through, so [Guy]’s phone will not get to have its moment on the red carpet. But at least it’s on the site that’s black and white and read all over.
Though many of us will never have experimented with it, most readers should be familiar with DTMF as the tones used by the telephone system for dialling. If your youth was not misspent mashing 4-4-2-6-4-6-2, 4-4-2-6-4-1 into a keypad, then you haven’t lived!
As you might expect there are a variety of chipsets to handle DTMF, and one of them has been used by [ackerman] in a slightly unusual way. Many desktop computers do not have a convenient array of GPIOs upon which to hang a piece of hardware, but a constant among them is to support some form of gaming controller. Hence he’s taken a commodity joypad and interfaced a MT8870 DTMF decoder to its switch lines with a simple transistor buffer, and is able to pull the resulting information out in the host operating system. So far there are versions for Windows, DOS, Amstrad CPC, Arduino, and even PSX ( the original PlayStation console ).
One might ask why on earth you might want a DTMF input for your desktop PC, but to do so is to miss the point. We are surrounded by computing devices from our mobile phones upwards that do not have any form of interface that can easily be used by our electronic projects, and this serves as an example of how with a bit of ingenuity that can be overcome. It’s a subject we’ve touched upon before, when we asked why people aren’t hacking their cellphones.
Right up front, let us stipulate that we are not making fun of this project. Even its maker admits that it has no practical purpose. But this 3D-printed Commodore-style rotary dial keypad fails to be practical on so many levels that it’s worth celebrating.
And indeed, celebrating deprecated technology appears to be what [Jan Derogee] had in mind with this build. Rotary dials were not long ago the only way to place a call, and the last time we checked, pulse dialing was still supported by some telephone central office switchgear. Which brings us to the first failure: with millions of rotary dial phones available, why build one from scratch? [Jan] chalks it up to respect for the old tech, but in any case, the 3D-printed dial is a pretty good replica of the real thing. Granted, no real dial used a servo motor to return the dial to the resting state, but the 3D-printed springs [Jan] tried all returned the dial instantly, instead of the stately spin back that resulted in 10 pulses per second. And why this has been done up VIC-20 style and used as a keypad for Commodore computers? Beats us. It had to be used for something. That the software for the C-64 generates DTMF tones corresponding to the number dialed only adds to the wonderful weirdness of this. Check out the video below.
For a hobby that’s ostensibly all about reaching out to touch someone, ham radio can often be a lonely activity. Lots of hams build and experiment with radio gear much more than they’re actually on the air, improving their equipment iteratively. The build-test-tweak-repeat cycle can get a little tedious, though, especially when you’re trying to assess signal strength and range and can’t find anyone to give you a report.
To close the loop on field testing, [WhiskeyTangoHotel] threw together a simple ham radio field confirmation unit that’s pretty slick. It relies on the fact that almost every ham radio designed for field use incorporates a DTMF encoder in the microphone or in the transceiver itself. Hams have used Touch Tones for in-band signaling control of their repeaters for decades, and even as newer digital control methods have been introduced, good old analog DTMF hangs in there. The device consists of a DTMF decoder attached to the headphone jack of a cheap handy talkie. When a DTMF tone is received, a NodeMCU connected to the decoder calls an IFTTT job to echo the key to [WTH]’s phone as an SMS message. That makes it easy to drive around and test whether his mobile rig is getting out. And since the receiver side is so portable, there’s a lot of flexibility in how tests can be arranged.
On the fence about ham as a hobby? We don’t blame you. But fun projects like this are the perfect excuse to go get licensed and start experimenting.
There are many viable options for home security systems, but where is the fun in watching a static camera feed from inside your place? The freedom to really look around might have been what compelled [Varun Kumar] to build a security car robot to drive around his place and make sure all is in order.
Aimed at cost-effectiveness and WiFi or internet accessibility, an Android smartphone provides the foundation of this build — skipping the need for a separate Bluetooth or WiFi module — and backed up by an Arduino Uno, an L298 motor controller, and two geared DC motors powering the wheels.
Further taking advantage of the phone’s functionality, the robot is controlled by DTMF tones. Using the app DTMF Tone Generator and outputting through the 3.5mm jack, commands are interpreted by a MT8870DE DTMF decoder module.While this control method carries some risks — as with many IoT-like devices — [Kumar] has circumvented one of DTMF’s vulnerabilities by adding a PIN before the security car will accept any commands.
He obtains a live video feed from the phone using AirDroid in concert with VNC server, and assisted by a servo motor for the phone is enabled to sweep left and right for a better look. A VNC client on [Kumar]’s laptop is able to access the video feed and issue commands. Check it out in action after the break!
One late night many decades ago, I chanced upon a technical description of the Touch-Tone system. The book I was reading had an explanation of how each key on a telephone sends a combination of two tones down the wire, and what’s more, it listed the seven audio frequencies needed for the standard 12-key dial pad. I gazed over at my Commodore 64, and inspiration hit — if I can use two of the C64’s three audio channels to generate the dual tones, I bet I can dial the phone! I sprang out of bed and started pecking out a Basic program, and in the wee hours I finally had it generating the recognizable Touch-Tones of my girlfriend’s phone number. I held the mouthpiece of my phone handset up to the speaker of my monitor, started the program, and put the receiver to my ear to hear her phone ringing! Her parents were none too impressed with my accomplishment since it came at 4:00 AM, but I was pretty jazzed about it.
Since that fateful night I’ve always wondered about how the Touch-Tone system worked, and in delving into the topic I discovered that it’s part of a much broader field of control technology called in-band signaling, or the use of audible or sub-audible signals to control an audio or video transmission. It’s pretty interesting stuff, even when it’s not used to inadvertently prank call someone in the middle of the night. Continue reading “In-Band Signaling: Dual-Tone Multifrequency Dialing”→