DTMF shield aimed at ham controlled Arduino

[Colin] wanted a way to reliably control an Arduino via ham radio. One of the easiest methods of automated radio control makes use of Dual-Tone Multi-Frequency signalling. To those who aren’t into amatuer radio you probably recognized DTMF as the touch-tone system for telephone communications. [Colin] built a shield that has an audio input and can decode DTMF signals.

The hardware is based around an MT8870 DTMF decoder chip. This is a popular choice for DTMF hardware┬ábecause it does all of the decoding work for you. Whenever a valid tone is detected it outputs the associated value in binary on four output pins. There is a fifth pin that strobes after each new tone. [Colin’s] design offers a lot of feedback for what’s going on with the input signal. The DTMF value is displayed on a 7-segment display (controlled completely in hardware), the value is output on for Binary Coded Decimal pins, and mapped to a set of ten pins which pull to ground to match the digit received.

Simple DTMF decoder pulls numbers from YouTube videos


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.

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DTMF and SelCall signal generator

[Rogal] wrote a cell phone application called ToneTool that generates audio tone sequences. It can be used to output DTMF and SelCall sequences which are used by telephone systems and radio-telecommunication hardware. The software is written in J2ME so if you have a cell phone that can run Java apps it will probably work for you. This is like a digital-age Blue-box in everyone’s pocket. But we don’t think there’s too much opportunity for the mayhem seen with the original phone phreaking.

See him generating and sending DTMF commands over an Echolink network in the video after the break.

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Easy dial telephone


[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.

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Forknife, Android G1 controlled robot


When we first saw [Jeffrey Nelson]’s G1 based robot we immediately wondered what the transport for the controls was. The G1‘s hardware supports USB On-The-Go, but it’s not implemented in Android yet. It turns out he’s actually sending commands by using DTMF tones through the headphone adapter. The audio jack is connected to a DTMF decoder that sends signals to the bot’s Arduino. He wrote client/server code in Java to issue commands to the robot. You can find that code plus a simple schematic on his site. A video of the bot is embedded below.

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