Generate DTMF tones only using Arduino

Dual-tone multi-frequency (DTMF) is a common signaling system used in telephone networks and other communication devices. It uses a mixture of two sine waves to generate tones which represent ten digits, the letters A to D, and the symbols # and *.

While I’m examining other Arduino based DTMF generators I noticed most of the designs are based on Holtek HT9200 DTMF generator IC. After a couple of experiments, I figure out that Arduino itself is capable enough to generate DTMF tones without using any external IC or generator.

Prototype assembly of the ladder circuit.

The design which I explained in this article is based on R-2R ladder DAC. I did this design using Arduino Uno board and still this library support only for this board. But it can easily extend to other AVR MCU based Arduino boards.

Schematic of the DTMF generator.

The R-2R ladder is attached to the PORTD of the MCU which is Digital out 0 to 7 in Arduino Uno board. In this design, I used 100Ω and 220Ω resistors to construct the R-2R ladder circuit.

In MCU, waveforms are generated using precalculated wavetable. For example, to generate a tone for digit 1, it synthesizes 700Hz (≈ 697Hz) and 1200Hz (≈ 1209Hz) waveform separately and combines at the later stages to produce the final output.

Output waveform (channel 1) compare with the analog generator.

Due to the lower resolution of the DAC, the output waveform is not in a pure sine wave shape, but it works absolutely fine with all the system which we checked.

To verify the library and DAC functionality I feed the output of this DTMF generator to MT8870 DTMF decoder and it decodes all the tones without any issues. Also, I checked this library with a voice telephone network by dialing some numbers and it also works fine.

The Arduino library for this DTMF generator is quite easy to use. By using this library you can generate DTMF tones for any digit or for symbols # and *.

The library and source code of this project are available at https://github.com/dilshan/dtmfgen.

Comments

CD2003 - yet another simple FM radio receiver

In the last few days, we are looking for some simple FM radio receiver to integrate into one of our ongoing projects. For that, we try several FM radio receiver ICs including TDA7000, CD2003/TA2003/TA8164, CXA1019, and KA22429. Out of all those chips we select CD2003 (or TA2003/TA8164) based receiver for our project because of its simplicity and outstanding performance. Except to CD2003, Sony CXA1019 also perform well but we drop it because of its higher component count. We design our receiver based on Toshiba TA2003 datasheet and later we try TA8164 and CD2003 with the same circuit. Either CD2003 or TA8164 can directly replace TA2003 IC, and as per our observations, TA8164 gives excellent results out of those 3 chips. A prototype version of CD2003 FM radio receiver The PCB design and schematic which we used in our prototype project are available to download at google drive (including pin-outs of crystal filters and inductors ). Except for CD2003 IC, this receiver consist...

Arduino superheterodyne receiver

In this project, we extend the shortwave superheterodyne receiver we developed a few years ago . Like the previous design, this receiver operates on the traditional superheterodyne principle. In this upgrade, we enhanced the local oscillator with Si5351 clock generator module and Arduino control circuit. Compared to the old design, this new receiver uses an improved version of an intermediate frequency amplifier with 3 I.F transformers. In this new design, we divide this receiver into several blocks, which include, mixer with a detector, a local oscillator, and an I.F amplifier. The I.F amplifier builds into one PCB. The filter stage, mixer, and detector stages place in another PCB. Prototype version of 455kHz I.F amplifier. In this prototype build, the Si5351 clock generator drives using an Arduino Uno board. With the given sketch, the user can tune and switch the shortwave meter bands using a rotary encoder. The supplied sketch support clock generation from 5205kHz (tuner f...

Calculator for audio output transformers

Audio output transformers are heavily used in a vacuum tube and some (older) transistor base audio power amplifiers, but these days output transformer are quite hard to find and expensive item. For homebrew projects, the best option is to construct those transformers by ourselves and this script helps to calculate winding parameters for those transformers. This " AF output transformer calculator " script is written using Python and it works with most of the commonly available Python interpreters . The script is available to download at google drive under the terms of GNU General Public License version 3.0 . Homebrewed 25k: 4 output transformer Once supplied the input parameters this script provides a winding ratio, the number of turns required for primary and secondary winding and required copper wire gauges for both primary and secondary windings, etc. We construct several AF output transformers based on results of this script, which including transformers for M...