Automatic Phone Dialer Illuminates Inner Workings

The invention of the transistor ushered in a lot of technologies that we now take for granted, and one of the less-thought-about areas that it improved living conditions worldwide was by making the touch-tone phone possible. No longer would the world have to fuss with dials to make phone calls, they could simply push some buttons. This technology is still in use today, and it is possible to build external phone dialers that use these tones to make phone calls, as [SunFounder] demonstrates with his latest project.

The tones that a phone makes when a button is pressed correlate with specific frequencies for each number. Automatic dialers like this one help when there are multiple carriers (like different long-distance carriers, for example) where different prefixes can be used to make calls cheaper depending on the destination of the call. A preprogrammed dialer can take all of this complication out of making phone calls. [SunFounder] is able to make a simple dialer from scratch, using an Arduino, its “tone” library, and a speaker that is simply held up to the phone that the call will be placed on.

[SunFounder] points out that he built this more because he’s interested in the inner workings of phones, and not because he needed a purpose-built dialer. It’s a good demonstration of how phones continue to use DTMF though, and how easy it is to interface with such a system. It might also suit a beginner as an introduction to the world of phreaking.

Twilio adds touch tone telephone control for Arduino

An Arduino with an Ethernet shield, nothing new right? Not quite, [Chris] is showing us how to use Twilio to control an Arduino via a touch tone telephone. We saw Twilio used before in a cellphone video game but this time around an audio menu system comes into play. You can make your own menus whose options will be read by the WOPR (see the demo after the break) when you call the Twilio number. This application just turns an LED on and off but once you’ve got access to the Arduino the sky’s the limit. Most immediately this is an easy implementation for all those cellphone door lock systems we’ve seen. We also envision some classic home automation such as feed the cats or turn on the lights.

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