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How to convert old telephones to DTMF

There is no doubt that the old retro phones of yesteryear are way more stylish than today's mass produced consumer devices. However, due to the electronics used in these old phones, they are often unsuitable for modern phone lines and cannot be used with tone based services such as Internet banking. In this article, we will look at how to convert an old phone to a modern tone based system.

Using a conversion box

Old rotary phones used a pulse system to communicate with the telephone network. This will still work with many phone networks but is simply incompatible with modern touch tone banking systems. Pulse systems work by sending out equally space pulses which correspond to the number dialed. Dialing an eight for example would result in eight pulse being sent 0.1 seconds second apart. Modern dual tone multi frequency (DTMF) systems send two simultaneous tones which can be interpreted by computer systems. The challenge presented to people who wish to use old rotary phones with modern networks and telephony systems is to change the old pulses to the modern
tone-based system. One method of achieving this is to use a pulse to tone converter such as the units which can be purchased from Oldphoneworks.com. These are simply a "black box" system which requires no technical knowledge. The phone line plugs into one socket and the telephone plugs into the other side. The disadvantage of using this solution is that the # and * keys cannot be accessed which are needed for some touch tone menu navigation systems. If you regularly use services which use these keys, then you will need to consider buying a second phone.

Full conversion

This method requires a good amount of technical competence. In order to convert an old pulse phone to touch tone DTMF, you will need a second cheap DTMF phone from which to salvage parts. Take the old pulse phone apart and remove all of the electronics. You will need to drill through the finger holes to create spaces for the buttons. It is more than likely that the buttons from the old phone will not fit the holes exactly, so you may need to shop for appropriate sized buttons from an electronics store. The buttons only have two terminals and can simply be soldered in place. As you have used the complete circuitry from a new DTMF phone, once the buttons have been installed, you can simply mount the circuit board within the case. You will find that due to modern electronic components there is plenty of space to play with. To achieve a professional finish, consider using proper PCB mounting hardware.

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