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Pulse to Tone (DTMF) converter


For use with rotary phones and VoIP adapters (ATA). e.g. Vonage, Comcast, CallCentric, Linksys PAP2T

Device should not be connected to regular POTS lines. Although it would likely work, the device has not been designed for or tested with conventional telephone lines.

The current version intercepts pulses so that digits are not sent twice.

Please report any problems you experience:

  • There is a known issue with some MagicJacks because the polarity on some versions of MagicJack is reversed from the accepted standard. This can be fixed by reversing the polarity of the RJ 11 plug which requires a crimp tool. This modification will cause the converter to not work on VoIP adapters with the correct polarity.

Plug in converter to phone line for 15 minutes before use to charge the ultra capacitor. If converter stops working, leave unplugged from phone line for at least an hour in order to discharge the ultra capacitor.

Currently, the converter is set to dial "*" after 11 pulses and "#" after 12 pulses. These are provided for those dialling pulses through a micro-controller.

"#" can also be dialled by using hook flash. On hook periods of less than half a second will cause "#" to be dialled. This can be useful when a telephone menu requires dialling "#". As a consequence, however, hook flash for features such as three way calling or call waiting must be held for longer (than 0.6 sec.) to function. (This feature was added in sw.20120302)

The core of the design is an AtMega 48 micro-controller with four BJT transistors. The tones are generated with PWM sine wave lookup on one of the counters.

BOM - Bill of Materials
  • ATMega 168
  • 8 MHz crystal
  • 2 x 2N5551 BJT transistor (new)
    • 2 x 2N3904 BJT transistor (deprecated)
  • 2 x 2N5401 BJT transistor (new)
    • 2 x 2N3906 BJT transistor (deprecated)
  • 3 x 1N4148 diode
  • 1 x 1N5231 zener diode
  • 3 x 500 ohm resistor
  • 1 x 1k ohm resistor
  • 2 x 10k ohm resistor
  • 1 x 100k ohm resistor
  • 2 x 100nF capacitor
  • 1 x 100uF capacitor
  • 1 x 330mF ultra capacitor - optional

  • Model: P2Tv2
  • 0 Units in Stock

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