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Validating the prototype

A project log for Pulse to Tone Converter

Converts pulse dialing of your POTS telephone to DTMF dialing allowing you to use it with your VOIP's FXS-port.

Christoph TackChristoph Tack 03/17/2018 at 21:040 Comments

Printed board assembly

Assembly is fairly easy.  Be careful buying the BAT46W in the correct package.  I've updated the PCB to revision /1, replacing the BAT46WJ (SOD-323) to BAT46WH (SOD-123).  The -WH variant is bigger and easier to solder by hand.

Programming the board

I explained the procedure already in a previous log.  To connect the programmer to your ATTINY85, you can use a Pomona SOIC-clip as shown on the image below.

Measuring interrupt frequency

To check if the crystal has the correct load capacitors attached.  A special debug firmware is loaded into the device which generates a square wave with a frequency that should be 31.250KHz.

Interrupt frequency should be 31.250KHz

Mounting in the housing

The housing originally contained an ADSL-splitter.  It can be bought for a few cents from AliExpress.  Its PCB has been removed.  The modular jacks have been transferred to the pulse-dtmf-converter.

Pulse-dtmf-converter in its opened housing.
The PCB that was originally mounted is shown below it.

Finishing up

The Philps DECT-phone, which uses tone dialing is connected to the "PHONE"-port of the converter, as indicated on the bottom of the housing.

The FXS-port of the internet gateway is connected to the "MODEM"-port.

The pulse dialing phone is connected to the "LINE"-port.

Pulse-dtmf-converter in use...

Making a few test calls assured me that both phones are working well.


That's all, folks.

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