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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

Adjusting DTMF-amplitude

Someone reported that the DTMF-amplitude was too large for their application.  Increasing R10 from 10K to 100K and R12 from 10K to 15K fixed that.

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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