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Old 23rd Feb 2007, 12:41 pm   #5
beery's Avatar
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
Posts: 747
Default Re: Pulse (Loop Disconnect) to Tone (DTMF) Converter?

Hi Peter,
I actually made my own one to enable me to use a 300 series on my desk at work.
It did mean I had to put the circuit in the phone, but I did not have to mess around with the original workings.
I cheated by not including a bridge rectifier which has made the phone polarity sensitive, but that is ok as line reversal is not used these days.
I've included a circuit. If anyone is interested I'll have a look in my phone to see how it is connected and I'll upload the PIC code.

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