Telephone pulse to DTMF converter


During a visit to the local recycling station, I stumbled over an old GNT-A F68 telephone, and it was a bargain I could not say no to. When I connected the telephone to my Sipura SPA 2102 IP telephone adapted, I realized that I could not make any calls from the telephone as it dials through pulse and my adapter only accepts DTMF.
Surfing the web I found a design similar to the one below but for a Dutch T65 telephone and this model is somewhat different than my GNT-A F68. I then discussed the matter with my brother and we decided to try to make our own version for my GNT-A F68.

We do not offer any support for this project anymore! Our best advice is to get a DTMF dialer app for your smartphone e.g. DTMF dial

Update: Good news head over our Telephone pulse to DTMF converter MKII for a working version of the circuit.

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