Telephone pulse to DTMF converter
Description:
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.
Update: 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 https://itunes.apple.com/us/app/dtmf-dial/id439867878?mt=8
Update: Good news head over our Telephone pulse to DTMF converter MKII for a working version of the circuit.
Picture gallery:
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The pulse to DTMF converter connected to the telephone. I decided to place the pcb in a shrinkable tubing and holding this in place inside the telephone with cable ties (I have not taken any picture of this). The wiring is shown in the schematic, but be very careful as you risk to destroy your IP telephone adapter, and NEVER connect a telephone with my pulse to DTMF converter to the PSTN telephone system, it is illegal.