Remy van Elst Brings a Piece of Vintage Telephony Back to Life with a Simple Tone-Dialing Conversion

Despite having been made in 1965, this pulse-dialing phone can still be used — via a tone-dialing converter an a VoIP adapter.

For anyone with a tendency to keep devices beyond their expected lifespan, developer Remy van Elst has a gift: a guide to the ways in which a rotary pulse-dial telephone, like his manufactured in the mid-1960s, can be used as a Voice-over-IP (VoIP) handset.

"Recently I was gifted a T65 rotary telephone. This was the standard telephone in The Netherlands in the seventies and eighties," van Elst explains. "I remember my parents having one as well. Because this phone does not use DTMF [Dual-Tone Multi-Frequency] but pulse dialing it does not work with modern equipment, like the built in telephony/VoIP server on my FritzBox router. Using a hardware converter it is possible to convert pulse tone dialing to DTMF and to use your rotary phone again."

Readers of a certain vintage will recall the days of rotary telephones, in which numbers were laboriously dialed through the spinning of a plastic or metal disc until your finger came to rest on a stop. The rotation of the disc triggered pulses in the connection, which were decoded back into the numbers that generated them — hence "pulse dialing."

The invention of DTMF, in which push buttons allowed instantaneous entry of any number plus asterisk and octothorpe symbols, and the move to digital telephone exchanges saw pulse dialing retired — but that doesn't mean the rotary phone is dead.

With one such phone in hand, van Elst set about restoring it to working order — not as a landline receiver, in these days when many eschew such a thing, but as a handset for a Voice-over-IP (VoIP) connection. In theory, that should have been as simple as connecting it up to his existing GrandStream HT502 analog telephone adapter (ATA) — but while the H502 is supposed to support pulse-dialing equipment, van Elst found his did not. Likewise, an AVM Fritz!Box router's analog telephone connection is tone-dial only — which is where van Elst's adapters come in.

To get the phone working again, van Elst picked up a DialGizmo — a low-cost commercial dongle that accepts a pulse-dial phone and automatically converts its pulses into DTMF signals. Using this, the phone is effectively converted into pulse dialing — and operates plug-and-play with any already-configured ATA with VoIP support.

"A more homebrew project is the PicBasic 141101 pulse to tone converter," van Elst adds. "It's a small PCB that you build in to your T65 handset which provides mostly the same functionality as the DialGizmo. I decided not to buy this device due to having to mess with the internals of the T65 phone."

The full write-up is available on van Elst's website, including links to the DialGizmo and PicBasic 141101.

Main article image courtesy of

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire:
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