Rotary Phone MIDI controller still calling

[Kevin] For a long time wanted to do something musical with a vintage rotary phone and an Arduino, and finally did it, running the first of several experiments with HTML in a five-part series. He found a nice old British Telecom number, but it had been converted to plug-and-socket wiring to work on the modern system. Because of this, [Kevin] wanted to keep it fully functional as a phone. After all, it should work well until 2025, when pulse dialing is no longer supported in [Kevin]’s place.

As you can probably understand, [Kevin] wanted to communicate with the phone from the outside and leave the inside untouched. He used the PCB from a sacrificial ADSL filter to break the socket and added a pull-up resistor between the pin and 5 V.

Fairly quickly, [Kevin] found out that when the phone is on hook it gives a constant high signal while picking up the phone is a high signal going low and dialing each number results in pulses of that amount alternating high and low .

In part two of the series, [Kevin] really gets to work decoding the pulse dialing, which is needed for the third episode when things get musical. Here, [Kevin] adds a MIDI module and a Roland MT-32 synth to use the dial as a MIDI note generator – each note chosen is retained until the receiver is placed back on the hook.

Part four focuses on a MIDI patch changer. [Kevin] picks up the phone, dials a code up to three digits long, and hangs up, giving the synth the assigned voice. In part five, the phone becomes a random note sequencer, and each subsequent turn of the same number will produce a different, randomly chosen note. However, this is just the beginning, so we’ll be checking back regularly for updates. In the meantime, you can listen to the note generator and random note sequencer demos after the break.

Wouldn’t you always like to use a rotary knob? As long as it wasn’t an emergency?

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