WiFi-Enabled Prop Phone

In the staged version of The 39 Steps, a ringing telephone plays an ominous role. Rather than playing a period ringtone over speakers, I modified an STC 4109B crank telephone from 1931 to enable the original bells to be rung via WiFi without any external connections.

After removing a leaky battery, powerful induction coils, and a 350v (!) capacitor, I installed an esp8622 along with two solenoids, and custom-built circuits and armature. Confining everything to the limited space of the gutted phone was a challenge, as were the custom circuits designed to provide enough power to the solenoids in a precise alternating patter without damaging the delicate circuitry of the controller.

A USB pigtail protruding from the original cord placement at the rear provides connectivity for troubleshooting and future modifications as well as the mobile phone battery pack that makes the unity truly wireless.

I cleaned up the bakelite exterior and duplicated the faceplate instructions, writing in the extension of the local venue. The result is an attractive portable prop that hopefully can be used in future productions.

Download Schematic