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===== Raspberry Pi Project – A 1960s wallbox interfaced with Sonos =====
The inspiration for this project came from @nivnov pointing me to http://wallbox.weebly.com/. I had somewhat of a different take on the circuitry and software than it’s author, Steve Devlin. The pulse train of my Wallbox was also different. This is all explained below.

==== The Wallbox ====

A wallbox is a device dating from circa 1950s USA. It was placed on tables in diners to increase revenue from Jukeboxes. It contains no music, nor does it have a speaker. It could be considered a remote control for the diner’s main Jukebox.
I opted for a Seeburg Wall-O-Matic 100 Type 3W100. Wallboxes will be heavily mechanical with very basic circuitry. They will function such that a key combination will be output as a train of electrical pulses caused by an arm rotating over a set of electrical contacts.

{{:info:juke1.jpg|}}\\

==== Powering the Wallbox ====

The wallbox would have, traditionally, been powered from the jukebox. To use it standalone for this project, an AC-AC transformer was required. My Wallbox required 25VAC at a maximum of 3 amps. I used a Torodial transformer, mounted with its mounting washers, in a die-cast aluminium box. It kicks out a lot of heat so the box acts as a decent enough heatsink.
The wall boxes are traditionally unearthed. This seemed like a bad idea so I attached an earth to it via one of the unit’s screws.

{{:info:xfmr_photo2.jpg?400|}}\\

==== Interfacing with the RasPi ====

Steve’s circuit is floating and I managed to fairly impressively melt a RasPi by inadvertently forcing 25vAC through it via the gnd. In the end, I opted for a circuit that isolated the Pi from the Wallbox. A diagram is below:

{{:info:wallbox_if_schematic.png?400|}}\\