My vintage Strowger Telephone Exchange Demonstrator

This video captures the fundamentals of a step-by-step or Strowger telephone exchange. This was the global standard for almost 100 years.
I have reconstructed two small exchanges. One of these is a demonstrator  that allows two telephones to dial a number and connect to the other telephone. It has two subscriber circuits and one final selector. My other mini Strowger exchange connects four telephones. This exchange has two group selectors and two final selectors. The first caller uses the primary group and final selectors. When the line is busy the next caller will be diverted to the secondary selectors.
For tone generation (dial tone, ring tone and occupied tone) I can either use an Arduino microcontroller or a genuine dynamotor. In the picture I have removed the cover of the camshaft that controls the intermittent tone sequencing. The tones themselves and the 75V ringer signal are produced by an AC generator with special windings. The AC generator is connected to a 50V DC motor.
For other vintage telecommunication stuff see my website:
wimsmuseum.jouwweb.nl