Re: British Telecom C2 klaxon and control box
It hoots twice, same as an ordinary ringer, then it misses out the next pair of rings, and hoots twice for the next pair.
A 'loaded' relay would be one way to do it.
Any ideas about how the GPO did it? I was always curious to find out what the ringer in the actual telephone instrument did, but I never manage to be in the office when it rang.
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