4 ms·

How did they know when the next hour started without digital communication?

• jcrawfordor 4y ago
  The details depended on the system. The most common arrangements were either polarity (hour pulse opposite polarity of minute pulse) or a separate wire for hour pulse. Later systems introduced serial digital communications but were never as widely installed as the minute and hour pulse systems in schools.
• jedberg 4y ago
  They had digital communication just not cheap ICs. I don't know how it worked but I imagine it was something like a mechanical switch that held the minute hand until it got a signal from the main office to start moving again. The clocks could even be set for Daylight time centrally, so I assume it had a way to send a signal that triggered a motor to move the hour hand faster.
  • tdeck 4y ago
    Since it's a school I wonder if they could just hold them back 1 or 11 hours on the weekend for DST changes. This would eliminate the need for an additional signal and circuitry on each follower clock.
• technothrasher 4y ago
  In the Standard Electric Time Company slave clocks that I've got, the master sends about a 12ms pulse once a minute, which pulls in a solenoid and allows a lever to ratchet one tooth on the minute wheel and advance the movement. Then once every twelve hours, the master sends a longer pulse, which pulls in a stronger second solenoid that allows the wheel to turn freely. There's a weight on the hour wheel which will pull the wheel around until the weight is on the bottom because of gravity, which corresponds with 12 o'clock. So no matter where the clock is, it will fall back to twelve with the longer pulse, and then begin the ratcheting again with the once a minute shorter pulses. (Sorry for the deprecated master/slave terminology, it's unfortunately what they used at the time)
  • Slava_Propanei 4y ago
    [dead]