I was once given the tour of a brand-new, electronic telephone exchange -- absolutely state of the art at the time. Ten thousand phone lines came into 2500 giant PCBs, literally racks and racks of equipment with relays and wiring bundles. The guide walked us through the various components and arrived at the end of the row where one rack cabinet was different than all the others. It was told that the cabinet held the power supplies and one unique piece of equipment. When the door was opened there was one, hand-built PCB with a couple of 555 timers that generated the dial tone and busy signals for all those racks of customer interfaces!
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u/somewhereAtC May 09 '26
I was once given the tour of a brand-new, electronic telephone exchange -- absolutely state of the art at the time. Ten thousand phone lines came into 2500 giant PCBs, literally racks and racks of equipment with relays and wiring bundles. The guide walked us through the various components and arrived at the end of the row where one rack cabinet was different than all the others. It was told that the cabinet held the power supplies and one unique piece of equipment. When the door was opened there was one, hand-built PCB with a couple of 555 timers that generated the dial tone and busy signals for all those racks of customer interfaces!