When using a closed circuit telephone system, the voltage is often too low to drive the ringer in any phone. In this case, we can substitute Buzzers, which are electromechanical noise makers running on direct current.
New Buzzer System
The Buzzer system envisioned to accompany the new telephone system had a buzz box in each room of the Habitat that contained a telephone. Each buzz box contained:
- 9V Buzzer (25mA)
- 2V Green LED (10mA)
- 2V Yellow LED (10mA)
- single throw, single pole, momentary switch
Signals ran to and from each buzz box along the Green and Brown CAT5 components in the cables that were already running the Telephone system along their Purple and Orange components.
In the simulator loft a card sends resistor modulated voltage to the buzz box along the green solid and brown solid. Voltage returns along the green and brown stripe wires. The brown stripe wires are all connected to Pin 10 of a parallel port, and the green stripes are individually connected to the collector of an NPN transistor. The base of each transistor is powered by Pins 2 thru 6 of the parallel port.
This setup allows the Habitat to Buzz Mission Control by throwing the switch in the buzz box, and Mission Control to buzz a single room in the Habitat by entering a command on the keyboard corresponding to the Pin 2 thru 6 on the parallel port (this is handled in software).