Did You Know...
...that power steering was invented by independent inventor Francis W. Davis? As chief engineer in the 1920s of the truck division of the Pierce Arrow Motor Car Company, he saw how hard it was to steer heavy vehicles. So that he would be able to keep the profits from his future invention, Davis left his job, rented a small engineering shop in Waltham, Mass., and developed a hydraulic power steering system that led to power steering.
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| Number | Title | Issue Date |
| 5781622 | Two-line apparatus for telephone intercom An apparatus for providing an intercom function on a telephone, without the need for an external power supply, having DTMF or pulse capabilities including an intercom operation device arranged for connection to a DTMF or pulse telephone line and to a DTMF... | 07/14/1998 |
| 5459730 | Digital added main line system A method and apparatus for transmitting and receiving multiple telephone transmission signals over a single twisted pair. An analog signal from a local switching station is converted to an 80 kbits/sec signal for transmission over a twisted pair. A remote... | 10/17/1995 |
| 5428388 | Video doorbell system A communication apparatus for monitoring sounds and images at a remote location, such as the entranceway of a dwelling or other building includes a sensor station located at the entranceway, and a monitor station located within the building. A microphone ... | 06/27/1995 |
| 5148468 | Door answering system A door answering system is described for enabling the occupant of a structure (e.g., house, apartment, etc.) to provide a pre-recorded message to a visitor who has approached the entrance of the structure. The system includes a speaker/microphone and a ca... | 09/15/1992 |
| 5040207 | Two-telephone intercom A two-telephone intercom has a simple station-call signalling system. In the preferred embodiment, each telephone is provided with its own respective signalling unit comprising (a) a dc voltage source, (b) a voltage-sensitive threshold element (preferably... | 08/13/1991 |
| 4741031 | Intrinsically safe telephone An intrinsically safe telephone as provided for use in hazardous areas. The telephone includes a single line instrument located in the hazardous area which, in turn, is coupled by a two-wire transmission path to a shunt diode barrier and a telephone line ... | 04/26/1988 |
| 4716584 | Noise-free terminal station compatible with existing master stations A terminal station operating with a current supplied from a master station exchanges signals with it through cable conductors, one of the cable conductors being grounded at the master station to allow the current to return from the terminal station. A rec... | 12/29/1987 |
| 4584436 | Door-mounted combination intercom and viewer An improved door-mounted combination intercom and viewer is provided including a pair of identical housings, each having a microphone and a speaker therein. The microphones are isolated from contact with the housings by a vibration damping material to pre... | 04/22/1986 |
| 4022976 | Mechanically-coupled microphone-speaker unit and intercom system This invention describes an electromechanical sound apparatus which can be utilized as part of a sound system such as an intercom or as an acoustic repeater. The apparatus includes a loudspeaker having a diaphragm and a coil. The coil receives variations ... | 05/10/1977 |
| 3999015 | Aircraft multi-communications system An aircraft communication system adapted to provide a plurality of communication paths from respective inputs to a plurality of outputs, the communication paths being flexible in arrangement and operator control. For use in an aircraft, the system combine... | 12/21/1976 |
| 3997733 | Intrinsically safe communication systems The invention is a communications and tone control system for use between safe and hazardous areas. The invention's field terminals operate in hazardous areas and are limited to low, intrinsically safe power levels by the use of zener barriers and current... | 12/14/1976 |
| 3952155 | Water ski tow communication system A water ski tow assembly is provided which incorporates a two-way communication system between the skier and the operator of a towing boat. The communication system includes a first microphone/speaker unit mounted in the towing boat and electrically coupl... | 04/20/1976 |
