Communications: electrical – Selective – Having indication or alarm
Patent
1973-01-02
1976-05-11
Caldwell, John W.
Communications: electrical
Selective
Having indication or alarm
307 10AT, 180114, B60R 2510
Patent
active
039567320
ABSTRACT:
A vehicle warning system is automatically armed via the ignition switch each time the ignition is turned off and the key removed so that no positive action of the driver is required. The system may be disabled between authorized uses of the vehicle through the ignition switch by turning to the accessory position. However, the arming circuit is so designed that the procedure may be reversed merely by reversing a lead connection at the time of installation.
The system is equipped with two sensing circuits one of which is adapted to sense the energization of a resistive load device and the other of which directly senses the opening of the hood and/or the tampering with selected areas of the vehicle protected by a closed loop circuit. A novel latching circuit is designed to selectively provide holding current for a latching SCR operatively connecting both sensing circuits to the alarm energizing circuitry and includes a field effect transistor controlled by the voltage level at its gate terminal provided through an RC network. That network provides a relatively long exit delay upon turning off the ignition during which the circuit will not latch in addition to an automatic alarm shutoff feature designed to unlatch the circuit after it has sounded for approximately five minutes. Manual switch means operatively connected to the aforementioned latching circuit is provided for permanently preventing the circuit from latching thereby to disable the circuit on a continuous basis without compromising the security of the circuit.
The alarm energizing circuitry is provided with an inherent entrance delay with means to bypass that delay when the cause of the alarm is other than the opening of a door of the vehicle. In addition, means are provided for bypassing the entrance delay and latching circuit completely regardless of the condition of the vehicle door in response to the actuation of the hood and tamper sensing circuit.
Finally, means are provided for maintaining the rate-of-change of battery voltage sensor insensitive to the turnoff of the vehicle headlights to account for delayed automatic headlight turn-off as is found in some late model vehicles.
REFERENCES:
patent: 3774191 (1973-11-01), Enemark
Caldwell John W.
Nowicki Joseph E.
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