Circuit and method for controlling an alarm

• US 6,346,880 B1
• Filed: 12/20/1999
• Issued: 02/12/2002
• Est. Priority Date: 12/20/1999
• Status: Expired due to Term

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Wicka, Stanislaw K., Schroeder, Stanley J., Gomez-Torres, Leticia, Gutierrez, Juan M.
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US09/468,417
• Time in Patent Office: 785 Days
• Field of Search: 340/506, 340/510, 340/511, 340/526, 340/628, 340/629, 340/330, 340/661
• US Class Current: 340/506
• CPC Class Codes: G08B 13/22 Electrical actuation
• CPC Class Codes: G08B 17/00 Fire alarms; Alarms responsive to explosion
• CPC Class Codes: G08B 29/145 of fire detection circuits

Abstract

An alarm circuit (10) includes a sensor (11), a comparator (13), a control circuit (16), and a transducer (19). The control circuit (16) controls the transducer (19) and has three modes of operation: standby mode, alarm mode, and silence mode. The comparator (13) compares the voltage of an input signal from the sensor (11) to a first threshold level during the standby mode of operation. The control circuit (16) enables the transducer (19) and transitions to the alarm mode of operation after the voltage of the input signal exceeds the first threshold level. The control circuit (16) disables the transducer (19) for a predetermined time period and transitions to the silence mode of operation after a silence signal is received by the control circuit (16). The input signal is compared to both the first threshold level and a second threshold level during the silence mode. The silence mode can be terminated if the voltage of the input signal falls below the first threshold level or if the voltage of the input signal rises above the second threshold level. In addition, the silence mode can be terminated if the control circuit (16) receives a reset signal or a remote signal from a remote unit.

Claims

1. A circuit for controlling an alarm, comprising:

a comparator having a first input coupled for receiving an input signal, a second input, and an output;

a multiplexer having a first input coupled for receiving a first reference signal, a second input coupled for receiving a second reference signal, a third input coupled for receiving a select signal, and an output coupled to the second input of the comparator; and

a control circuit having an input coupled to the output of the comparator, a first output for providing the select signal, and a second output for providing a control signal for controlling the alarm.

2. The circuit of claim 1, further including a sensor coupled to the first input of the comparator for providing the input signal.

3. The circuit of claim 2, wherein the sensor is an ion sensor.

4. The circuit of claim 2, wherein the sensor is a photoelectric sensor.

5. The circuit of claim 1, further including an oscillator coupled to a second input of the control circuit.

6. The circuit of claim 1, wherein the control circuit includes a latch having an input coupled to the output of the comparator and an output coupled to the second output of the control circuit and the third input of the multiplexer.

7. The circuit of claim 6, wherein the control circuit further includes a counter having an output coupled to the input of the latch.

8. The circuit of claim 7, wherein the latch is a flip-flop having a reset input coupled to the output of the comparator, a data input coupled for receiving a power supply voltage, a clock input coupled to a second input of the control circuit, and an output coupled to the second output of the control circuit.

9. The alarm circuit of claim 8, wherein the control circuit further includes:

a first AND gate having a first input coupled to the output of the comparator and an output;

a second AND gate having a first input coupled to the output of the comparator and an output;

a third AND gate having a first input coupled to the output of the comparator and an output coupled to the second output of the control circuit; and

an OR gate having a first input coupled to the output of the first AND gate, a second input coupled to the output of the second AND gate, a third input coupled to the output of the counter, and an output coupled to the reset input of the flip-flop.

10. The circuit of claim 9, wherein the control circuit further includes a fourth AND gate coupled between the output of the latch and the third input of the multiplexer, wherein the fourth AND gate has a first input terminal coupled for receiving a clock signal, a second input terminal coupled to the output of the output of the flip-flop, and an output commonly coupled to the third input of the multiplexer, a second input of the first AND gate, a second input of the second AND gate, and a second input of the third AND gate.

11. The circuit of claim 1, wherein the control circuit is a microprocessor that enables the alarm when a magnitude of the input signal is greater than a magnitude of the first reference signal, disables the alarm when the magnitude of the input signal is less than the magnitude of the first reference signal, and enables the alarm when a magnitude of the input signal is greater than a magnitude of the second reference signal.

12. A method for controlling an alarm, comprising the steps of:

operating in an alarm mode of operation after an input signal exceeds a first threshold level, wherein the alarm is enabled during the alarm mode;

operating in a silence mode of operation after a silence signal is received, wherein the alarm is disabled during the alarm mode; and

comparing the input signal to the first threshold level during the silence mode of operation.

13. The method of claim 12, further including the step of comparing the input signal to a second threshold level during the silence mode.

14. The method of claim 13, further including the step of transitioning from the silence mode to the alarm mode after the input signal exceeds the second threshold level.

15. The method of claim 12, further including the step of transitioning from the silence mode to a standby mode of operation after the input signal decreases below the first threshold level, wherein the alarm is disabled during the standby mode.

16. The method of claim 12, wherein the step of operating in the silence mode includes disabling the alarm for a predetermined time period during the silence mode.

17. The method of claim 16, further including the step of terminating the silence mode before the predetermined time period ends.

18. The method of claim 12, further including the step of terminating the silence mode after receiving a reset signal.

19. The method of claim 12, further including the step of terminating the silence mode after receiving a remote signal from another alarm.

20. A method for controlling an alarm, comprising the steps of:

enabling the alarm after a magnitude of an input signal increases to a level above a first threshold level;

disabling the alarm after receiving a silence signal; and

comparing the magnitude of the input signal to the first threshold level after receiving the silence signal.

21. The method of claim 20, further including the step of comparing the magnitude of the input signal to a second threshold level after receiving the silence signal.