Signaling circuit and method to detect zone status

1. A current loop circuit comprising:

an AC signal generator to generate an AC signal having a positive half cycle and a negative half cycle;

a bi-directional current limiter configured to receive the AC signal and bi-directionally limit the loop current to a predetermined current value (I 3 );

a first zone configured to receive the AC signal, the first zone including a unidirectional current limiter to limit a unidirectional current (I 1 ) that is proportionately less than the bi-directionally limited current I 3 ;

a second zone configured to receive the AC signal, the second zone including a unidirectional current limiter to limit a unidirectional current (I 2 ) that is proportionally less than the bi-directionally limited current I 3 ;

a first opto-coupler circuit (ISO 1 ) configured to detect both high and low current states in the current loop circuit;

a second opto-coupler circuit (ISO 2 ) associated with the first zone and configured to detect only high current states in the current loop circuit; and

a third opto-coupler circuit (ISO 3 ) associated with the second zone and configured to detect only high current states in the current loop circuit.

2. The current loop circuit of claim 1 , the first zone active on the positive half cycle of the generated AC signal wave and further comprising a switch (K 1 ) to detect a zone status such that when the switch (K 1 ) is open the loop current is I 1 and ISO 2 yields a status of OFF; and when the switch (K 1 ) is closed the loop current is I 3 and ISO 2 yields a status of ON.

3. The current loop circuit of claim 1 , the second zone active on the negative half cycle of the generated AC signal and further comprising a switch (K 2 ) to detect a zone status such that when the switch (K 2 ) is open the loop current is I 2 and ISO 3 yields a status of OFF; and when the switch (K 2 ) is closed the loop current is I 3 and ISO 3 yields a status of ON.

4. The current loop circuit of claim 1 , ISO 2 and ISO 3 each including an LED that emits light when a status is ON during a corresponding half cycle of the generated AC signal, the ON status known after a complete AC cycle.

5. The current loop circuit of claim 1 , ISO 1 to yield a status of OFF when there is an open loop condition in the current loop.

6. The current loop circuit of claim 1 , the AC signal generator to generate the AC signal using a push-pull technique and two (2) pulse width modulation (PWM) outputs of a microcontroller in which the isolated output is the secondary coil of an isolation transformer.

7. The current loop circuit of claim 1 , wherein:

I 1 is equal to I 2 ; and

I 1 /I 3 and I 2 /I 3 is approximately 0.1.

8. A method of zone signaling in an alarm system using a current loop circuit, the method comprising:

generating an AC signal wave having a positive half cycle and a negative half cycle;

limiting a loop current resulting from the generated AC signal to a value (I 3 ) using a bi-directional current limiter;

further limiting the loop current resulting from the generated AC signal to a value (I 1 ) using a unidirectional current limiter in a first zone or a value (I 2 ) using a unidirectional current limiter in a second zone, I 1 and I 2 being proportionally less than I 3 ;

monitoring a first opto-coupler circuit (ISO 1 ), ISO 1 to detect high or low current states for the loop current;

monitoring a second opto-coupler circuit (ISO 2 ) associated with the first zone, ISO 2 to detect only high current states during the positive half cycle of the AC signal wave; and

monitoring a third opto-coupler circuit (ISO 3 ) associated with the second zone, ISO 3 to detect only high current states during the negative half cycle of the AC signal wave.

9. The method of claim 8 , further comprising:

determining the state of a switch (K 1 ) in the first zone such that when the switch (K 1 ) is open the loop current is I 1 and ISO 2 yields a status of OFF; and when the switch (K 1 ) is closed the loop current is I 3 and ISO 2 yields a status of ON during a corresponding half cycle of the generated AC signal, the ON status known after a complete AC cycle.

10. The method of claim 8 , further comprising:

determining the state of a switch (K 2 ) in the second zone such that when the switch (K 2 ) is open the loop current is I 2 and ISO 3 yields a status of OFF; and when the switch (K 2 ) is closed the loop current is I 3 and ISO 3 yields a status of ON.

11. The method of claim 8 , ISO 2 and ISO 3 each including an LED that emits light when a status is ON during a corresponding half cycle of the generated AC signal, the ON status known after a complete AC cycle.

12. The method of claim 8 , ISO 1 to yield a status of OFF when there is an open loop condition in the current loop.

13. The method of claim 8 , wherein:

I 1 is equal to I 2 ; and

I 1 /I 3 and I 2 /I 3 is approximately 0.1.

14. A zone status detection circuit comprising:

an AC signal generator to generate an AC signal having a positive half cycle and a negative half cycle coupled in series with:

a first resistor having a value R 2 that ensures a comfortable current for a first opto-coupler circuit (ISO 1 ), the first opto-coupler circuit (ISO 1 ) configured to detect current in the zone status detection circuit;

a first zone including a resistor of value R 1 coupled in parallel with a first diode conductive during the positive half cycle and a first switch (K 1 ), the first zone associated with a second opto-coupler circuit (ISO 2 ) configured to detect a voltage on the resistor in the first zone;

a second zone including a resistor of value R 1 coupled in parallel with a second diode conductive during the negative half cycle and a second switch (K 2 ), the second zone associated with a third opto-coupler circuit (ISO 3 ) configured to detect a voltage on the resistor in the second zone; and

a load resistor (R LOAD ) set to a value to ensure there is no output on ISO 2 and ISO 3 when switches K 1 and K 2 are both open but have a pulsed output on ISO 2 or ISO 3 when either switch K 1 or K 2 is closed.