Alarm circuit
First Claim
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1. An alarm circuit comprising a first terminal means adapted for connection to a supply potential source, an alarm means capable of being energized by said supply potential and connected between said first terminal means and a reference ground potential point through first and second series-connected switching means;
- third and fourth series-connected switching means connected between said first terminal means and a reference ground potential point;
each of said first, second, third and fourth switching means having a control electrode for selectively enabling or disabling said switching means in accordance with the potential at the respective control electrode;
said control electrode of said first switching means further being connected through a series-connected first unidirectional current passing means and a sensing circuit to second terminal means and, the control electrode of said first switching means being connected through second unidirectional current passing means to third terminal means, whereby said first switching means closes in response to potential from said third terminal means and said sensing circuit, said first and second unidirectional current passing means isolating said second and third terminal means from one another whilst providing current paths therethrough from said second and third terminal means respectively to said control electrode of said first switching means; and
the control electrodes of said second, third and fourth switching means being connected to said first, third and second terminal means, respectively, whereby said third and fourth switching means close in response to potential from both of said second and third terminal means and thereby cause said second switching means to open, and said second switching means is closed when at least one of said third and fourth switching means is open.
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Abstract
An alarm circuit for vehicle headlights including a switching circuit which provides a warning when the headlights should be activated in accordance with ambient conditions, such as low light levels, as well as warning of when the headlights should be de-activated, as when the vehicle ignition system is switched off.
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Citations
5 Claims
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1. An alarm circuit comprising a first terminal means adapted for connection to a supply potential source, an alarm means capable of being energized by said supply potential and connected between said first terminal means and a reference ground potential point through first and second series-connected switching means;
- third and fourth series-connected switching means connected between said first terminal means and a reference ground potential point;
each of said first, second, third and fourth switching means having a control electrode for selectively enabling or disabling said switching means in accordance with the potential at the respective control electrode;
said control electrode of said first switching means further being connected through a series-connected first unidirectional current passing means and a sensing circuit to second terminal means and, the control electrode of said first switching means being connected through second unidirectional current passing means to third terminal means, whereby said first switching means closes in response to potential from said third terminal means and said sensing circuit, said first and second unidirectional current passing means isolating said second and third terminal means from one another whilst providing current paths therethrough from said second and third terminal means respectively to said control electrode of said first switching means; and
the control electrodes of said second, third and fourth switching means being connected to said first, third and second terminal means, respectively, whereby said third and fourth switching means close in response to potential from both of said second and third terminal means and thereby cause said second switching means to open, and said second switching means is closed when at least one of said third and fourth switching means is open. - View Dependent Claims (2, 3, 4, 5)
- third and fourth series-connected switching means connected between said first terminal means and a reference ground potential point;
Specification