Level detection circuit

Claim 2

A level detection circuit comprising: converter means (R1) for converting a physical quantity into an electric quantity; an amplifier (A) connected to the output terminal of said converter means, said amplifier having a threshold level; first and second switching elements (T2,T1) connected to the output side of said amplifier to be driven alternately thereby; first and second display lamps (L1, L2) controlled by the outputs of said first and second switching elements, respectively; a feedback capacitor (C) connected between the output of said first switching element (T2) and the input of said amplifier (A); and a feedback resistor (Rf) connected between the output of said second switching element (T1) and the input of said amplifier (A); wherein, when the output of said converter means exceeds the threshold level of said amplifier, said amplifier is operated to energize either said first or second switching element, the output of said first or second switching element being fed back to the input of said amplifier through said capacitor (C) and resistor (R), respectively, so as to selectively illuminate said first and second display lamps.

Claim 3

The circuit according to claim 1 wherein said first and second switching elements comprise transistors (T1, T2) connected in cascade, and said first and second display lamps are respectively connected to the collector electrodes of said transistors.

Claim 4

Circuit according to claim 1, wherein the threshold level of the amplifier (A), the electric quantity, the capacitance of the capacitor (C) and the resistance of the resistor (Rf) are so relatively adjusted that, when the output of the converter means (R1) just exceeds the threshold level of the amplifier, the amplifier is operated to energize the switchiNg element (T1, T2) alternately, the output of said switching elements being fed back to the input of the amplifier over said capacitor (C) and resistor (R) so that oscillations will result to selectively, alternately illuminate the first and second display lamps; and, when the output of the converter means (R1) is beyond the threshold level, holding the amplifier in stable de-energized or energized operation, one of said switching elements only is continuously energized to selectively, continuously energize the one or other of said display lamps (L1, L2).

Claim 5

Circuit according to claim 3, wherein the feedback capacitor (C) and the feedback resistor (Rf) form a feedback circuit for the amplifier (A), said circuit comprising impedance coupling means (R3) connecting the output of said converter means (R1) to the input of the amplifier, the respective relative values of the coupling means and the impedance of the feedback circuit determining the range of unstable operation of the amplifier.

Claim 6

Light level indicator circuit comprising converter means (R1) for converting light levels into an electrical signal; an amplifier (A) connected to the output terminal of the converter means (R1), said amplifier having a threshold level (Vp); first (T2) and second (T1) switching elements connected to the output side of said amplifier (A) to be driven alternately thereby; first (L1) and second (L2) display lamps controlled by the outputs of said first and second switching elements, respectively; a capacitor (C) connected between the output of said first switching element (T2) and the input of the amplifier and a resistor (Rf) connected between the output of the second switching element (T1) and the input of the amplifier (A); wherein the threshold levels of the amplifier (A), the electrical signal, the capacitance of the capacitor (C) and the resistance of the resistor (Rf) are so relatively adjusted and dimensioned that, when the output of the converter means (R1) just exceeds the threshold level of the amplifier, the amplifier is operated unstably to energize either said first or second switching element (T1, T2), the output of either said first or second switching element being fed back to the input of said amplifier over said capacitor (C) and resistor (Rf) so that oscillations will result, and to selectively alternately illuminate the first and second display lamp; and, when the output of said converter means (R1) is beyond the threshold level of the amplifier (A) and holding the amplifier in stable de-energized or energized condition, a respective one of said switching elements only is continuously energized to selectively continuously energize one or the other of said display lamps (L1, L2).

Claim 7

Light level indicator circuit comprising converter means (R1) for converting light levels into an electrical signal; an amplifier (A) connected to the output terminal of the converter means (R1), said amplifier having a threshold level (Vp); first (T2) and second (T1) switching elements connected to the output side of said amplifier (A) to be driven alternately thereby; first (L1) and second (L2) display lamps controlled by the outputs of said first and second switching elements, respectively; a capacitor (C) connected between the output of said first switching element (T2) and the input of the amplifier and a resistor (Rf) connected between the output of the second switching element (T1) and the input of the amplifier (A); wherein the threshold levels of the amplifier (A), the electrical signal, the capacitance of the capacitor (C) and the resistance of the resistor (Rf) are so relatively adjusted and dimensioned that, when the output of the converter means (R1) just exceeds the threshold level of the amplifier, the amplifier is operated unstably to energize either said first or second switching element (T1, T2), the output of either said first or second switching element being fed back to the input of said amplifier over said capacitor (C) and resistor (Rf) so that oscillations will result, and to selectively alternately illuminate the first and second display lamp; and, when the output of said converter means (R1) is beyond the threshold level of the amplifier (A) and holding the amplifier in stable de-energized or energized condition, a respective one of said switching elements only is continuously energized to selectively continuously energize one or the other of said display lamps (L1, L2).

Claim 8

Circuit according to claim 5, wherein said first and second switching elements comprise transistors connected in cascade, and said first and second display lamps are respectively connected to the collector electrodes of said transistors.

Claim 9

Circuit according to claim 5, wherein the feedback capacitor (C) and the feedback resistor (Rf) form a feedback circuit for the amplifier (A), and said circuit further comprises a coupling resistor (R3) connecting the output of said converter means (R1) to the input of the amplifier, the respective relative resistance values of the coupling resistor (R3) connected to the input of the amplifier, and of the resistance of the feedback circuit being set to determine the range of unstable operation of the amplifier.

Claim 10

Circuit according to claim 5, for use in a camera to indicate proper exposure, further comprising a source of power (E) to energize the amplifier, the switching elements, and the display lamps; wherein the amplification of the amplifier, the potential supplied by the power source (E), the resistance value of the coupling resistor (R3), the feedback resistor (Rf) and the resiStance of the converter means (R1) are relatively selected to provide: a. constant illumination of the first display lamp (L1) representative of excess light being detected; b. constant illumination of the second display lamp (L2) being representative of deficient light being detected; and c. alternate flashing of both said lamps being indicative of proper light level.