JPS5952374B2 - Exposure warning circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exposure warning circuit for use in a camera, etc., to warn a photographer of appropriate or inappropriate exposure, camera shake, etc. using a photovoltaic element such as a phototransistor. The present invention relates to an exposure warning circuit that is easy to set and whose appropriate range is not affected by the degree of amplification.

A conventional general exposure warning circuit is shown and explained in FIG. 1. In the figure, A is an amplifier, and the first and second input terminals V
.

Na, VlNb and the first and second output terminals VOa, O
b, the first input VlNa and the second input VINb are compared, and if VINb>,Na, the first output 0a is turned off, the second output VOb is turned on, and VlNb<1Na
If so, the configuration is such that the first output VOa is turned on and the second output VOb is turned off. PD is a photovoltaic element and is inserted between the base and collector of the transistor Tr. VR is a reference voltage source, and one end is connected to the first input terminal VlNa of the amplifier A, and the other end is grounded via a diode D1. LO and Lu are exposure warning elements (hereinafter referred to as indicator lights) that indicate overexposure or underexposure; one end is connected to the power supply VB via a switch SW, and the other end is the second output terminal of amplifier A. Connected to VOb and VOa, respectively. RO and Ru are resistors for detecting a current of 10, one end of which is connected to the emitter of the transistor Tr via a switch SW, and the second input terminal V of the amplifier A.
1Nb, and the other end is grounded via a diode D1. In a circuit with such a configuration, amplifier A
A reference voltage Vr is supplied from a reference voltage source VR to the first input terminal VlNa of the photovoltaic element P, and a photovoltaic element P is supplied to the second input terminal V, Nb.
The photocurrent of D or the current 10 proportional to the photocurrent is connected to the resistor R.
u or resistor RO, and interlock the switch SW as shown in the figure.When the movable contact of the switch SW is on the terminal a side, IORu<r, that is, VlNb.
<VlNa, the first output 0a of amplifier A is on,
No. The output 0b of No. 2 is turned off and the camera shake warning indicator light Lu is turned on. Here, if IORu>Vr, the first output 0a is turned off and the indicator light Lu does not light up. Also, when the movable contact of the switch SW is closed to terminal b, IORO>
Vr, i.e. V. If Nb>VlNa, the first output VOa of the amplifier A is turned off, the second output 0b is turned on, and the overexposure warning LO is turned on. Here ゛IORO
<If Vr, the first output 0a is on, the second output VOb
is turned off and the indicator light LO does not light up. By switching the switch SW in this way, first IORu<Vr.
In this case, the indicator light Lu lights up to warn the photographer of camera shake. Next, when IORO<Vr<IORu, neither of the indicator lights LO and Lu turns on, indicating that the exposure is appropriate. If Vr<IORO, the indicator light LO lights up to notify the photographer of overexposure. However, such an exposure warning circuit has the disadvantage that no information is displayed when the exposure is appropriate, which makes the photographer feel uneasy, which is not desirable in practice.

In addition, it is inconvenient because it requires manual switching operation, and it is necessary to use an interlocking switch.In other words, it is necessary to construct the lamp circuit after constructing the check circuit represented by the resistors Ru and RO. If the order is reversed, the checker will be activated even momentarily before the check circuit is formed, which may cause erroneous lighting, resulting in a disadvantage that it becomes mechanically complex and uneconomical. , In view of the above points, the present invention has been made to solve such problems and eliminate such drawbacks.The purpose of the present invention is to provide a stable circuit with an appropriate range determined by a simple circuit configuration, and
The appropriate range is not affected by the degree of amplification, and furthermore, the appropriate/inappropriate exposure and camera shake warnings are electronically displayed without using a mechanical switch, and even when the exposure is appropriate. It is an object of the present invention to provide an exposure warning circuit that can display the exposure warning circuit and eliminate the need to rely on artificial switching operations as in the past, thereby solving all the inconveniences caused by this.

In order to achieve such an object, the present invention has a first input terminal to which a comparison voltage is applied, a second input terminal to which a detection voltage is applied, a first output terminal, and a second output terminal. When the input potential of the first input terminal is higher than the input potential of the second input terminal, the first output terminal becomes conductive and the second output terminal becomes non-conductive, and the input potential of the first input terminal is lower than the input potential of the second input terminal. an amplifier whose second output terminal becomes conductive and whose first output terminal becomes non-conductive; a comparison voltage source that supplies the comparison voltage to the first input terminal of the amplifier; and the second input terminal and the second output terminal. a first resistor connected between the first resistor and the second input terminal, which is connected to the first resistor and cooperates with the first resistor depending on the output state of the amplifier to supply a voltage corresponding to the brightness of the subject to the second input terminal. a first input terminal to which the comparison voltage is applied; a detection resistor; a first display element connected to the first output terminal; and a second display element connected to the second output terminal; Potential and the first resistance and detection. The detected voltage of the second input terminal determined by the resistance is compared with the detected voltage of the second input terminal by the amplifier.
The first display element of the amplifier is turned on at an appropriate value. and ``The detected voltage at the 21st input terminal, which changes depending on the output state of the second output terminal, causes the amplifier to oscillate at the propagation delay period of the amplifier, causing the first and second display elements to alternately blink. and a first resistor connected between the second input terminal and the second input terminal at least during photometry, and a first resistor connected to the first resistor and whose output voltage varies depending on the output state of the amplifier. A detection resistor that cooperates with one resistor to supply a voltage according to the brightness of the subject to the second input terminal, a charging capacitor connected in series with this detection resistor, and the four capacitors mentioned above are short-circuited during photometry. a switch that opens the short-circuit of the capacitor and short-circuits the detection resistor in synchronization with the opening of the shutter; a first display element connected to the first output terminal; and a second display element connected to the second output terminal. a display element, and the voltage at the first input terminal to which the comparison voltage is applied and the detection voltage at the second input terminal determined by the resistance ratio of the first resistor and the detection resistor are detected by the amplifier. By comparison, when the value is not appropriate, either the first display element or the second display element is turned on, and when the value is appropriate, the second display element is turned on, which changes depending on the output states of the first and second output terminals.
The detected voltage at the input terminal causes the amplifier to oscillate at a propagation delay period of the amplifier, thereby causing the first and second display elements to alternately blink.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the exposure warning circuit according to the present invention.

In the figure, A is the first and second input terminals V1, 8, V1
Nb, and a comparator amplifier having first and second output terminals VOa and VOb, and has a function of inverting and opposing outputs depending on input conditions. That is, the first input V,,8 and the second input,..., are ~71, 10>V1. Then, the second output VOb is turned on and the first output VOa is turned off, and if VlNb<VlN, the second output 0b is turned on.
is turned off, and the first output VOa is turned on. The PD is a photovoltaic element that measures the brightness of an object and is inserted between the collector and base of the transistor Tr. Here, the collector of the transistor Tr is connected to the power supply VB, and the emitter is grounded through a resistor Ru and a diode D1 in series. Here, IO indicates a current proportional to the photocurrent of the photovoltaic element PD. VR is amplifier A
This is a reference voltage source for applying a reference voltage Vr to the first input VlNa of , one end of which is connected to the first input terminal VON8, and the other end of which is grounded via a diode D1. The second input terminal VIN6 of the amplifier A is connected to the connection point between the emitter of the transistor Tr and the resistor Ru, and is also connected to the second output terminal VOb of the amplifier A via the resistor RO and the diode D2 in series. ing. Here, the resistors RO and Ru are resistors for detecting the current 10, that is, detecting the subject brightness. Further, the first output terminal VOa is connected to the power supply VB via the camera shake warning indicator Lu, and the second output terminal 0b is connected to the power supply VB via the overexposure warning indicator LO.
Connected to B. Next, the operation of the embodiment shown in FIG. 2 will be explained.

Now, regarding the input conditions of the reference voltage Vr from the reference voltage source VR and the voltage to be determined that changes depending on the physical quantity, 1
r<IO(RO'Ru), 2I0(RO'Ru)<r<
Considering the three conditions IORu, 3I0Ru〈r,
First, when Vr<IO(RO'Ru) of 1, the detection resistor RO and Ru are parallel resistors, and the second output VOb is on. Here, the second output V
Ob turns on under the input condition of VINa<VINb, and IO(RO'Ru)>r holds true. In other words, the current O proportional to the photocurrent of the photovoltaic element PD is large, and when condition 1 is met, the second output VOb is maintained in the on state, thereby lighting up the indicator lamp LO and preventing overexposure. Alert the photographer. Next, 2 (RO'Ru)
When Vr<IORu, the first output VOa is now off,
If the second output VOb is on, the second input VlNb is I
Since VlN6<VlNa, the first output VOa is turned on and the second output VOb is turned off. When the first output 0a is turned on and the second output VOb is turned off, the second input V. Nb becomes IORu and V,
Since Nb>VlNa, the first output VOa is turned off.
The second output VOb is turned on. In this way IO(RO
'Ru) <When r<IORu, the first and second outputs VOa and VOb are alternately turned on and off, and the amplifier A
oscillates, and the indicator lights LO and Lu light up alternately. Here, the period of this lighting is determined by the propagation time of the amplifier from when the input is applied to amplifier A until the output is reversed, and is very fast, so it appears that both indicator lights LO and Lu are lit at the same time. looks like. This indicates that the exposure is appropriate. In addition, when IORu<Vr of 3, V
lN6<V, N8, the first output VOa is on,
The second output VOb is turned off and no current flows through the resistor RO, so the input conditions are maintained and the indicator light Lu lights up, indicating that the subject is dark, the current 10 is small, and the shutter time is long. to warn the photographer. In this way, in the present invention, a detection resistor R with a current of 10 is proportional to the photocurrent of the photovoltaic element PD that measures the brightness of the subject.
It is possible to automatically switch between O and Ru without using a mechanical interlocking switch, to display an exposure warning, and to indicate when the exposure is appropriate.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

In FIG. 3, the same reference numerals as in FIG. 2 indicate corresponding parts, and D3 is a diode connected in series with the resistor Ru. The connection point between the second input terminal V, Nb of the amplifier A and the emitter of the transistor Tr is connected to the second output terminal V of the amplifier A through the resistor RO and the diode D2 in the forward direction.
Ob and the indicator light LO, and also connected to the first output terminal VOa of the amplifier A and the indicator light Lu via a resistor Ru and a diode D3 in the forward direction. The exposure warning circuit configured in this manner performs the same operation as shown in FIG.
When , both the indicator lights LO and Lu light up alternately and the dew 9
The camera shake warning indicator light Lu lights up when IORu<Vr. FIG. 4 is a circuit diagram showing still another embodiment of the present invention, in which a current of 10
The detection resistor RO is connected in series with the resistor 4 resistor Ru, and the resistor RO
, Ru is connected to the second output terminal of the amplifier A and the indicator light LO through the diode D2 in the forward direction to issue an exposure warning. Note that the same parts as in FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. In the exposure warning circuit configured in this way, when Vr is 10R0, the indicator light LO lights up to warn the photographer of overexposure, and when IORO<Vr<IO (RO+Ru), both the indicator lights LO and Lu turn on. lights up alternately to indicate proper exposure, and when IO (RO+Ru) <Vr, the indicator light Lu
lights up to warn you of camera shake. FIG. 5 is a circuit diagram showing another embodiment of the present invention. In FIG. 5, the same reference numerals as in FIG. 4 indicate corresponding parts, and A1 is the amplifier in FIG. 1 and corresponds to amplifier A shown in FIG. 2. A2 is a second amplifier connected to the output of the amplifier A1 shown in FIG. It is connected to a power source VB, and the other end is connected to indicator lights Lu and LO. A common connection point of the indicator lights Lu and LO is connected to a power source VB via a resistor R. In the exposure warning circuit configured in this manner, the second amplifier A2 operates only when the first amplifier A1 oscillates, turns on the output, and lights up the indicator light La to indicate that the exposure is appropriate. . Note that at this time, the indicator lights LO and Lu are turned off. To elaborate on this,
When Vr<IORO, the indicator light LO lights up to warn the photographer of overexposure, and when IORO<Vr<IO(RO+R
When u), the indicator light La lights up to show that the exposure is appropriate, and when IO(RO+Ru)<Vr, the indicator light L lights up.
u lights up to warn the photographer of camera shake. In each of the above embodiments, the case where the indicator light Lu is used as an indicator light indicating the limit of camera shake has been described, but it can also be used in the shutter speed priority readout system as an indicator of underexposure. In this case, the time-fixing resistor (not shown) and the reference voltage source VR may be linked in a fixed relationship. Furthermore, in the above embodiment, a case was explained in which an indicator light was used as an exposure warning display element.
The present invention is not limited thereto, and a light emitting diode (LED) can also be used as the exposure warning display element.

FIG. 6 shows one embodiment thereof. That is, as shown in FIG. 6, the light emitting diodes LEDu, LEDO
One end is connected in common, and the connection point is connected to the power supply VB via the protective resistor R, and the light emitting diode EDu, LED
The other end of O is the first and second output end VOa of amplifier A,
Each is connected to Ob.

The operation of appropriate/inappropriate exposure and camera shake warning in this circuit is exactly the same as that shown in FIG. 2 using the above-mentioned indicator light, so a description thereof will be omitted here. Furthermore, the third
In the embodiments shown in FIGS., 4 and 5 as well, the light emitting diode LED can be replaced with the indicator light emitting diode by connecting a protective resistor in series with the light emitting diode LED as shown in FIG. Further, the present invention is not limited to only a photovoltaic element as an element for measuring the brightness of a subject, and a photodiode can also be replaced with a photoconductive element Cds.

An example is shown in FIG. FIG. 7 shows an example in which the photovoltaic device PD in FIG. 4 is replaced with a photoconductive device Cds. That is, the photovoltaic current amplification circuit composed of a photovoltaic element PD and a transistor Tr is replaced with a photoconductive element Rcds, and the reference voltage source VR is composed of a voltage dividing resistor R1 and a resistor R2. It has the same configuration as FIG. 4. In this circuit, the indicator light LO lights up at , the indicator light Lu lights up at , and both the indicator lights LO and Lu light up alternately at .

Note that in this embodiment, the reference voltage source VR is configured by the resistor R1 and the resistor R2 that form a voltage dividing circuit, but the present invention is not limited to this, and other bias power sources may be used. Needless to say. Also in FIGS. 2, 3, and 5, the photovoltaic current amplification circuit composed of the photovoltaic device PD and the transistor Tr can be replaced with a photoconductive device Cds. In this case as well, the indicator light L
It is clear from the above explanation that by setting the reference voltage Vr to an intermediate value between the lighting conditions of O and the lighting conditions of the indicator light Lu, a condition is obtained in which both the indicator lights LO and Lu are lit alternately. be. FIG. 8 is a circuit configuration diagram when an embodiment of the exposure warning circuit according to the present invention is applied to an electric shutter circuit, and shows an example of application to an electric shutter circuit equipped with the display function shown in FIG. be.

In FIG. 8, the same reference numerals as those in FIG. SW is a trigger switch that switches from terminal a to terminal B at the same time as the shutter opens, α is a charging capacitor that determines the shutter time, and a detection resistor RO with a current of 10 is proportional to the photocurrent of the photovoltaic element PD. , Ru are connected in series. The trigger switch SW is configured to short-circuit the capacitor Cc at the time of exposure warning 2, open the short-circuit of the capacitor Cc in synchronization with the shutter opening, and short-circuit the detection resistors RO and Ru. That is, first, when the trigger switch SW is at terminal a, the capacitor Cc is short-circuited to issue an exposure warning. Next, in synchronization with the shutter opening, the trigger switch SW switches from terminal a to terminal b, and the detection resistor R
Short-circuit O and Ru. At this time, since VlNa>1N5, the first output VOa is turned on, and current flows through the magnet MG to maintain the shutter level. Then, the charging capacitor Cc is gradually charged by the current 10,
When the charging voltage of the capacitor Cc reaches the reference voltage r, the first
The output VOa is turned off, the power to the magnet MG is cut off, and the shutter is closed. Note that FIGS. 2, 3, and 7 can also be constructed in the same manner. Further, in the present invention, it is possible to limit the incident light to the photovoltaic element PD, etc. by aperture, insert an ASA, etc., or by changing the reference voltage Vr, aperture and insert an ASA. .

As is clear from the above description, according to the present invention, the potential of the first human power terminal to which the comparison voltage is applied is changed depending on the output state of the amplifier, and appropriate exposure can be displayed without using complicated means. In addition, by using a simple circuit configuration that oscillates with a period due to the propagation delay of the amplifier, the appropriate range is determined by the resistance ratio of the first resistor that sets the comparison voltage voltage and the detection resistor, and is stable. Range is unaffected by amplification and without mechanical switches.
It can automatically display warnings for appropriate or inappropriate exposure and camera shake, and also display it when the exposure is appropriate.
Since there is no need to rely on manual switching operations as in the past, all kinds of inconveniences caused by this can be solved, so the practical effects are extremely large.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an example of a conventional exposure warning circuit; Figure 2 is a circuit diagram showing an example of a conventional exposure warning circuit;
The figure is a circuit diagram showing one embodiment of an exposure warning circuit according to the present invention. FIGS. 3 to 8 are circuit diagrams showing other embodiments of the present invention. PD...Photovoltaic element, Ru,
RO...Resistance, VR...Reference voltage source,
A...Amplifier, D1-D3...Diode, Lu, LO...Exposure warning display element, VR
...Comparison voltage source, Cc...Capacitor, SW...Switch.

Claims (1)

[Claims] 1. A device having a first input terminal to which a comparison voltage is applied, a second input terminal to which a detection voltage is applied, a first output terminal, and a second output terminal, wherein the input potential of the first input terminal When is higher than the input potential of the second input terminal, the first output terminal becomes conductive and the second output terminal becomes non-conductive, and when the input potential of the first input terminal is lower than the input potential of the second input terminal, the second output terminal becomes conductive. Continuity 1st
an amplifier whose output terminal is non-conductive; a comparison voltage source that supplies the comparison voltage to a first input terminal of the amplifier; and a first resistor connected between the second input terminal and the second output terminal. , a detection resistor connected to the first resistor and supplying a voltage corresponding to the brightness of the subject to the second input terminal in cooperation with the first resistor depending on the output state of the amplifier; a first display element connected to the second display element; and a second display element connected to the second output terminal, the potential of the first input terminal to which the comparison voltage is applied and the first resistor and the detection resistor The amplifier compares the detected voltage of the second input terminal, which is determined by the above, and if the value is not appropriate, either the first display element or the second display element is turned on, and if the value is proper, the amplifier The detected voltage at the second input terminal, which changes depending on the output states of the first and second output terminals, causes the amplifier to oscillate at a propagation delay period of the amplifier, causing the first and second display elements to alternately blink. An exposure warning circuit characterized by: 2 It has a first input terminal to which a comparison voltage is applied, a second input terminal to which a detection voltage is applied, a first output terminal, and a second output terminal, and the input potential of the first input terminal is equal to that of the second input terminal. When the input potential of the first input terminal is higher than the input potential, the first output terminal becomes conductive and the second output terminal becomes non-conductive. When the input potential of the first input terminal is lower than the input potential of the second input terminal, the second output terminal becomes conductive and the first output terminal becomes conductive.
an amplifier whose output terminal is non-conductive; a comparison voltage source that supplies the comparison voltage to a first input terminal of the amplifier; and a comparison voltage source connected between the second input terminal and the second input terminal at least during photometry. a first resistor; a detection resistor connected to the first resistor that cooperates with the first resistor to supply a voltage corresponding to the brightness of the subject to the second input terminal depending on the output state of the amplifier; a charging capacitor connected in series with the resistor; a switch that short-circuits the capacitor during photometry, releases the short-circuit of the capacitor in synchronization with shutter opening, and short-circuits the detection resistor; and a switch connected to the first output terminal. a first display element and a second display element connected to the second output terminal, the first display element to which the comparison voltage is applied;
The potential of the input terminal and the detection voltage of the second input terminal determined by the first resistor and the detection resistor are compared by the amplifier, and if the potential is not appropriate, the potential of the first display element and the second display element are compared. the amplifier is caused to oscillate at a propagation delay period of the amplifier by the detection voltage at the second input terminal which changes depending on the output states of the first and second output terminals at an appropriate value; 1st and 2nd
An exposure warning circuit characterized in that the display elements of are made to blink alternately.