JPS5952372B2 - Exposure warning circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exposure warning circuit that warns a photographer of appropriate or inappropriate exposure, camera shake, etc. in a camera. Concerning unaffected exposure warning circuits.

A conventional circuit of this type is shown in FIG.
1Nb and first and second output terminals VOa, VOb, compares the first input V, Na and the second input Nb,
If lNb>VlNa, the first output V.

a off, second output V. b is turned on, and VlNb is turned on.
<V, Na, the first output V. a on, second output V. b is configured to turn off. and the first
The input terminal VlNa of is connected to the positive terminal + of the power supply via a resistor Ra, and is grounded via a resistor Rb. Here, resistors Ra and Rb are bleeder resistors. Further, the second input terminal VlNb is connected to the positive terminal +V of the power supply via a photoconductor LEC such as cadmium sulfide Cds whose resistance value changes depending on the light from the subject, and also to a switch for switching an indicator light, which will be described later. and grounded through a resistor in series. LO is an indicator light that displays overexposure, Lu is an indicator light for camera shake warning, SW is an interlocking switch for switching the indicator lights LO and Lu, one movable contact is connected to the positive terminal +V of the power supply, and the fixed contact a side is connected to one end of the indicator light LO, and the fixed contact b side is connected to one end of the indicator light Lu. The other ends of the indicator lights Lu and LO are the first and second output ends V of the amplifier A. a and VOb, respectively. The other movable contact of the interlock switch SW is connected to the photoconductor LEC, and this common connection point is connected to the second movable contact of the amplifier A.
The fixed contacts A and b are connected to the input terminal VlNb of the circuit, and the fixed contacts A and b are grounded via resistors RO and Ru, respectively. In a circuit with such a configuration, the first input terminal VlN of amplifier A
The voltage applied to a is used as a comparison voltage, and the second input terminal 1N
If a voltage to be determined determined by the photoconductor LEC and the resistors RO and Ru is applied to b and the interlocking switch SW is operated, when the switch is closed to the a side, VlNb>V, Na
Then, as mentioned above, the first output V of amplifier A.

a is off, second output V. b turns on and the indicator light LO
lights up to warn of overexposure. Further, when the interlocking switch SW is closed to the b side, the first output of the amplifier A is V if VlNb<V, Na. a is on, second output VO
b is turned off, the indicator light Lu lights up, and the photographer is warned that the shutter speed is longer than the camera shake limit. However, such an exposure warning circuit has the disadvantage that no display is made when the exposure is appropriate, which makes the photographer feel uneasy.

Further, it is inconvenient because it requires manual switching operation, and an interlocking switch must be used. In other words, it is necessary to configure the lamp circuit after configuring the check circuit represented by the resistors RO and Ru; if the order is reversed, the check will be performed even momentarily before configuring the check circuit, which may cause erroneous lighting. Therefore, it has the disadvantage that it is mechanically complex and uneconomical. In order to eliminate these drawbacks, a circuit that does not use a switch system has been proposed, as shown in FIG.

In Fig. 2, the same parts as in Fig. 1 are given the same reference numerals.
The explanation will be omitted. In the figure, Rl and R2 are resistors, C1 is a capacitor, and resistor R1 is the first input terminal Vl of amplifier A.
Na, the indicator light Lu and the first output V of the amplifier A. The capacitor C1 is connected between the first input terminal VINa, the indicator light LO and the second output terminal V. b, the resistor R1, the capacitor C1, the first
A common connection point of the input terminal VlNa of is connected to the resistors Ra2:Rb via the resistor R2. Note that +3 indicates the positive electrode side of the power source. Then, this circuit sets the voltage ratio determined by the photoconductor LEC and the variable resistor RO as the second input VlNb of the amplifier A, and if VlNb>Na, the second input of the amplifier A
output V. b is on, the first output V. a is turned off,
The indicator light LO lights up to warn the photographer of overexposure. The first input VlNa at this time is expressed as follows, where VA is the voltage determined by the resistance ratio of the resistors Ra and Rb.

However, the resistance values of the resistors Ra and Rb are so small that they can be ignored compared to the resistors Rl and R2. Also VlNb
<VlNa, the first output VOa of amplifier A is on;
The second output VOb is turned off, and the indicator light Lu lights up to warn that the camera shake is above the limit.

At this time, in the range of the first input V1, a, the resistance Rl
, R2 and capacitor C1, the first and second outputs 0a and V0b of amplifier A are alternately turned on and off, and both indicator lights Lu and LO light up, indicating that the exposure is correct. inform the person. However, in such an exposure warning circuit, the resistors Ra, Rb, Rl,
It is assumed that the resistors R1 and R2 do not affect the voltage VA based on the assumption that R2.

For this purpose, a considerably large current must be passed through the voltage dividing resistors Ra and Rb, which has the disadvantage of increasing power consumption. Also, the first input VlNa of amplifier A is Ra
, Rb, Rl, and R2 to set the determination level, it has a drawback of low accuracy. 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 determine an appropriate range by a simple circuit configuration, to achieve stability, and to improve amplification. To provide an exposure warning circuit which does not affect the appropriate range depending on the temperature, has low current consumption, improves accuracy by setting a judgment level with a small number of parts, and has both an exposure check function and a power supply voltage checker function. There is a particular thing.

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 voltage to be determined 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 when 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 is conductive and whose first output terminal is non-conductive; a first resistor connected between the first input terminal and the first output terminal of the amplifier; a parallel circuit of a second resistor and a first capacitor connected between the two output terminals, and first and second exposure warning display elements connected to the first and second output terminals, respectively; The amplifier compares the potential of the second input terminal to which the voltage to be determined is applied and the comparison voltage of the first input terminal determined by the first and second resistors, and if the voltage is not appropriate, the potential of the first input terminal is Either the exposure warning display element or the second exposure warning display element is turned on, and at an appropriate value, the first and a second exposure warning display element are displayed by blinking alternately, and the present invention also provides a first display element connected to the first output terminal of the amplifier via a resistor; A second capacitor connected in parallel to the first display element, a second display element connected to the second output terminal of the amplifier via a fourth resistor, and a second display element connected in parallel to the second display element. and a third display element connected between the first display element and the second display element via a fourth capacitor, to which the voltage to be determined is applied. The potential of the second input terminal and the comparison voltage of the first input terminal determined by the first and second resistors are compared by the amplifier, and if the voltage is not appropriate, the potential of the first display element and the second display element are one of the first and second output terminals is turned on, and the comparison voltage of the first input terminal changes at an appropriate value depending on the output states of the first and second output terminals of the amplifier, causing the amplifier to oscillate. The display element is turned off and the third display element is turned on.

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 3 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 two inputs VlNa,
vlNb and the first and second two outputs V whose outputs are inverted and opposed depending on the input conditions. a, VOb, and the voltages VlNa, vl applied to the two input terminals
Nb is compared, and if VlNb≧VlNa, the first output V
. a off, second output V. b is turned on, and VIN
If b≦VINa, the first output VOa is turned on and the second output VOb is turned off. The first input terminal VlNa is connected to the first output terminal V through the resistor R3.
. a and a second output terminal V through a parallel circuit of a capacitor C2 and a resistor R4. b, and the second input terminal VlNb is connected to the connection point of a photoconductor LEC such as cadmium sulfide Cds whose resistance value changes depending on the incident light flux and a variable resistor RO, so that the voltage to be determined is applied. It is composed of Here, the photoconductor LEC and the resistance R
O is connected in series to the power supply. On the other hand, amplifier A
The first and second output ends V of. a and VOb are connected to the positive electrode +VB of the power source via exposure warning display elements (hereinafter referred to as indicator lights) Lu and LO, respectively. Next, the operation of the embodiment shown in FIG. 3 will be explained.

Now, the input voltage V applied to the two input terminals of amplifier A.
If Na and vlNb are VlNb≧1Na, then the second output V. Since b is on and the first output VOa is off, it is the second output. b is the ground potential and the first output V.
a becomes the power supply potential, and current flows through the path +VB→R3{:→ground. The potential of the first input VlNa changes over time according to equation (1).

Here, K1 is a constant. If t=ω is smaller than VlNb, the state of VlNb≧VlNa is maintained, and the indicator light LO continues to light up, informing the photographer that the exposure is excessive.

- - - R4 Next, the above formula (2) VlNa=R3+R4. vB is VIN
If it is larger than b, then VlNb<VlNa and the output is V.

a, Ob are inverted and the first output V. a is turned on and the second output V. b is turned off. Here, since ``when the output is inverted is when 1Na=VINb'', the capacitor C2 is charged with the voltage of the second input VINb. and a first output V. a is the ground potential, and the second output V. b becomes the power supply potential, and at this moment the first inputs V, N
a is VB+V, Nb. And the current is VB →
Flows through the path of Go → R3 → Ground, and the first input Vl
Na changes over time according to equation (3).

Here K2 is a constant. And at t=o 1Na=VB
+VlNb, so.

t=ω, that is, VlNa=den♀zonoV8 is the second input 1N
If it is smaller than b, the output is V. a and VOb are inverted and return to their initial states. This inversion occurs when VlNa=VlNb, so capacitor C2 has VB-VlN.
The voltage of b is charged. Therefore, in the above equation (1),
This is because when t=o, VlNa=(VB-VlNb).

If this is the case, the circuit shifts to an oscillating state, and the indicator lights Lu, L
O blinks alternately, indicating that the exposure is appropriate.

Here, the blinking cycle can be arbitrarily set by selecting the capacitor C2, from a range where the photographer perceives the lights to be lit simultaneously to a range where the photographer perceives the lights to be lit alternately. R
3 And if R3+R48〉VlNb, then VlNa
>The VlNb state is always maintained and the indicator light Lu lights up, indicating that the shutter is longer than the camera shake limit.
．． , R4 is displayed to warn the photographer of camera shake.

Also, if R3+R4VB<VlNb, then V, Na
<The state of VlNb is always maintained and the indicator light is L. lights up to warn of overexposure. 4 and 5 are explanatory diagrams of the operation of FIG. 3 showing the state of the above operation, and FIG.
This shows the change in the potential of the input VlNa, and the fifth
The figure shows the lighting area of the indicator lights LO and Lu with respect to the second input VlNb.

FIG. 6 is a circuit diagram showing another embodiment of the present invention. 6th
In the figure, the same reference numerals as in Figure 3 indicate corresponding parts.
Cu is a capacitor connected in parallel to the indicator light Lu, Ru
is a resistor connected in series to the parallel circuit of indicator light Lu and capacitors Cu and l, and Cu and ru form a filter circuit when the circuit oscillates. CO is a capacitor connected in parallel to indicator light LO, RO is a resistor connected in series to the parallel circuit of indicator light LO and capacitor CO, and CO and rO constitute a filter circuit when the circuit oscillates. ing. Lk is the third indicator lamp, Ck is a capacitor connected in series with the third indicator lamp Lk, and these are the first output terminal V of the amplifier A. a and the second output end. b, and constitutes a filter circuit that blocks the DC component of the output of the amplifier A, or its equivalent part, and passes the AC component. In the circuit configured in this way, first, VlNb
>In the case of Todoroki V8, indicator light LO is lit, indicator lights Lk, L
u turns off, and the indicator light LO lights up to warn of overexposure.

In the following case, the circuit oscillates, and in this case the indicator light L
O and Lu go out, the indicator light Lk lights up, and the exposure is appropriate R4
Show that it is true.

If VlNb<R3+RVB, the indicator light Lu lights up, indicating that the shutter length is longer than the camera shake limit, and giving a camera shake warning. At this time, the indicator lights LO, L
u are both turned off. If you describe this in detail, the indicator light L
Capacitors Cu and CO are inserted in parallel to u and LO, respectively, and when the circuit is oscillating, they act as a filter and do not turn on the first and second indicator lights Lu and LO, but turn on the third indicator light Lk. Turn it on. Conversely, indicator light Lu or indicator light L
When only O is lit, the direct current is blocked by the capacitor Ck inserted in series with the third indicator lamp Lk, and the third indicator lamp Lk is not lit. With this configuration, the first
, the second and third indicator lights Lu, LO, and Lk have different emission colors, for example, the first indicator light Lu that indicates the camera shake limit.
By changing the coloring of the display to yellow, the second indicator light LO indicating overexposure to red, and the third indicator light Lk indicating appropriate exposure to green, it is possible to provide convenience to the user. FIG. 7 is a circuit diagram showing still another embodiment of the present invention, in which indicator lights Lu, L
This is an example of a case where a switching transistor is provided in series with O, and the power supply voltage is checked at the same time, or the power supply voltage check and the shutter operation display function are combined.

In FIG. 7, the same parts as in FIG. 3 are given the same reference numerals, and their explanations will be omitted. In the figure, Tr is a switching transistor, the emitter is connected to the positive pole +3 of the power supply, the collector is connected to the indicator lights Lu and LO, and the base is the connection point between resistors R5 and R6 connected in series to the power supply. It is connected to the. In this way, the transistor Tr is connected in series with the indicator lights Lu and LO, and the power supply voltage is detected by the resistors R5 and R6. First, when the power supply voltage is sufficient, the transistor Tr is turned on and operates in the same manner as shown in FIG. 3, and the indicator lights Lu and LO are turned on to detect that the power supply voltage is sufficient. At the same time, you can know whether exposure is appropriate or not. Next, when the power supply voltage decreases, the transistor Tr turns off, and accordingly, the indicator lights Lu and LO do not light up, making it possible to detect a shortage of the power supply voltage. Here, the film sensitivity ASA, aperture, etc., which are essential conditions for a camera, are achieved by appropriate setting interlocking means of the photoconductor LEC or the variable resistor RO connected in series with the photoconductor LEC. be able to.

In addition, in the case of aperture-priority shutter speed control, the time constant Cds (not shown) and the photoconductor LEC are shared or used together in a certain relationship, and in the case of shutter speed priority, the time constant resistor (not shown) is used. It goes without saying that it is only necessary to link the variable resistor RO and the variable resistor RO in a certain relationship. FIG. 8 is a circuit diagram showing another embodiment of the present invention, showing an example in which the indicator lamp has both an exposure warning function and a shutter operation display function.

In Fig. 8, the same reference numerals as in Fig. 7 indicate the same elements and the same functions. A series circuit of R5 and resistor R6 is connected in parallel. In a circuit configured in this way,
Since one end of the resistor R6 is connected to the output of the shutter control circuit S-C, Tr is connected while the shutter is open.
is turned on, both or one of indicator lights Lu and LO lights up, giving a warning corresponding to the lighted lamp. Then, when the shutter control circuit S-C is turned off and the shutter is closed, the transistor Tr is turned off and the indicator light goes out, and the indicator lights Lu and LO can have the functions of exposure warning and shutter operation display. . In each of the above embodiments, the indicator light Lu has been described as an indicator light that warns that the camera shake is above the limit, but it can also be used as an underexposure indicator and used in a shutter speed priority readout system.

As is clear from the above explanation, according to the present invention, unlike conventional circuits, there is no need to flow an extra large current through a bleeder resistor, and the exposure warning determination is determined by only two resistors. It is possible to reduce power consumption compared to the above circuit and also to provide a more accurate exposure warning, so the practical effect is extremely large.

In addition, the photographer can use a capacitor to arbitrarily set the perception of both indicator lamps lighting up or blinking simultaneously, and can also check the exposure and power supply voltage at the same time using the exposure warning display element. It is also extremely effective in that it can also serve as a shutter operation display.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing a conventional exposure warning circuit, FIG. 3 is a circuit diagram showing an embodiment of the exposure warning circuit according to the present invention, and FIGS. 4 and 5 are circuit diagrams showing the operation of FIG. 3. The explanatory drawings and FIGS. 6 to 8 are circuit diagrams showing other embodiments of the present invention. A...Amplifier, RO...Variable resistor, R
3~R6...Resistor, C2, Ck...Capacitor, LEC...Photoconductor, Lu, LO,
Lk...Exposure warning display element.

Claims (1)

[Claims] 1. A first input terminal to which a comparison voltage is applied, a second input terminal to which a voltage to be determined is applied, a first output terminal, and a second input terminal to which a comparison voltage is applied.
an output terminal, and when the input potential of the first input terminal is higher than the input potential of the second input terminal, the first output terminal conducts and the second output terminal conducts.
An amplifier whose output terminal is non-conductive and whose second output terminal is conductive and whose first output terminal is non-conductive when the input potential of the first input terminal is lower than the input potential of the second input terminal; and a first input of the amplifier. a parallel circuit including a first resistor connected between the terminal and the first output terminal; a second resistor and a first capacitor connected between the first input terminal and the second output terminal; the first and second exposure warning display elements connected to the first and second output terminals, respectively, and the potential of the second input terminal to which the voltage to be determined is applied and the first and second exposure warning display elements;
The comparison voltage of the first input terminal, which is determined by the resistance, is compared by the amplifier, and if the voltage is outside the proper range, one of the first exposure warning display element and the second exposure warning display element is turned on to determine the proper value. is characterized in that the first and second exposure warning elements are displayed by blinking alternately based on the comparison voltage of the first input terminal that changes depending on the output states of the first and second output terminals. exposure warning circuit. 2. A first input terminal to which a comparison voltage is applied, a second input terminal to which a voltage to be determined is applied, a first output terminal, and a second input terminal to which a comparison voltage is applied.
an output terminal, and when the input potential of the first input terminal is higher than the input potential of the second input terminal, the first output terminal conducts and the second output terminal conducts.
An amplifier whose output terminal becomes non-conductive and whose second output terminal becomes conductive and whose 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; and a first input of the amplifier. a parallel circuit including a first resistor connected between the terminal and the first output terminal; a second resistor and a first capacitor connected between the first input terminal and the second output terminal; a first display element connected to the first output terminal via a third resistor; a second capacitor connected in parallel to the first display element; and a second capacitor connected to the second output terminal via a fourth resistor. a second display element, a third capacitor connected in parallel to the second display element, and a fourth capacitor connected between the first display element and the second display element. a third display element, the amplifier compares the potential of the second input terminal to which the voltage to be determined is applied with the comparison voltage of the first input terminal determined by the first and second resistors. When the value is not appropriate, either the first display element or the second display element is turned on, and when the value is not appropriate, the first display element is turned on.
and causing the amplifier to oscillate with a comparison voltage at the first input terminal that changes depending on the output state of the second output terminal, thereby turning off the first and second display elements and lighting up the third display element. An exposure warning circuit characterized by: