DE3433564A1 - Electronic circuit for exposure measurement and shutter control in photographic cameras - Google Patents

Abstract

An electronic circuit for exposure measurement and shutter control of photographic cameras is described. This circuit has an object light-density measuring part, an oscillator, a binary counter, magnets, which open and close the shutter, and a control logic, which connects all these components to one another. By activating the control logic, first of all the object light density is measured and, during the measuring time, the duration of which is dependent on the object light density, the pulses of the oscillator are counted into the binary counter. At the end of the measuring time, therefore, the counter has been set to a state proportional to the light density. This state can be maintained over a prolonged period of time, ie. the measurement result can be stored. In the following exposure, the shutter is opened directly and, in addition, the oscillator connected to the counter, the counter at the same time being switched over to downward counting. The oscillator pulses counted into the counter, as it were, during the exposure measurement are then counted out again and, when the counter reading has reached zero again, a closing signal is sent to the shutter-closing magnet.

Description

Electronic circuit for exposure

measurement and shutter control in photographic cameras the The invention relates to a circuit for measuring, storing and displaying the exposure time as well as for controlling the shutter of a photographic camera as a function from the stored exposure value.

Use known circuits for exposure measurement and control as a measuring circuit for the lens luminance usually an arrangement of a photodiode, a logarithmic amplifier and a capacitor as well as other electronic components for storage of measured values and time calculation. Thereby the current of the photodiode, the can vary in the range of approx. 5 powers of ten1 compressed by taking the logarithm and converted into a voltage which is stored as a measured value in the capacitor will.

Such circuits, which are also still in a manner known per se process further exposure parameters (e.g. film speed and aperture) a high level of expenditure on electronic components.

In particular, to compensate for the temperature change, the logarithmic or de-logarithmizing amplifier and other fault currents special adjustment stages with variable resistances required.

The invention is based on the object of an electronic circuit to create the specified type, compared to similar circuits according to the prior the technology is simpler in its structure and thus lighter and cheaper can be produced, and which also fulfills other functions that are required for the circuits can only be implemented according to the state of the art with a large amount of circuitry. Such further functions are e.g. the simple but reliable and stable storage the measured exposure value and the display of the expected exposure time in digitized form by means of a series of light-emitting diodes.

This object is achieved by a circuit which the claim 1 has specified features. Special configurations and special embodiments the circuit are listed in the subclaims.

An essential element of the invented circuit is a control logic, on the one hand an oscillator and a binary counter to determine the exposure time and on the other hand to control the shutter according to the set exposure time the binary counter with Driver stages and magnets for the camera shutter connects. This control logic can be switched from the idle state into two operating states, namely once in the "Measure" operating state. In this state it connects the oscillator in such a way with the binary counter that the oscillator pulses in the counter are counted. An RC circuit for measuring the object luminance is available and is also switched on when the "Measure" mode is switched on. This circle determines the duration of the count-in process by the capacitor voltage is fed to a comparator, which is given a reference voltage. With equality The comparator sends a signal to the capacitor voltage and reference voltage Control logic, which then stops the count-in process.

The control logic can then be switched to the "Exposure" operating state.

In this state it connects the binary counter and two driver stages for two magnets to open and close the shutter and the oscillator in such a way, that the shutter opening magnet is activated immediately, that the binary counter with the Frequency of the oscillator counts down to zero, and that the shutter-closing magnet is activated when the counter has reached zero.

It is thus controlled by the control logic, initially one of the exposure times Proportional number of pulses are counted into the binary counter and used for control the exposure, i.e. counted out of the counter for shutter control. It is essential that the counted-up state of the binary counter is almost arbitrary can be sustained for a long time, i.e. the exposure time can be in a simpler Way to be stored over a longer period of time.

This basic principle can be modified and further developed that allow further exposure factors, such as film speed and aperture to take into account. Means can also be connected to the binary counter be, e.g. a row of LEDs, on the basis of which the measured and stored Exposure time can be read, and finally measures can also be taken which allow the "Measure" operating state to be compared to the "Exposing" state to be shortened in time. This can be done, for example, by adding two Oscillators are used, a first oscillator for "measuring" and a second oscillator for "exposure", with the oscillator for measuring with is operated at a higher frequency. This makes the measurement time versus the exposure time abbreviated. In addition, there is the advantage that the measuring RC circuit used capacitor can be smaller, precisely in the ratio smaller, in which the frequency of the measuring oscillator is higher than that of the exposure oscillator.

This basic principle and such modifications and other features of the invention are explained in more detail with reference to the attached block diagram.

As shown in the figure, the measuring circuit is made up of the charging capacitor 1, the photoreceiver 2 and the voltage comparator 4 are formed. With the potentiometer 3, a variable reference voltage can be set on the comparator 4. Of the In the rest position of the circuit, transistor 5 is conductive and prevents charging of the capacitor 1.

If switch 6 is now moved from rest position 7 to position 8 ( = Measuring) moves, the control logic 10 generates a signal that the transistor 5 blocks. At this moment, the charging of the capacitor 1 by the photocurrent begins of the photo receiver 2.

At the same time, the control logic 10, the frequency of the oscillator 11 switched through to the binary counter 17. While the capacitor is charging 1 up to the switching threshold of the comparator specified by the potentiometer 3 4 are now the pulses of the oscillator frequency of the oscillator 11 in the counter 17 counted. If the switching threshold of the comparator 4 is reached, its output switches to, and the control logic 10 blocks the input of the counter 17 for the frequency of the Oscillator 11.

At this moment the measurement is finished and the counter content is proportional to the measured charging time of the capacitor, i.e. the exposure time. The meter start is now displayed with the help of LEDs LD 18 - 22. In addition becomes the highest value binary digit of the counter set by the pulse train coded out and displayed with an assigned light-emitting diode 18-22. All inferior Positions are suppressed by appropriate logical links.

In this way it is achieved that in each case a light emitting diode from the Row lights up and the associated exposure time from the standardized time series indicates.

However, it is also possible to use the next lower-order digits of the Counter to evaluate and intermediate values of the standardized exposure times thereby indicate that two adjacent LEDs light up at the same time.

The measured exposure time can now be stored in counter 17 for so long how the switch 6 remains in position 8.

The measurement can be repeated by turning switch 6 in the position 7 is switched back and then moved back to the position 8 will. As a result, the control logic 10 initially clears the content of the counter 17 and discharge the capacitor 1 with the transistor 5. Then the new measurement can be made take place.

Should now be a. With the measured and stored exposure time Take place, switch 6 is moved from position 8 to position 9 ( = Exposure) moved. As a result, the control logic 10 firstly sends a signal the driver stage 23 released, which in turn turns on the magnet 24. This Magnet controls the opening process of the shutter (not shown) so that the Exposure begins.

Second, the control logic 10 to expose the counter 17 on Switched down counting and with the frequency of the oscillator 14 down to zero counted back. The time required for this corresponds to the effective exposure time. When the count reaches zero, the control logic sends a signal to the Output driver stage 25, which in turn turns on magnet 26. This magnet controls the closing of the shutter so that the exposure is terminated.

The frequencies of the two oscillators can be chosen differently will. In general, the frequency of the measuring oscillator 11 is set higher than that of the exposure oscillator 14. This means that the measuring time E.g. only 1/10 to 1/100 of the exposure time, so that by measuring it is practical there is no delay for the exposure.

The control of the measurement and exposure range could, however each with only one oscillator with a fixed frequency or with a switchable or shared frequency.

The frequency of the measuring oscillator 11 can be a function of one of the Exposure parameters film speed or aperture can be changed. In the illustrated Circuit is the frequency of the oscillator 11 through the resistor 12 and the capacitor 13 and can be determined by varying the resistance 12 in a wide range to be changed. The exposure parameter entered by this frequency change causes the number of pulses to change while the charging time of the capacitor 1 remains the same in the counter and is displayed accordingly by the LEDs 18-22.

Another exposure parameter can be set by varying the switching threshold of the voltage comparator 4 can be entered using the potentiometer 3, so that with this circuit principle, the input of both exposure parameters solved will. The frequency of the oscillator 14 for counting down the counter 17 during the exposure can only be changed to a small extent. Otherwise the displayed The exposure time no longer corresponds to the effective exposure time.

It is possible, however, by varying the frequency of the Oscillator 14 with the help of potentiometer 15 fine-tune the effective Exposure time. With this, e.g. the scattering of the electrical parameters of the capacitor 1 and the photoreceiver 2 are compensated.

Claims (6)

Claims 1. Electronic circuit for exposure measurement and shutter control in the case of photographic cameras, the object luminance measuring part of which consists of a circuit with a photo receiver, a capacitor and a voltage comparator, wherein charging of the capacitor by the photocurrent up to a predetermined one Switching threshold of the comparator takes place, characterized by the following features: a) there is a control logic (10), which by means of a sequence switch (6-9) Can be switched from a rest position to the "Measure" and "Exposure" modes is, b) an oscillator (11) and a binary counter (17) are connected to the control logic, which are connected to one another in this way when the control logic is switched to the "Measure" state are that the pulses of the oscillator are counted in the counter, c) the control logic is connected downstream of the comparator (4) in such a way that when the capacitor voltage is equal and reference voltage, the "measuring" operating state of the control logic is terminated, d) the control logic is followed by further control elements (23 ... 26), which start or end the open time of the camera shutter when the control logic is through Switching through the sequence switch is transferred to the "Exposure" operating state, whereby e) the components (23, 24) which open the shutter are activated directly are, and the binary counter (17) switched to counting down and in this way is connected to the oscillator (11) that the counter with the frequency of the oscillator counts down to zero and the control logic (10) the components closing the shutter (25,26) turns on when the counter has reached zero. 2. Electronic circuit according to claim 1, characterized in that that two different oscillators (11, 14) are provided for measuring and exposure, of which the oscillator (11) used for measuring works at a higher frequency. 3. Electronic circuit according to one of claims 1 or 2, characterized characterized in that the oscillators (11, 14) of RC circuits (12, 13 ', 15, 16) with variable resistors (12, 15) are controlled, via which the frequency of the oscillators is adjustable. 4. Electronic circuit according to claim 1, characterized in that that with the binary counter (17) a light-emitting diode row (18-22> is connected, the shows the count of the binary counter. 5. Electronic circuit according to claim 4, characterized in that that in each case the most significant binary digit of the counter is indicated by an assigned light emitting diode (LD) is displayed. 6. Electronic circuit according to claim 4, characterized in that that the most significant and the next least significant binary digits of the Counter can be decoded by a corresponding logical link, so that at Intermediate values, the two neighboring LEDs light up at the same time.