JPH0151170B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data imprinting device for a camera using a liquid crystal display device.

2. Description of the Related Art In recent years, data imprinting devices have been put into practical use that automatically record photographic data such as the date and time on a film at the same time as the photograph is taken, using an electronic clock having a liquid crystal display device.

The power source for this type of data imprinting device is generally provided separately from the power source for the camera body.
A button-type silver battery or a button-type lithium battery is used as a power source for an electronic watch using a liquid crystal display device.Although the lifespan of lithium batteries in particular is quite long, lasting several years or more, the voltage of the battery decreases at the end of its life. When the amount of light transmitted through the liquid crystal decreases, if you continue to use the battery without noticing, the data image recorded on the film will become unclear and difficult to read.

Conventionally, the lifespan of a battery is detected using a semiconductor device, e.g.
Electrical detection methods such as using the threshold voltage of MOS transistors are common, but such detection methods have large variations in the threshold voltage of semiconductors, and require the use of external adjustment elements to set the desired detection voltage. In addition, a notification means is required to display the results detected in this way. Figure 1 is a block diagram showing an example of a conventional power battery detection method, where E represents a power battery, R ₁ and R ₂ constitute a resistor voltage divider circuit, and the midpoint is connected to the gate of a MOS transistor inverter M. The midpoint potential of R ₁ and R ₂ is
When the voltage drops below the gate threshold voltage of the MOS transistor, the LCD (liquid crystal display) driver
It is configured to display a warning.

Such electrical detection means requires (i) an increase in the circuit scale for electrical detection, and (ii) installation of a means for notifying the electrical detection results.

The present invention relates to a liquid crystal display device (hereinafter referred to as LCD) for external display.
In a data imprinting device for a camera that uses two LCDs, an internal imprinting LCD and an internal imprinting LCD, the photographer can easily use the external display LCD without using a power supply voltage detection device with a complicated configuration as described above. It is an object of the present invention to easily check the power supply voltage and to prevent failures in data imprinting due to a drop in the power supply voltage.

In the present invention, for this purpose, LCDs with different characteristics are used for display and imprinting, and an LCD for external display is used.
The driving threshold level of the LCD was set higher than that of the LCD for internal projection. This allows the person taking the camera to know about problems with data imprinting, such as when the characters displayed on the external display LCD become faint or difficult to see.

Embodiments of the present invention will be described below with reference to the drawings.

2 and 3 are rear views of a camera equipped with a data imprinting device to which the present invention is applied, with FIG. 2 showing the back cover in a closed state and FIG. 3 showing the back cover in an open state.

In the figure, 1 is the back cover of the camera, 2 is a reflective LCD that displays the imprint data set by the electronic clock circuit on an external monitor, and 7 is a film pressure plate.
Reference numeral 8 denotes a transmissive type LCD for imprinting that displays imprint data, which is illuminated by a light source (not shown), and the transmitted light passes through an opening 7a provided in the pressure plate 7 to imprint data from the back side of the film. ing.
3, 4, and 5 are switches for calibrating the data, and 6 is the sensitivity of the film used (or the color of the subject).
to set the lighting time of the light source lamp according to the
It is an ASA changeover switch.

FIG. 4 shows an electric circuit of the data imprinting apparatus shown in FIGS. 2 and 3. Components that are the same as those in FIGS. 2 and 3 are given the same numbers, and their explanations will be omitted.
In Figure 4, E ₁ is the power battery on the camera body side,
SW ₁ is a switch that is linked to the camera's shooting operations. E ₂ is the power battery for the data imprinting circuit installed on the back cover of the camera, and 10 is for data imprinting.
LSI, L indicates a light source lamp.

When the switch SW ₁ is closed by the shutter release, the potential V ₁ changes from a low level to a high level due to the resistor R, and a signal for imprinting is taken in by the trigger input terminal TRI (IN) of the LSI 10. It remains at a high level for a certain period of time determined by the selection of the ASA selector switch 6, the transistor Q is turned on, and the lamp L is lit.
As a result, data is recorded on the film using the light transmitted through the imprinting LCD 8.

FIG. 5 is a diagram showing the relationship between the LCD drive voltage and the amount of light reflection (or amount of light transmission) in the present invention. Curve A shows the light reflection amount characteristic curve with respect to the drive voltage of the LCD 2 for external monitor display; B shows a light transmission amount characteristic curve with respect to the driving voltage of the data imprinting LCD 8.

In the figure, the drive voltage level at the point where the reflected light amount is 10% of the saturated reflected light amount of the external display LCD, that is, the point where the reflected light amount is small and the display becomes thin and difficult to see, or almost invisible, is the threshold voltage (Vth ₁ ).
10 for the saturated transmitted light amount of the LCD for imprinting.
The drive voltage level at the point where the transmitted light amount is % is shown as the threshold voltage (Vth ₂ ).

As can be seen from the figure, when the drive voltage drops below the threshold voltage (Vth ₁ ) of the external display LCD, the
The light transmission amount of the LCD begins to decrease rapidly, and at this time, the display on the external display LCD becomes so thin that it becomes almost invisible, allowing the camera user to know that the battery voltage has decreased.

FIG. 6 is a diagram showing the discharge characteristics of the power supply battery for data imprinting, and shows that the battery voltage gradually decreases over time and rapidly decreases from around _VA .

The threshold voltage shown in FIG. 5 may be set approximately in this vicinity, that is, V≈Vth ₁ , taking into consideration the reduction in lamp light intensity due to voltage drop.

V _B indicates the battery potential at which the discharge of the battery progresses and it becomes impossible to display not only the LCD for external monitor display but also the LCD for imprinting.

As mentioned above, the present invention uses an LCD for external monitor display.
By setting the driving threshold level of the internal imprinting LCD higher than the driving threshold level of the internal imprinting LCD, the user can control data imprinting based on the visibility of the external display LCD without providing a special battery voltage detection means. This has the advantage that it is possible to judge whether or not the data is imprinted, and to replace the battery at an appropriate time, thereby providing an inexpensive and reliable data imprinting device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional example of a power supply voltage detection device, FIGS. 2 to 6 show embodiments of the present invention, FIG. 2 is a rear view of a camera equipped with the device of the present invention, and FIG. The figure also shows the rear view with the back cover open, Figure 4 shows the electric circuit diagram of the data imprinting device, and Figure 5 shows the relationship between the driving voltage of the liquid crystal display device and the amount of light transmission or light reflection. FIG. 6 is a diagram showing the discharge characteristics of the battery. 1: Camera body, 2: Liquid crystal display device for external display, 8: Liquid crystal display device for imprinting, 10: LSI for data display, E ₂ ; Power supply battery for imprinting device, L: Light source for imprinting.

Claims (1)

[Claims] 1. A power supply battery, a data imprinting liquid crystal device driven by the power supply battery, and an external display liquid crystal device having a higher driving threshold level than the data imprinting liquid crystal device driven by the power supply battery. A camera data imprinting device characterized by comprising: