JPH08327406A - Backlight control circuit for display device of surveying instrument - Google Patents

Abstract

PURPOSE: To provide a backlight control circuit, for a display device at a surveying instrument, in which it is not required at all to change a circuit constitution even when only a backlight whose number is smaller than the connectable maximum number is connected. CONSTITUTION: An operational amplifier OP1 is provided with a shutdown terminal C1. When a voltage at an H-level is applied to the shutdown terminal C1, the terminal is set to an active state. When a voltage at an L-level is applied to the shutdown terminal C1, the terminal is set to a sleep state. In the sleep state, the output side of the operational amplifier OP1 is set to a high-impedance state. Consequently, a base current is not supplied to a transistor Q1, the transistor Q1 is kept to be turned off, and a collector-to-emitter current does not flow. Thereby, even when a backlight L1 is not connected to the transistor Q1, the operational amplifier OP1 does not run away.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight control circuit for supplying a constant current to the backlight of a display provided in a surveying instrument.

[0002]

2. Description of the Related Art Conventionally, as a surveying instrument for measuring the distance, elevation, etc. of a land, a ranging finder such as a lightwave ranging finder and a goniometer such as an electronic theodolite have been generally used. The light-wave rangefinder measures the distance from a specific measurement point to a measurement target point. The electronic theodolite measures the direction of the measurement target point as a horizontal angle and an altitude angle centered on a specific measurement point. In addition, recently, a total station in which the lightwave distance measuring device and an electronic theodolite are integrally combined has been put into practical use.

In such a surveying instrument, a display is provided to display a surveyed value (distance measurement value, angle measurement value, etc.) obtained as a result of the survey and an operation instruction. A liquid crystal display (LCD) is usually used for this display,
When the surroundings are dark such as at night, a backlight arranged behind the liquid crystal display plate is turned on so that the display content can be read. FIG. 5 shows the configuration of a backlight control circuit unit for driving such a backlight.

The backlight control circuit unit shown in FIG. 5 is configured to supply a constant current to the two backlights L1 and L2 for illuminating the two displays, respectively. In this backlight control circuit unit, operational amplifiers (OP1, OP2) and transistors (Q1, Q2) are provided for each of the backlights L1, L2.
2) and a constant current circuit (constant current sink) composed of resistors (R1, R2) are prepared and mounted on the same circuit board. Each of these constant current circuits operates independently of each other and supplies a constant current to each of the backlights L1 and L2. In this way, the independent constant current circuit is prepared for each of the backlights L1 and L2 so that the operation of one circuit does not affect the operation of the other circuit.

By the way, it is desirable that the indicator of the surveying instrument is installed on the front and the back of the surveying instrument so that it can be operated from the front side and the back side, respectively (both sides are mounted). In many cases, it is often equipped on only one side (mounted on one side). In the case of mounting on both sides, two backlights are required to illuminate the two indicators, respectively.
For one-sided mounting, only one backlight is needed to illuminate one indicator.

However, even if such a double-sided surveying instrument and a single-sided surveying instrument are produced by the same manufacturer, the components of the backlight control circuit unit may be replaced by each surveying instrument from the viewpoint of cost reduction. Is required to be shared in.

[0007]

However, in the backlight control circuit for a plurality of backlights shown in FIG. 5, only one constant current circuit (opamp OP2, transistor Q2, resistor R2) should not be connected to the backlight L2. Then, the output side of this constant current circuit is in a no-load state. Therefore, there is a risk that the operational amplifier OP2 will run away, causing an excessive current to flow and destroying the constant current circuit itself and other circuits. Therefore, the conventional backlight control circuit unit for a plurality of backlights shown in FIG. 5 cannot be used as it is as a backlight control circuit for a single backlight.

Therefore, when the conventional components of the backlight control circuit unit for a plurality of backlights shown in FIG. 5 are used as a backlight control circuit for a single backlight, as shown in FIG. Constituent circuit parts of the constant current circuit on the side not connected (operational amplifier OP2, transistor Q2, resistor R
2) had to be deleted from the circuit board. That is, conventionally, the backlight control circuit unit for a surveying instrument mounted on both sides shown in FIG. 5 and the backlight control circuit unit for a surveying instrument mounted on one side shown in FIG. 6 must be prepared as separate parts. I had to do it. Therefore, in terms of manufacturing, management, and maintenance,
The cost was high.

In view of the above problems, an object of the present invention is that there is no need to change the circuit configuration of the backlight even when only a smaller number of backlights than the maximum number of connectable backlights are connected, and therefore display is possible. It is an object of the present invention to provide a backlight control circuit for a display of a surveying instrument that can be shared by a plurality of types of surveying instruments each having a different number of instruments.

[0010]

In order to solve the above problems, a backlight control circuit for a display of a surveying instrument according to the present invention has a plurality of constant currents provided to supply a driving current to a plurality of backlights. In the backlight control circuit for a display of a surveying instrument comprising a circuit, each of the constant current circuits has a resistor for converting the drive current into a voltage value, and a voltage value and a reference voltage value converted by the resistor, respectively. An operational amplifier having a shutdown terminal for inputting to the input terminal and outputting an output voltage corresponding to both of these voltage values from the output terminal, and switching the impedance state of the output terminal to a high impedance state or a low impedance state according to the applied potential; , The drive current according to the output voltage output from the output terminal of the operational amplifier Gosuru characterized by comprising a transistor (corresponding to claim 1).

[0011]

Embodiments of the present invention will be described below with reference to the drawings. Before giving a detailed description of the embodiments, the concept of each constituent element of the present invention will be described. (Surveyor) The present invention can be applied to all surveying machines such as a rangefinder and a goniometer that can display a surveyed value related to a positional relationship between a surveyed point and a surveyed point. As a rangefinder, it can be applied to a lightwave rangefinder. As a goniometer, it can be applied to an electronic theodolite. Furthermore, the present invention can also be applied to a total station that combines the functions of an optical distance measuring instrument and an electronic theodolite. (Display) A liquid crystal display plate can be used for the display. This liquid crystal display panel is applicable regardless of whether it is a static type or a dynamic type. The backlight for illuminating the display is not necessarily on the back of the display, and may be for illuminating the display from the side of the display. The number of display backlights that can be supplied with power by the display backlight control circuit of the surveying instrument is not limited as long as it is plural, and may be three or more. However, the same number of constant current circuits as this number will be incorporated in the backlight control circuit.

The backlight is a light emitting diode (L
ED), an incandescent lamp such as a wheat ball, or a neon lamp. (Resistance) The resistance is not limited to an element manufactured as a resistor, but includes any element that has a resistance component and that can convert a current value into a voltage value by this resistance component. (Op Amp) This op amp may input the voltage value converted by the resistor to its inverting input terminal and the reference voltage value to its non-inverting input terminal (claim 2). Correspondence).

A reference voltage output from a common reference voltage source may be input to the operational amplifier of each constant current circuit (corresponding to claim 4). By doing so, the drive current supplied to each backlight can be made equal regardless of the voltage of the power source or the like.

All constant current circuits may be mounted on a common substrate (corresponding to claim 5). With this configuration, the backlight control circuit mounted on the common substrate can be treated as one unit.

The internal circuit of the operational amplifier may be configured so that the output terminal is in a high impedance state when the shutdown terminal of the operational amplifier is pulled down to a potential lower than a predetermined threshold value (corresponding to claim 6). . With this configuration, the operational amplifier can be kept in the sleep state and its runaway can be prevented regardless of the capacity of the power supply for applying the potential to the shutdown terminal. (Transistor) The transistor may be a junction transistor or a field effect transistor.

In the case of adopting the above-mentioned constant current sink configuration using the junction transistor, the base is connected to the output terminal of the operational amplifier, the emitter is grounded through the resistor, and the one backlight is provided. The collector is connected to the power supply for the drive current. Then, the emitter voltage may be input to the inverting input terminal of the operational amplifier (corresponding to claim 3).

[0017]

First Embodiment A first embodiment of the present invention will be described below with reference to the drawings. This embodiment shows an example in which a backlight control circuit for a display of a surveying instrument according to the present invention is mounted on a total station equipped with two displays. <Outline of Total Station> FIG. 2 is a view of the total station viewed from the opposite position, and FIG. 3 is a view of the total station viewed from the normal position. As is clear from FIGS. 2 and 3,
The total station is roughly divided into a collimating telescope section 1, a main body section 2, and a base section 3.

The main body 2 has a substantially U-shaped outer shape when viewed from the front. A first indicator 4, a first key input unit 5, and the like are provided on the front surface of the main body 2. Also,
On the back side, the second display unit 6, the second key input unit 7,
Etc. are provided.

The collimating telescope section 1 has a substantially box-shaped appearance that matches the U-shaped concave shape of the main body section 2. The collimation telescope unit 1 contains a collimation telescope for collimating a measurement target. FIG. 2 shows the objective lens 8 of this collimation telescope.
FIG. 3 shows the eyepiece of this collimating telescope. The objective lens 8 is a light-transmitting optical system for transmitting modulated light for light-wave distance measurement, and a light-receiving optical system for receiving return light of modulated light reflected by a prism (corner cube) arranged at a measurement target point. Also serves as a system. The collimation telescope unit 1 detects an emitting device for emitting the modulated light, a light receiving device for converting the return light into an electric signal, and a phase difference between the phase of the modulation at the time of emission and the phase of the return light. The phase difference detection device is also integrally provided. From this phase difference, the oblique distance from the measurement point where the total station is arranged to the measurement target point is calculated.

The collimating telescope unit 1 is axially supported in the U-shaped recess 2a of the main body 2 and is rotatable in the vertical direction. The main body 2 itself is axially supported by the base 3 and is rotatable in a horizontal plane. The relative rotation angle between the collimating telescope 1 and the main body 2 and the relative rotation angle between the main body 2 and the base 3 are detected by encoders (not shown). Therefore, by collimating the measurement target point (the target placed at the measurement target point) with the collimation telescope, the direction of the measurement target viewpoint with respect to the measurement point can be measured.

Further, in the main body 2, various applied survey calculations are performed on the distance measurement data (oblique distance) and the angle measurement data (direction), so that various value-added data (for example, measurement points and An arithmetic processing circuit (not shown) for deriving a horizontal distance and an altitude difference from the measurement target point is built in.

The first display unit 4 and the second display unit 6 display such distance measurement data, angle measurement data, and various value-added data, and distance measurement by an arithmetic processing circuit (not shown) or The operation instruction at the time of angle measurement is displayed.

These first display 4 and second display 6
Is a liquid crystal display panel (LC
D). On the back side of the first display 4 and the second display 6, there are reflectors for reflecting external light and backlights L1 and L that are turned on when the external light is dark.
2 are arranged. <Structure of Backlight Control Circuit> FIG. 1 is a circuit diagram showing the structure of a backlight control circuit for supplying a constant current to each of the backlights L1 and L2. As shown in FIG. 1, this backlight control circuit is provided for each of the backlights L1 and L2.
Two constant current circuits (op amp OP, transistor Q, resistor R) are provided. These two constant current circuits are connected in parallel to the common reference voltage source E1. Further, each constant current circuit is configured to function as a constant current sink that draws a constant current from each power source E2, E3 via each backlight L1, L2. The constituent circuit components of the constant current circuit and their functions will be described below by taking the constant current circuit for the backlight L1 as an example.

The reference voltage source E1 supplies an operational amplifier OP with a reference voltage that determines the amount of constant current supplied to the backlight L1.
This is a circuit component applied to the first non-inverting input terminal. For the reference voltage source E1, for example, a Zener diode that outputs a constant terminal voltage is used.

On the other hand, the power source E2 is a power source for supplying power to the entire total station. Therefore, although illustrated separately in FIG. 1, the power source E2 and the power source E3 for the other backlight L2 are actually the same. The positive electrode of the power source E2 is connected to the anode of the backlight L1 composed of a light emitting diode.

The cathode of the backlight L1 is connected to the collector of the transistor Q1. This transistor Q1 controls the amount of collector-emitter current according to the output voltage value of the operational amplifier OP1 connected to its base. The emitter of the transistor Q1 is grounded via the resistor R1. That is, the transistor Q1 functions as an emitter follower amplifier. The emitter voltage of this transistor is fed back to the inverting input terminal of the operational amplifier OP1.

The operational amplifier OP1 is an operational amplifier IC chip having a shutdown function, and is, for example, LINE.
AR TECHNOLOGY LTC1152 chip is used. That is, this operational amplifier OP1 has a shutdown terminal C1.
And is activated when an H level voltage is applied to the shutdown terminal C1, and enters a sleep state when an L level voltage is applied to the shutdown terminal C1. In this sleep state,
The current supplied to the operational amplifier OP itself is about 1 μA, and the output terminal side is in a high impedance state. When the shutdown terminal C1 becomes floating, this supply current pulls up the voltage of the shutdown terminal C1 to the H level state.

The configuration of the constant current circuit for the other backlight L2 is the same as the configuration of the constant current circuit for the backlight L1 described above (especially, the value of the resistor R2 is the resistance R1.
Since the value is the same as the value of), the description thereof will be omitted.

Of these circuit components, all the backlights L1 and L2 and the power sources E2 and E3 are mounted on the same circuit board B to form a backlight control unit. <Operation of the embodiment> The backlight control circuit shown in FIG. 1 is connected to other circuits in the total station so that the shutdown terminals C1 and C2 of the operational amplifiers OP1 and OP2 are always pulled up to H level.

When using the total station,
When a lighting switch (not shown) is turned on, each operational amplifier O
The reference voltage from the reference voltage source E1 is applied to the non-inverting input terminals of P1 and OP2. On the other hand, in the initial state, since the emitter current does not flow through the transistors Q1 and Q2, the emitter voltage applied to the inverting input terminals of the operational amplifiers OP1 and OP2 is at the ground level. Therefore, in each operational amplifier OP1 and OP2, the voltage difference between the non-inverting input terminal and the inverting input terminal is eliminated, that is, the voltage applied to the inverting input terminal matches the voltage applied to the non-inverting input terminal (reference voltage). So that its output voltage is increased.

Then, the transistors Q1 and Q2 are turned on.
Then, the current is absorbed from each of the power sources E2 and E3. This current (collector current) is applied to each backlight L.
1 and L2 are turned on to illuminate the indicators 4 and 6 from the back side thereof. Also, this collector current is
1 and Q2 are superimposed on the base currents from the operational amplifiers OP1 and OP2 to become emitter currents, and the resistors R1 and
The voltage across the terminals of R2 is increased. That is, each operational amplifier O
The emitter voltage applied to the inverting input terminals of P1 and OP2 is increased.

The emitter voltage is the reference voltage E1.
When each of the operational amplifiers OP1 and OP2 agrees with the above, the output voltage of the operational amplifiers OP1 and OP2 stops increasing, and the transistors Q1 and Q2 always flow a constant collector-emitter current. Even if the collector-emitter current fluctuates for some reason thereafter, this fluctuation appears as a change in the voltage between the terminals of the resistors R1 and R2 (emitter voltage of the transistors Q1 and Q2). The output voltage is automatically adjusted so that the emitter voltage returns to its original value (to match the reference voltage). Therefore, each transistor Q1,
The collector-emitter current of Q2 is restored. In this way, a constant current is constantly supplied to each of the backlights L1 and L2.

Since the value of the resistor R1 on the side of the backlight L1 is the same as the value of the resistor R2 on the side of the backlight L2, even if the voltages of the power sources E2 and E3 are different,
Even if the amplification factors of the transistors Q1 and Q2 are slightly different, substantially the same amount of current flows through the backlights L1 and L2.

On the other hand, when the backlight control unit having the above-described structure is mounted on the one-side-mounted total station (a low-priced total station in which the second display 6 is omitted), the second display 6 Since the backlight L2 for light is removed from the total station, the collector of the transistor Q2 has no load, as shown in FIG. In that case, the shutdown terminal C1 of the operational amplifier OP1 constituting the constant current circuit connected to the backlight L1 is connected to other circuits by being pulled up to the H level, but the backlight is connected. The shutdown terminal C2 of the operational amplifier OP2 on the non-constant current circuit side is connected to another circuit so as to be pulled down to the L level.

Therefore, the constant current circuit connected to the backlight L1 supplies a constant current to the backlight L1 in the same manner as described above, but the operational amplifier OP2 of the other constant current circuit goes into the sleep state. Therefore, the output side of the operational amplifier OP2 is in a high impedance state, and the base current does not flow in the transistor Q2, so that the transistor Q2 remains OFF. as a result,
It prevents the constant current circuit that is not connected to the backlight from flowing an excessive current, and prevents the backlight control circuit unit and other circuits from being destroyed by the excessive current (even in the sleep state. Although a current of about 1 μA is supplied to the operational amplifier OP2, the consumption of unnecessary current can be suppressed to a low level as compared with the case of a runaway.)

Therefore, this backlight control unit can be mounted on both sides by simply changing the voltage applied to the shutdown terminal C of the operational amplifier OP without changing the configuration of the backlight control circuit itself. It can be used for both the total station and the one-side mounted total station. Therefore, even when these two types of total stations are manufactured by the same maker, only one type of backlight control unit needs to be created, so the number of parts (units) does not increase, and management and maintenance costs are reduced. Can be reduced.

If a variable capacitor capable of varying the voltage between terminals is used as the reference voltage source E1, the operational amplifiers OP1 and OP1 are connected.
Since the reference voltage applied to the non-inverting input terminal of P2 can be varied, the brightness of the backlights L1 and L2 can be adjusted. Even in this case, the supply currents to the backlights L1 and L2 after adjustment are still kept constant.

[0038]

According to the backlight control circuit for a display of a surveying instrument of the present invention configured as described above, even if only a smaller number of backlights than the maximum connectable number are connected, the circuit configuration is completely eliminated. No need to change. Therefore, the backlight control circuit for the display of this surveying instrument can be shared by a plurality of types of surveying instruments each having a different number of indicators.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a backlight control circuit for a display of a surveying instrument according to an embodiment of the present invention.

FIG. 2 is a view of a total station mounted on both sides, on which the backlight control circuit of FIG. 1 is mounted, viewed from an opposite position.

FIG. 3 is a view of the total station shown in FIG. 2 viewed from a normal position.

FIG. 4 is a circuit diagram showing a case where the backlight control circuit 3 of FIG. 1 is mounted on a total station that is mounted on one side.

FIG. 5 is a circuit diagram showing a structure of a conventional backlight control circuit for a display of a surveying instrument mounted on both sides.

FIG. 6 is a circuit diagram showing a configuration of a conventional backlight control circuit for a display of a single-sided surveying instrument.

[Explanation of symbols]

 2 Main unit 4 First display 6 Second display C1, C2 Shutdown terminal E Reference voltage source L1, L2 Backlight OP1, OP2 Operational amplifier Q1, Q2 Transistor R1, R2 Resistance

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[Procedure amendment]

[Submission date] March 22, 1996

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

However, in the backlight control circuit for a plurality of backlights shown in FIG. 5, only one constant current circuit (opamp OP2, transistor Q2, resistor R2) should not be connected to the backlight L2. Then, the output side of this constant current circuit is in a no-load state. Therefore, the operational amplifier OP2 goes out of control, causing an excessive current to flow, resulting in an increase in current consumption.
Not only that, but in some cases, the constant current circuit itself and other circuits may be destroyed. Therefore, the conventional backlight control circuit unit for a plurality of backlights shown in FIG. 5 cannot be used as it is as a backlight control circuit for a single backlight.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

Therefore, when the conventional components of the backlight control circuit unit for a plurality of backlights shown in FIG. 5 are used as a backlight control circuit for a single backlight, as shown in FIG. Constituent circuit parts of the constant current circuit on the side not connected (operational amplifier OP2, transistor Q2, resistor R
2) had to be deleted from the circuit board. That is, conventionally, the backlight control circuit unit for a surveying instrument mounted on both sides shown in FIG. 5 and the backlight control circuit unit for a surveying instrument mounted on one side shown in FIG. 6 must be prepared as separate parts. There was no place for al. Therefore, the cost is high in manufacturing, management, and maintenance.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

This operational amplifier OP1 is an operational amplifier IC chip with a shutdown function, and is, for example, LIN.
The EAR TECHNOLOGY LTC1152 chip is used. That is, this operational amplifier OP1 has a shutdown terminal C1.
And is activated when an H level voltage is applied to the shutdown terminal C1, and enters a sleep state when an L level voltage is applied to the shutdown terminal C1. In this sleep state,
The current supplied to the operational amplifier OP1 itself is about 1 μA, and the output terminal side is in a high impedance state. When the shutdown terminal C1 becomes floating, this supply current pulls up the voltage of the shutdown terminal C1 to the H level state.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Delete

Claims (6)

[Claims] 1. A backlight control circuit for a display of a surveying instrument comprising a plurality of constant current circuits respectively provided for supplying a drive current to a plurality of backlights, wherein each of the constant current circuits is provided with the drive circuit. A resistor that converts a current into a voltage value and a voltage value and a reference voltage value that are converted by the resistor are input to each input terminal, and an output voltage corresponding to these voltage values is output from the output terminal and applied. An operational amplifier having a shutdown terminal that switches the impedance state of the output terminal to a high impedance state or a low impedance state according to the potential, and a transistor that controls the drive current according to the output voltage output from the output terminal of the operational amplifier. A backlight control circuit for a surveying instrument display. 2. The voltage value converted by the resistor is input to an inverting input terminal of the operational amplifier, and the reference voltage value is input to a non-inverting input terminal of the operational amplifier. The backlight control circuit for the display of the surveying instrument described in 1. 3. The transistor includes a base connected to an output terminal of the operational amplifier, an emitter grounded via the resistor, and a collector connected to a power supply for the drive current via the one backlight. 3. The backlight control circuit for a display of a surveying instrument according to claim 2, further comprising: an emitter voltage of which is input to an inverting input terminal of the operational amplifier. 4. The backlight control for a display of a surveying instrument according to claim 1, wherein the operational amplifier of each constant current circuit is input with the reference voltage output from a common reference voltage source. circuit. 5. The backlight control circuit for a display of a surveying instrument according to claim 1, wherein all the constant current circuits are mounted on a common substrate. 6. The display for a survey instrument according to claim 1, wherein the shutdown terminal of the operational amplifier sets the output terminal to a high impedance state when pulled down to a potential lower than a predetermined threshold value. Backlight control circuit.