JPS62170817A - Dimming control device for electronic meter for vehicle - Google Patents

Abstract

PURPOSE:To keep a display luminance of an indicator constant even if battery voltage is varied, by varying both a digital value corresponding to an output of a dimming variable resistance, and a digital value corresponding to a battery voltage, by the battery voltage. CONSTITUTION:Between a light switch 4 and a microcomputer (muCOM)1a, an A/D converting circuit 1g for A/D-converting a divided voltage V2 by a voltage dividing resistance R3 and R4 of a voltage of a power source 5 is provided, and when the light switch 4 has been turned on, a power supply voltage data D4 which has been digitized by the A/D converting circuit 1g is inputted to the muCOM1a. The muCOM1a executes a control for adjusting the luminance of a fluorescent display tube by a ratio D1/D4(V1/V2) of a dimming data D1 inputted from an A/D converting circuit 1c and the power supply voltage data D4 inputted from the A/D converting circuit 1g.

Description

[Detailed Description of the Invention] [Summary of the Invention] The duty ratio of a rectangular wave is determined by the ratio of the digital value obtained by a variable resistor for dimming and the digital value obtained by a bathotery voltage, and the duty ratio of the rectangular wave is determined by the duty ratio of the rectangular wave. By dimming the display on the display, changes in the brightness of the display due to battery voltage fluctuations are prevented.

[Industrial application field]

The present invention relates to a light control device for a vehicle electronic meter.

[Conventional technology]

Many of the recent vehicle meters such as speed needles, rotation needles, and various gauges are computerized, and electronic displays that provide digital display using numerical displays, bar displays, etc. are used.

Such electronic displays include liquid crystal displays, LED displays, fluorescent display tubes, etc., and use light for display.

In such a display, if the brightness is increased so as to provide sufficient visibility during the day, the display becomes too bright at night, making it easy for the eyes to get tired. Therefore, a light control device is provided so that display brightness can be adjusted at night.

Conventionally, there has been a device of this type, as shown in FIG. 4, which is applied to a speed hand. In the figure, 1 is an electronic speed hand, 2 is a speed sensor, 3 is a variable resistor for dimming, 4 is a light switch, and 5 is a power source consisting of a bath battery.

The speed sensor 2 is composed of a photocoupler, a pickup coil, etc., which detects the rotation of a part linked to the wheels of the vehicle, and generates a speed signal SPo consisting of a pulse train whose frequency changes depending on the running speed of the vehicle.The electronic speedometer 1 to be applied. The dimming variable resistor 3 applies a voltage Vo to the electronic speedometer 1 according to the position of its movable contact when the night light switch 4 is turned on.

The electronic speedometer 1 receives a speed signal SPo from the speed sensor 2, and has a microcomputer (μCOM) la that measures and calculates vehicle speed based on the speed signal SPo and outputs speed display data SP+. The μC0M1a also detects turning on of the light switch 4 connected via the interface 1b. At this time, the voltage Vo generated by the dimming variable resistor 3 is divided by the resistors R1 and R2, and the voltage (1) is converted into a digital signal D1 by the A-D conversion circuit IC. The digital signal D+
is accepted as dimming data in μC0M1a. μ
C0M1a generates duty ratio determining data D2 based on the dimming data D], and applies this to the variable duty rectangular wave generation circuit 1d.

The variable duty rectangular wave generation circuit 1d generates a rectangular wave D3 having a duty ratio corresponding to the duty ratio determination data D2, and applies this to the display driver 1e. The display driver 1e receives the speed display data SP+ from μC0M1a, and drives the numerical display 1f based on the speed display data SP1 to digitally display the speed. At this time, the display driver 1e also controls the lighting time of the numeric display 1f per unit time based on the duty ratio of the rectangular wave applied from the variable duty rectangular wave generating circuit 1d.

Therefore, the display brightness of the numeric display 1f is adjusted by the dimming variable resistor 3.
The light can be varied and dimming can be performed by changing the duty ratio.

In the above configuration, the operation of speed display will be explained below.

When the vehicle runs, the speed sensor 2 generates a pulse train of 20 pulses or 25 pulses per revolution as a speed signal SPo, which is passed through a waveform shaping circuit (not shown) to μC0M1.
Apply to a. μCOMIa counts the pulse train of the speed signal SPo, calculates it, and stores it. This speed data is then converted into speed display data SP1 consisting of 20-bit serial data and output to the display driver 1e.

The display driver 1e is configured as shown in FIG. 5 in more detail. Input terminals 11 to I3 have μC0M1a
A clock signal CK as a shift pulse and a latch signal LH are respectively inputted as speed display data SP+ which is a 120-bit serial digital signal, and input terminal 4 receives a rectangular waveform whose duty ratio during dimming can be changed from a variable duty rectangular wave generation circuit 1d. A dimming signal D3 consisting of waves is manually generated. Output terminals a2 to fo are connected to corresponding segments of a "day"-shaped numeric display If (FIG. 4) shown in FIG. 6. Note that since the segment fo in the hundredth place is unused, there is no output fo.

Now, the clock signal CK and the speed display data SPi, which is 20-bit serial data, are sent from μC0M1a to the 20-bit serial shift register le2 via the input terminal I3.
When the speed display data SP1 is inputted into the 20-bit serial shift register 1e2, it is shifted by the clock signal CK and set in the 20-bit serial shift register 1e2. Next, the launch signal LH from μC0M1a is sent to the control circuit 1e+ via the input terminal ■2.
20-bit serial shift register 1
'82 contents are 20 bits display buffer register le3
will be forwarded to. 20-bit display buffer register le3
The contents of each bit are inputted to each segment of the numeric display If (FIG. 4) via a NAND circuit and an inverter. If the numerical display 1f (Fig. 4) consists of a fluorescent display tube, a 20-bit display buffer register le
The segment corresponding to the "H" focus of 3 is lit.

A rectangular wave as a dimming signal is inputted to one input terminal of the NAND circuit from the variable duty rectangular wave generating circuit 1d (Fig. 4) via the input terminal I, and the rectangular wave is "H". The display lights up during the period, and goes off while it is "L". For example, as shown in FIG. 7(a), a rectangular wave D3 which is a dimming signal
changes, the output corresponding to a particular segment of the 20-bit display buffer register, e.g.
When the signal is "H" as shown in FIG.
), the lighting time is controlled and the display dimming is performed.

Next, the display dimming operation will be explained below based on FIG. 4.

In the case of a numeric display 1f made of a fluorescent display tube, the relationship between the input voltage 1 of the A-D converter circuit IC and the display brightness of the fluorescent display tube is shown in FIG. 8, and the light switch 4 When turned on, the light from the fluorescent display tube is linearly dimmed by varying the dimming variable resistor 3.

The voltage V1 that changes due to the variable resistance 3 is A-D
The conversion circuit IC converts the light into dimming data D1 consisting of an 8-bit serial digital signal. (2) The relationship between 1 and Dl is as shown in FIG.

The output format of the dimming data D+ from the A-D conversion circuit IC is a total of 10 bits, including start and end bits, as shown in Figure 10 (synchronized with the clock signal CK shown in al, the top of Figure 10). output in the form

μC0M1a processes the dimming data D+ inputted from the A-D conversion circuit IC according to the flowchart described later based on a predetermined program, and processes the duty ratio determination data D
Convert to 2. The variable duty rectangular wave generation circuit 1d to which this duty ratio determining data D2 is input is operated by the data D2.
A rectangular wave with a duty ratio corresponding to the output voltage is output as the dimming signal D3.

In more detail, the variable duty square wave generation circuit 1d is as follows:
It is constructed as shown in FIG.

Input terminals 11 to I3 receive clock pulses CK1. from μC0M1a. CK2 and duty ratio determining data D2 are respectively input, and dimming data D3 consisting of a rectangular wave is output from the output terminal O.

Now, when the duty ratio determining data D2 consisting of a clock pulse CKl and an 8-bit serial signal is input from μC0M1a to the 8-bit shift register di through input terminals 11 and 13, it is shifted by the clock pulse CK 1 and the duty ratio is determined. Data D2 is set in 8-bit shift register d1. Assuming that the data Ilh set in the 8-bit shift register d1 is a decimal number "120", this data D2 is first compared with the content CO of the comparison 8-bit counter d2 in the reset state in the magnitude comparator ld3. At this time, since D2≧CO, the rectangular wave D3 at the output terminal O of the magnitude comparator ld3 becomes H''.

The comparison 8-bit counter Id2 sequentially counts and amplifies the clock pulse CK2 shown in FIG. becomes the decimal number 1121” as shown in Figure 12 (011), then D
+<Co, and the rectangular wave D3 at the output terminal 0 of the magnitude comparator 1d3 is inverted to "L" as shown in FIG. 12(a).

As the 8-bit counter ILa continues to count up, the 8-bit counter ld2 rolls over at the n=256th clock pulse CK2, and its content CO becomes 10.
The base number “255” becomes “000”. At this time, the process returns to the start state, and the rectangular wave D3 at the output terminal 0 becomes "H".

From the above, the duty ratio determination data D2 is set to the decimal number “1”.
20"=hexadecimal number "78", the duty ratio of the rectangular wave D3 is 121/256, and the duty ratio is generally determined as (D2+1)/256.

Next, the dimming process performed by μC0M1a according to a predetermined program will be described with reference to the flowchart shown in FIG.

For example, the μC0M1a starts executing the flowchart in response to the key-on of the vehicle, and in the first step S1 determines whether the light switch 4 is turned on by monitoring the voltage applied via the interface 1b. .

When the light switch 4 is off, the determination in step S1 is NO, and the process proceeds to step S2, where the duty ratio determination data D2 is converted to decimal number "255" = hexadecimal number F.
F''. Then, the set data D2 is output in the next step S3. By this,
The duty ratio of the rectangular wave generated by the variable duty rectangular wave generating circuit 1d is 256/256=1, and the fluorescent display tube is lit at 100% brightness.

When the light switch 4 is on, the determination in step S1 is YES, and the process advances to step S4, where the dimming data D1 is taken in. In the subsequent step S5, it is determined whether or not the captured data D1 satisfies V1≦o, 08V and D1≦decimal number “8”. If the determination is YES, the process advances to step s6, where the duty ratio determination data D2 is set to decimal number "7", and the cent D2 is outputted in step S3. As a result, the duty ratio of the rectangular wave generated by the variable duty rectangular wave generating circuit 1d becomes 8/256, and the display on the fluorescent display tube is dimmed. The display at this time has the minimum brightness.

When the determination in step S5 is NO, that is, V+
=0.08 to 2.55 VteD2> When the decimal number is "8", the process proceeds to step S7, and the process is performed in response to the dimming data D1 taken in step s4 so as to have the dimming characteristics as shown in FIG. The duty ratio determining data D2 is sent, and the sent data D2 is output in step S3. As a result, the fluorescent display tube becomes (D2
It is turned on with a rectangular wave with a duty ratio of +1)/256, and is dimmed by adjusting the dimming variable resistor 3.

After executing step S3, the process returns to step S1 and the above-described operations are repeated.

[Problem that the invention seeks to solve]

In the above-mentioned conventional light control device, when the vehicle bathymetry voltage changes while the night light switch 4 is turned on, the input voltage V+ to the A-D converter circuit 1c changes, and the output light control data Dl changes. will also start to fluctuate.

For example, when the battery voltage changes from 13V to 12V, the fluorescent display display will dim by about 10%. At this time, the power supply voltage for the fluorescent display tube also decreases slightly, so
This effect also adds to the dimming.

For this reason, the display on the fluorescent display tube becomes brighter or darker depending on the fluctuation of the pathometry voltage, and the display may appear flickering at night because the surroundings are dark.

Note that since the variable resistor 3 is directly connected to the battery 5, there is a risk that the circuit within the electronic speedometer 1 will be damaged if a surge voltage occurs. Therefore, a capacitor (not shown) is installed in the electronic speedometer 1 to absorb surges to protect the circuit, but even when such surges occur, voltage fluctuations occur and display brightness changes. Vary.

[Means for solving problems]

The present invention provides a dimming device for a vehicle electronic meter in which the brightness of a display in a dimming state does not change even if the voltage of the vehicle battery changes, and flickering due to brightness and darkness of the display does not occur. For this purpose, a device made according to the present invention comprises: a dimming variable resistor to which battery voltage is applied; a first A-D converter circuit that converts the output of the variable resistor into a digital value; A rectangular wave generating means for generating a rectangular wave with a duty ratio corresponding to a digital value of an output of an A-D converter circuit, and adjusting the display of a display device according to the duty ratio of the rectangular wave. In the light control device, a second A-D converter circuit that converts a battery voltage into a digital value, and the first and second A-D converter circuits that convert battery voltage into a digital value;
It is characterized by comprising means for determining a duty ratio of the rectangular wave generated by the rectangular wave generating means based on a ratio of digital values of the D conversion circuit.

[For production]

The digital value corresponding to the output of the dimming variable resistor and the digital value corresponding to the battery voltage both change depending on the battery voltage, so the ratio of these values is always constant, and the duty ratio is determined by the ratio. The display brightness of the dimmed display does not change due to variations in battery voltage.

〔Example〕

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

FIG. 1 shows an embodiment of a dimmer device for a vehicle electronic meter according to the present invention, in which parts equivalent to those of the conventional device described above with reference to FIG. 4 are given the same reference numerals.

In FIG. 1, an A-D converter circuit 1g is provided between the light switch 4 and μC0M1a to A-D convert the voltage divided by the voltage dividing resistors R3 and R2 of the power supply 5. 4 is turned on, the power supply voltage data D4 digitized by the A-D converter circuit 4g is μ.
It is designed to be input to C0M1a.

μC0M1a is the ratio Dr/D4 (=V+/V
2), perform control to adjust the brightness of the fluorescent display tube, for example, set V2 = 2.55V, and set Vl to 2.55V.
Control is preset by a program described later so that the brightness changes as shown in FIG. 2 when the brightness is changed to OV.

Setting conditions for dimming characteristics depend on the user's preferences, but in general, the brightness of the meter illumination light source is determined by considering voltage characteristics, balance with meter brightness, minimum brightness, brightness change rate within the dimming operation range, etc. It will be done.

The dimming process performed by μC0M1a according to a predetermined program will be explained with reference to the flowchart of FIG.

μC0M1a starts its work in response to, for example, turning on the key of the vehicle, and in the first step S1 determines whether the light switch 4 is turned on or not by monitoring the output of the interface 1b.

Light switch 4 is off and the determination in step 311 is NO.
When this happens, the process proceeds to step S12, where the duty ratio determination data D2 is set to a decimal number "255", and the set data D2 is output in the subsequent step S13. By this, variable duty square wave generation circuit 1
d outputs a rectangular wave with a duty ratio of 256/256=1, and lights up the fluorescent display tube at 100% brightness.

Light switch 4 is on and step Sll is determined as YE.
When S, the process advances to step 314, where data D+ is obtained from the A-0 conversion circuit 1c and Ig.

D4 is fetched, and in the subsequent step S15, the ratio R=D1/D4 of the fetched data Ilh and D2 is calculated.

The ratio R calculated in step 315 is then calculated in step 316.
It is determined whether R≧1 or not, and when R≧1 and the determination is YES, the data D2 is set to l in step S12.
The set data D2 is set to O base number “255”.
is output in the next step 513. The brightness at this time is 100%, the same as when light switch 4 is off.
It is.

If the determination in step S16 is No, step S17
Then, it is determined whether R≧0.9.

When the determination in step S17 is YES, the process proceeds to step 318, where D2 is set using a predetermined calculation formula based on the dimming characteristic curve in FIG. 2, and the set data D2 is output in step 313.

If the determination in step S17 is No, step S19
Then, it is determined whether R≧0.7.

When the determination in step 319 is YES, the process proceeds to step 320, and a predetermined calculation formula based on the dimming characteristic curve of FIG. 2 is output in step S13.

If the determination of Stain 7”S19 is No, step 32
1, where it is determined whether R≧0.5. When the determination in step S21 is YES, the process proceeds to step S22, where D2 is set using a predetermined calculation formula based on the dimming characteristic curve of FIG. 2, and the set data D2 is outputted in step S13.

When the determination in step S21 is No, the process proceeds to step 323, where the data is converted to the decimal number "7".
, and outputs it in step S13.

After outputting the data D2 in step 313, the process returns to step S11 and the above steps are repeatedly executed.

It should be noted that the calculation formulas in steps Sl B , 320 and S22 are determined in step S20 (0,7≦
D≦0.9) will be described below as an example.

Since the duty ratio determination data D2 that determines the duty ratio of the square wave consists of 8 bits, the duty ratio is 256.
divided into. In Figure 2, the width of the horizontal axis is 0.9-0
．． 7 = 0.2, and the width of the vertical axis is 128-26 = 1
02, the duty ratio for any R between 0.7 and 0.9 is as follows. Since the data D2 output is set by -1 due to the variable duty rectangular wave generation circuit 1d, the actual set value of D2 is as follows.

Now, if R = 0.7, then it becomes ``19'' in hexadecimal. Other calculation formulas are obtained in the same manner as described above.

By the way, if the key switch is turned on at any point in time,
Light switch 4 is on, v2 is 2V.

Assuming that Vl is 1.6v, the brightness is as follows.

R= Vl / V2 = 0.8 Duty ratio (76+1)/25640.3 Brightness approximately 30
% In this condition, the engine is started and the voltage is V -1
Assuming that the voltage increases to 4V, Vl and V2 change according to the following relational expressions.

V+ = AV 吋 V2 = BV Note that A is resistance R + g R2, variable resistor 3,
B is determined by resistors R3 and R4, respectively.

Therefore, the ratio R = V 1 / V e = A / B, and even if the liver changes, as long as A does not change by adjusting the variable resistor 3, Vl / V2 will remain constant, and the brightness will fluctuate due to voltage fluctuations. That will no longer be the case.

〔effect〕

As explained above, according to the present invention, the display brightness of the display does not change even if the battery voltage fluctuates, which eliminates flickering of the display and eliminates the troublesome readjustment of dimming every time the brightness changes. Effects such as not being necessary can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the device according to the present invention, FIG. 2 is a graph showing the dimming characteristics of the device of FIG. 1,
FIG. 3 is a flowchart of the work performed by μCOM in FIG. 1, and FIG. 4 is a block diagram showing an example of a conventional device.
5 is a block diagram showing a specific circuit example of the display driver in FIG. 4, FIG. 6 is a diagram showing the segment arrangement of the numeric display in FIG. 4, and FIG. 7 is a block diagram of the circuit in FIG. 5. FIG. 8 is a graph showing the dimming characteristics of the device in FIG. 4. FIG. 9 is a graph showing the input/output characteristics of the A-D converter circuit in FIG. Figure 10 is A in Figure 4.
-A timing chart diagram showing the output formant of the D conversion circuit, Figure 11 is a block diagram showing a specific circuit example of the variable duty square wave generation circuit in Figure 4, and Figure 12 is the operation of the circuit in Figure 11. FIG. 13 is a flowchart of the work executed by μCOM in FIG. 4. 1...Electronic speed hand, 1a...Microcomputer (μCOM), IC...A-D conversion circuit, 1d...
- Variable duty rectangular wave generation circuit, 1e...Display driver, 1f...Numeric display, 1g...A-D conversion circuit, 3...Variable resistor for dimming, 5...Battery.

Claims (1)

[Scope of Claims] A dimming variable resistor to which battery voltage is applied, a first A-D converter circuit that converts the output of the variable resistor into a digital value, and a digital value of the output of the A-D converter circuit. and a rectangular wave generating means for generating a rectangular wave with a duty ratio according to the duty ratio of the rectangular wave, the dimming control device for a vehicle electronic meter dimming the display of a display according to the duty ratio of the rectangular wave, a second A-D converter circuit for converting into digital values; and means for determining a duty ratio of a rectangular wave generated by the rectangular wave generating means based on a ratio of digital values of the first and second A-D converter circuits. What is claimed is: 1. A dimming control device for a vehicle electronic meter.