JPH0375362B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a dimmer circuit for a display section of a vehicle-mounted device, and in particular allows brightness adjustment in multiple stages.

[Conventional technology]

Since the brightness inside the vehicle interior varies greatly depending on the environment outside the vehicle, good contrast cannot be obtained unless the brightness of the indicators and displays of the vehicle equipment is minutely changed. Also,
In some countries, this type of dimming control is mandatory.

FIG. 11 shows an example of a conventional dimmer circuit, which attempts to switch the brightness of the display of a car-mounted electronically tuned radio receiver between day and night. In the figure, 1 is an antenna, 2 is a high frequency stage (RF), 3 is a mixer (MIX), 4 is an intermediate frequency stage (IF), 5 is a detection circuit (DET), 6 is a low frequency amplifier (AFAMP),
7 is a speaker, 8 is a reception local (LO), 9 is a phase-locked loop (PLL), 10 is a low-pass filter (LPF), and 11 is a microcomputer (MPU) that also performs various operation processing and display processing of the radio receiver. ), 12 is a key matrix, 13 is a display, 14 is an illumination switch, 15
For example, is one of the lamps for character illumination, and +B is a battery.

The radio receiver in this example has MPU11 to PLL9.
Setting the division ratio of LO8, PLL9, LPF1
The frequency of LO8 is determined in a closed loop consisting of 0,
Also, the tuning frequency of RF2 is determined. MPU11
changes the frequency division ratio of the PLL 9 by inputting the key matrix 12, and also changes the display 1 at that time.
3. Change the display (frequency or channel display, etc.).

[Problem that the invention seeks to solve]

The dimmer circuit of the radio receiver described above regards the existing illumination switch 14 as part of the key matrix 12, and controls the MPU 11 to reduce the brightness of the display 13 when the switch is turned on (for example, by dynamic drive). (duty control). However, since the switch 14 turns on the side lamps in addition to the lamps 15 inside the vehicle, it is turned on not only at night but also in the evening. Therefore, if the brightness is also lowered to be suitable for nighttime, there is a drawback that the contrast of the display 13 decreases due to insufficient light in the evening. The difference in light intensity between the suburbs and the city also causes a decrease in contrast.

The present invention provides a variable resistor for dimer control separately from the illumination switch, thereby making it possible to control dimming in multiple stages.

[Means for solving problems]

The present invention is a variable resistor for controlling a dimmer, and an A/C converter that converts its output voltage into a digital value.
A D converter, a microcomputer that reads an output digital value of the converter, and a display section of an in-vehicle device whose display is controlled by the computer, and the computer adjusts the brightness of the display section based on the digital value. It is characterized by:

[Effect]

Equipped with a variable resistor for daymer control,
When the output voltage is converted into a digital value by an A/D converter, the computer that controls the display section of the vehicle equipment can read the digital value.
Therefore, by incorporating a program that adjusts the brightness of the display section based on the digital value, it becomes possible to adjust the brightness in multiple stages by manually operating the variable resistor.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention, which includes a manually operable variable resistor R1 and an A/D converter 20 that converts the output voltage V into a digital value and inputs it to the MPU 11. is the 11th
Different from the illustration. The variable resistor R1 is used to control the dimmer of individual in-vehicle equipment, and has a linear conversion characteristic as shown in FIG. The power divided by this variable resistor R1 is a constant voltage, and is supplied through, for example, an illumination switch. A/D
The converter 20 is connected to the MPU 11 as shown in FIG.
When it receives a start signal from
2 A/D conversion to ^N -bit digital value (data) with N resolution, and end signal END when conversion is completed.
is sent back to MPU11. MPU11 is this END
After receiving N bit data, the brightness of the display 13 is duty-controlled according to the value. FIG. 4 is a time chart of FIG. 3, in which the start signal is repeatedly generated in synchronization with the cycle in which the MPU 11 reads the state of the key matrix 12.

FIG. 5 shows a specific example in which the display 13 is a fluorescent display tube, where A is an anode of each segment, G is a grid, and H is a heater. The MPU 11 writes display data for each segment into the output register REG, and when the data is 1, the corresponding segment is turned on (0 is turned off). FET is a driver transistor that drives anode A. At this time, a dynamic drive method is adopted, and the brightness is adjusted by controlling the on-time ratio (duty ratio) of each segment to be lit. In other words, write 1 in half of the display period (for example, 10ms) of the same segment,
If 0 is written to the remaining half, the duty ratio will be 50%. 0 is written in the segments that are to be turned off throughout one cycle. The duty ratio in this case is 0
%. As the duty ratio increases, the brightness increases, and conversely, as the duty ratio decreases, the brightness also decreases. FIG. 6 shows that the duty ratio of the anode voltage of the segment to be lit is 50%, 75%, 25%, etc., corresponding to the N bit data taking the values N ₁ , N ₂ , N ₃ , ...
This shows how things change. This duty control is performed by a program of the MPU 11 (described later).

FIG. 7 is a flowchart of display control, using a synchronization flag and a display ON flag. The synchronization flag is used to specify the display cycle (for example, 10ms), and the display ON flag is set to 1 when displaying.
Make it. The display data output is the register shown in Figure 5.
This is the step of writing display data to REG. Timing signals ₁ to ₄ in FIG. 9 are sequentially applied to the 4.times.4 key matrix 12 (FIG. 1) to read key inputs. A/D input is variable resistor R
This is the digital value of the output voltage V of 1, which is the previous N-bit data. After this, there is a SW (switch) determination process, and further display data editing such as frequency and channel is performed. The last setting of t1 and t2 is the setting of the lighting time t1 and the lighting time t2 shown in FIG. 9, in other words, the setting of the duty ratio, and this is done based on the A/D input. An interval timer (not shown) built into the MPU 11 is used to count t1 and t2, and the interrupt processing is performed as shown in FIG. That is, MPU1
1, the interval timer is set to generate an interrupt by alternately counting t1 and t2, and the segment is turned on during time t1 and turned off during time t2. FIG. 9 shows a time chart showing the interrupt timing, display control, etc.

Thereafter, when an interrupt is generated by the interval timer while the MPU 11 is going through a main routine such as operation processing of on-vehicle equipment, the MPU 11 is forcibly moved to the subroutine shown in FIG. 8, and performs the above-mentioned processing.

The reason why t1 and t2 are counted by the interval timer in this way is as follows. That is, as is well known, if a count processing step is added to the main routine of the MPU 11 to count t1 and t2, the count step is based on the number of cycles of a certain routine in each operation process and display process of the in-vehicle equipment. You will be counting t1 and t2. Therefore, when the operating status of in-vehicle equipment changes,
This constant routine moves to another step, and the counting time increases accordingly. However, this count step judges this count time to be t1 or t2, so it is not normal.
t1 and t2 will no longer be the same, and as a result, an error will occur in the duty ratio.

In order to eliminate this error, the present invention uses a dedicated interval timer to accurately calculate t1 and
It is possible to count t2 and control the brightness of the display section with high precision.

The targets of the SW judgment process in Figure 7 are accessory switches (Acc), radio switches, auto search up (ASU), and power switches (power SW).
etc. are included. FIG. 10 is a flowchart of power SW processing. The aforementioned display ON flag is set only while the radio is ON, and necessary display data is displayed on the display 13 during that time.
On the other hand, when the display ON flag is reset when the radio is turned off, the interval timer operates constantly and no display is performed on the display 13 even if an interrupt is generated.

〔Effect of the invention〕

As described above, according to the present invention, by manually operating the variable resistor for dimmer control, the brightness of the in-vehicle device display section can be switched in multiple stages according to the surrounding brightness, and Good contrast can be maintained. Furthermore, in the present invention, in a microcomputer that also performs various operation processing and display processing of in-vehicle equipment, lighting and
We use a dedicated interval timer to count the time the lights go out, so we can accurately turn them on and off.
It also has the advantage of being able to count the light-off time and controlling the brightness of the display section with high precision.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Figure 2 is a characteristic diagram of the variable resistor for daymer control, Figure 3 is a detailed view of the main parts of Figure 1, Figure 4 is its time chart, Figure 5 is a circuit diagram showing a specific example of the display, and Figure 6 is a diagram showing a specific example of the display. The figure is an explanatory diagram of duty control, Figure 7 is a flowchart of display control, Figure 8 is a flowchart of duty control, Figure 9 is a time chart of display control, and Figure 10 is a power switch.
FIG. 11 is a block diagram showing an example of a conventional dimmer circuit. In the figure, R1 is a variable resistor, 11 is a microcomputer, 13 is a display, and 20 is an A/D converter.

Claims (1)

[Claims] 1. A variable resistor for daymer control of in-vehicle equipment, an A/D converter that converts its output voltage into a digital value, reads the output digital value of the converter, counts a predetermined time, and interrupts when the predetermined time elapses. A microcomputer is equipped with an interval timer that performs the interrupt processing, and a display section of the in-vehicle equipment whose display is controlled by the computer based on duty control. Each time a digital value occurs, a lighting time and a light-off time of the display section are set alternately in the interval timer, and the display section is turned on and off during the lighting time and light-off time. Daymer circuit for in-vehicle device display.