FR2752465A1 - METHOD FOR ADJUSTING THE BRIGHTNESS OF A VISUALIZATION DEVICE - Google Patents

Abstract

The duty cycle of a pulse width modulated control signal is determined and a brightness control signal is established as a function of the duty cycle, this signal serving to control the brightness of the display device (4) for example. a dashboard (8) of a motor vehicle. According to the invention, a rising or falling edge of the control signal is detected, which triggers a counter (9) at an initial instant, the counter overflows are counted, a falling or rising edge is detected so that at an instant intermediate, the state of the counter and the overflows are stored in a memory (2) as an intermediate state, a rising or falling edge is detected so that at a final instant, the state of the counter and the overflows are stored in memory as the final state and, from the ratio of the final state to the intermediate state, a duty cycle proportional to this ratio is determined. This process saves computation time as part of the calculator (1).

Description

The present invention relates to a method for adjusting the brightness of a

  display device, wherein the duty cycle of a pulse width modulated control signal is determined and a brightness control signal is set in accordance with the duty cycle, which signal is used to control the brightness of the

viewing device.

  The brightness of a display device is for example adjusted by means of a light dimming potentiometer which, depending on its setting, provides a rectangular signal having correspondingly high phases of a corresponding length for a prefixable period of time. A long high phase corresponds to a luminous display device and a brief high phase to a dark device. The duty cycle between the high phase and the period of the potentiometer signal constitutes the input value on the basis of which is read, from a graph, the value of a characteristic which fixes in advance the duty cycle. a pulse width modulated signal by which the brightness of the display device

is set.

  In the state of the art, the duty cycle of the potentiometer signal is determined for each period, that is to say for example between two falling edges of the rectangular signal, by means of an analysis of the value of the signal. potentiometer, at a high frequency, and a calculation of the duty cycle from this value. The known method, however, is a large consumer of calculation, since it is at a high frequency that the potentiometer signal is

  analyzed and evaluated for each period.

  The object of the invention is to provide a simple method for determining the brightness of a display device, which requires only a little bit of the computing unit. According to the invention, this object is achieved in a method of the generic type defined in the preamble by the fact that a rising or falling edge of the control signal is detected and, as a function of this detection, a counter is triggered. at an initial time, that the overflows of the counter are counted, that a flank is descending, the amount of the control signal is detected and, depending on this detection, at an intermediate time, the state of the counter and the overflows of the counter are stored in memory as an intermediate state, then a respectively rising or falling edge of the control signal is detected and, depending on this detection, at a final time, the counter state and the overflows of the are stored in memory as a final state and that from the ratio of the final state to the intermediate state, a cyclic ratio proportional to the ratio of the final state to the intermediate state is determined. It is particularly advantageous not to analyze the potentiometer signal, but, each time by means of the rising edge and the falling edge, to determine the duty cycle. An advantage also lies in not evaluating the potentiometer signal for each period, but at predetermined time intervals, which reduces the load on

the unit of calculation.

  The invention may also include one or more of the following features: - in the case of an overflow occurring almost simultaneously with a rising or falling edge, the state of the counter is examined and the overflow is recognized only

  when at that moment the meter status is

  below a state that can be prefixed and the edge is recognized only when at this moment, the state of the counter is above a state that can be prefixed, - by means of the control signal of brightness, a luminosity value is read in a graph and the dependence between the brightness value and the brightness control signal is set by means of two straight lines which interconnect three pairs of prefixed values, - for a lower domain of values and for a higher range of values of the brightness control signal, a constant brightness value is prefixed for each, - for the lines, only a prefixed number of slopes are used, - the two lines, having slopes prefixed starting from the central pair of values, are oriented respectively towards the third and the first pair of values, - it is first of all the range of values in which the duty cycle of the signal of which command is determined, then a pair of values, preferably the nearest pair of values, is selected, the difference between the duty cycle of the control signal and the value x of the chosen pair of values is determined, and, the value y of the chosen pair of values, the slope of the straight line of the domain in which the duty cycle falls is added or subtracted as often as it is prefixed by the value of the difference and thus a fixed value y is obtained

  the brightness of the display device.

  The invention is described below with reference to the figures. FIG. 1 shows a device for implementing the method, in FIG. 2 a potentiometer signal, in FIG. 3 a time flow diagram, in FIG. 4 a first example of measurement. in FIG. 5, a second measurement example, in FIG. 6, a third measurement example, in FIG. 7, a characteristic curve and, in FIG. 8, a graph provided for the brightness adjustment. FIG. 1 schematically represents a dashboard 8 of a motor vehicle which comprises a display device 4 and a light dimming potentiometer 3, the light dimming potentiometer 3 being connected to a calculation unit 1 by a signal line 6 and the display device 4 being connected by a control line 5 to the calculation unit 1 which, in addition, has access to a memory 2 via a data line 7 and communicates with a counter 9. Depending on its setting , the light dimming potentiometer 3 delivers to the calculation unit 1 a potentiometer signal having a corresponding duty cycle. FIG. 2 shows the potentiometer signal that is transmitted from the light dimming potentiometer 3 to the calculation unit 1 by the signal line 6 as a control signal. At the instant Ti, the potentiometer signal rises from the value Low to the value High and falls at the time T2 from the value High to the value Low, then to go up to the value High at the instant T3. The DP dimmer period results from

  the time interval between the instant T3 and the instant Tl.

  The duty cycle TA of the potentiometer signal is calculated from the time DH, during which the potentiometer signal is switched to High, relative to the

  DP dimmer period. TA = (T2 - T1) / (T3 -

  T1). Preferably, the duty cycle TA is multiplied

  by the value 256 and so reported to a byte.

  Figure 3 shows the schematic flow diagram of the method according to the invention. At the program point 10, the signal line 6 is examined by the calculation unit 1 to establish whether the potentiometer signal has a rising edge, i.e. a passage from Low to High, which produces a signal interrupted by flank. The calculation unit 1 is designed so that a rising or falling edge of the potentiometer signal produces an interrupt signal per side each time. If this is the case, at the program point 11, the calculation unit 1 then triggers at the instant Tl the counter 9 which counts from the value 0 to the value 256 in 3.072 ms and which, for the value 256, transmits an overflow interruption signal to the calculation unit 1, then starts counting again from 0. The calculation unit 1 continuously counts the interruption signals of

  overflow which are delivered by the counter 9.

  Then, at the program point 12, the calculation unit 1 notes, under the effect of an interruption signal per side, that the potentiometer signal has a falling edge, that is to say performs a passage from top to bottom. If this is the case, at the instant of the edge interruption signal, the state of the counter 9 is then maintained. Next, the state of the counter 9 and the number previously recorded of the overflow interruption signals of the counter 9 are recorded in FIG.

  memory 2 as intermediate time T2.

  Then, at program point 13, the computing unit 1 examines whether the signal line 6 is transmitting a rising edge again. If this is the case, an edge interruption signal is then produced in the calculation unit 1 and the state of the counter 9 at the time of the edge interruption and the number of overflow interrupts detected since the trigger time are stored in memory 2 as the final time T3. Then, at program point 14, the evaluation of the potentiometer signal is carried out by the calculation unit 1, the DP dimmer period being calculated as follows: DP = T3 - T1. The DH time during which the signal potentiometer has a high state is determined according to the following formula: TH = T2 - T1. The standard duty cycle DT of the potentiometer signal is calculated as follows: DT = (T2 - T1) * 256

/ (T3 - T1).

  Then, at program point 15, the standard duty cycle DT of the potentiometer signal is used by calculation unit 1 to read, from a graph, the value y of a light dimmer characteristic which represents the cyclic ratio, in particular the high duration, of the pulse width modulated signal by means of which the calculation unit 1 controls the brightness of the display device 4. The calculation unit 1 reads the brightness value from the graph and controls the display device 4 by means of a suitable pulse width modulated signal. We then loop back

on program point 10.

  FIG. 4 diagrammatically represents the variation over time of a signal according to a first measurement example, FIG. 4a showing the variation of the pulse width modulated potentiometer signal, while the arrows of FIG. 4b represent the signals. overflow interruption of the counter 9, the arrows of FIG. 4c of the edge interrupt signals serving as initial instant T1 for a rising edge, of intermediate instant T2 for a falling edge and of final instant T3 for a rising edge of the signal

  potentiometer modulated in pulse width.

  The states of the counter 9 are represented in FIG. 4b at the top without the number of overflow interrupts and they are read by the calculation unit 1 at the instants T1, T2 and T3 and deposited in the memory 2, then, at from there, taking into account the number of overflow interruption signals, which are shown in FIG. 4b at the bottom, and the timing of the counter 9, the period of the light dimmer DP is calculated in accordance with the values of the Figure 4c in which the states of the counter are represented with the overflow interrupts as hexadecimal numbers: DP = (0535H-0040H) x 12ps = 1269x12ps = 15.3ms. The rhythm is 12 ps. The high phase TH is calculated as follows: TH = (0280H-0040H) × 12 us = 576 × 12 us = 6.9 ms. The standard cyclical report DT is

  then has the form: DT = TH * 256 / DP.

  FIG. 5 represents a second measurement example, FIG. 5a showing the pulse width modulated potentiometer signal, FIG. 5b overflow interruption signals and counter states 9 and FIG. 5c counter states. for a rising edge (edge interrupt) at time T1, for a falling edge (edge interruption) at time T2 and for a rising edge (interruption by

flank) at time T3.

  The period of dimmer DP is calculated as follows: DP = (T3 Tl) x ZT = (04COH - 1OOlOH) x ZT = 1200 x 12 ms = 14.4 ms, the rate ZT of counter 9 being equal to 12 gs . The high phase DH of the potentiometer signal is calculated as follows: DH = (T2 - T1) x ZT

  = (0315H - 0010H) = 773 x 12 us = 9.3 ms.

  Since the falling edge (flank interrupt) at time T2 occurs almost simultaneously with the third overflow (overflow interrupt) and the flank interrupt and the overflow interrupt are written to the same address in the memory 2, the calculation unit 1 can not

  not to distinguish which interruption took place first.

  This is why it is necessary to carry out a plausibility check with which it can be ascertained if it is first the overflow (overflow interruption) of the counter 9 or the falling edge (interruption by sidewall). of the signal

potentiometer that has occurred.

  This is achieved by the fact that, in the decision as to whether it is first an overflow interruption or a flank break which has taken place, account is taken of the status of the meter. such that the overflow interrupt signal is assumed to be the first when the counter state is less than a prefixable count value, in particular 127, and is assumed to be first the flank break that took place

  when the state of the counter 9 is greater than 127.

  FIG. 6 represents a third example of measurement, FIG. 6a showing the potentiometer signal, FIG. 6b the moments of the overflows (overflow interrupts) and the states of the counter 9 and FIG. 6c the rising and falling edges instants (interrupts per side) of the potentiometer signal with the state of the counter, taking into account the overflows of the counter 9 at the times T1, T2, T3, and the number of overflows of the counter 9. The period of the DP light variator is calculated as follows : DP = (T3 - T1) x ZT = (0510H - OOEOH) x ZT = 1072 x 12 ps = 12.9 ms. The high phase DH of the potentiometer signal is

  calculates as follows: DH = (T2 - T1) x ZT = (02C5H -

OOEOH) = 485 × 12 us = 5.8 ms.

  This results in the following DT duty cycle: DT =

(DH * 256) / DP.

  In this exemplary embodiment, the falling edge (edge interruption) of the potentiometer signal occurs at time T2 and an overflow (overflow interruption) of counter 9 almost simultaneously, so it is necessary to check whether first is the overflow of counter 9 or the falling edge that has occurred. To do this, as already described, it is assumed that it is first the overflow interruption that occurred when the state of the counter 9 is smaller than 127 that can be prefixed. The flank interrupt is recognized as being the first in time when the state of the counter 9 is greater than or equal to 127. If, during the determination of the duty cycle, there is a phenomenon which calls upon the unit of calculation 1, so that the monitoring of overflows (overflow interruptions) can no longer be performed, the determination of the duty cycle is interrupted, the values already determined are rejected and the determination of the duty cycle is again

  triggered by calculation unit 1.

  The determined duty cycle is used to read a brightness value, used to control the display device 4, from a light dimmer characteristic deposited in the memory 2. In this exemplary embodiment, the duty cycle is used in as a value x from which is read, on the light dimmer characteristic which is represented in FIG. 7, a value y which constitutes a brightness value with which the display device 4 is controlled by the calculation unit 1. Preferably, the display device 4 is controlled by means of a pulse width modulated signal having a duty cycle that can be prefixed, the brightness of the display device 4 being proportional to the duty cycle, which is itself proportional to the value y of the

  dimmer characteristic (Figure 7).

  A particularly effective form of the light dimmer characteristic is to divide the characteristic into four value domains, as shown in FIG. 7, the first domain of values determining a minimum brightness which sets the value y1 = 21 for a value range x from x = 0 to x = 55. In this way, for values x which correspond to a duty cycle of the potentiometer signal which is less than 55, it is always the value y 21 which is transmitted to the device of

visualization 4.

  The second domain of values is fixed by means of the two pairs of values (x1 = 55, y1 = 21) and (x2 = 148,

  y2 = 84) which are connected to each other by a straight line.

  In the second value domain, according to the line that passes between the first and second pairs of values, a corresponding value y is read from a value x by means of which the

  viewing device 4 is controlled.

  The value y extracted from the graph is multiplied by the time unit by 12 ps and thus the duty cycle of the pulse width modulated signal is obtained.

  which the display device 4 is controlled.

  For a period of the pulse width modulated signal of 3.072 ms, a time for the high phase of 50 * 12 us occurs for a value y of 50, which leads to a duty ratio of the control of the device of

  visualization which is (50 * 12 ps) / 3.072 ms.

  The third domain of values extends from the second pair of values (x2 = 148, y2 = 84) to the third pair of values (x3 = 202, y3 = 255). The second and third pairs of values are also connected by a straight line. In the second value domain, according to the connecting line between the second and the third pair of values, the display device 4 reads, from the value x, a corresponding value y in accordance with which the brightness of the display device 4

is prefixed.

  The fourth domain of values is valid for values x which are greater than 202 and which is associated with a constant brightness value which is y = 255. At each duty cycle of the potentiometer signal which corresponds to a value x greater than 202, it is associated with a value y = 255 by means of which the display device 4 is controlled. The brightness of the display device 4 is determined according to the following method: the first, the second and the third pairs of values are stored in the memory 2. Similarly, the slope between the first and the second pair of values and that between the second and third pairs of values are written in the memory 2. If the evaluation of the duty cycle of the potentiometer signal then indicates that it has a value less than 55, the display device 4 is then always controlled with a value y Similarly, for a duty cycle with a value greater than 202, the

  visualization 4 is controlled with a value y of 255.

  If the evaluation of the duty cycle of the potentiometer signal provides a value x of 120, first the difference between the value x of the second pair of values, which represents a fulcrum, and the value x determined which is worth 120. In this case, the

  difference is equal to the value 28.

  Then, the slope for a value x of the graph of the first line sl, which is written in the memory 2 and which is 0.68 in the present embodiment, is subtracted 28 times from the value y2 of the second pair of values. and the brightness value with which the display device 4 is controlled by the control apparatus is thus determined. This is a

  chain addition that is performed.

  Preferably, the point of support is the pair of values which is located closest to the value

x of the potentiometer signal.

  If the evaluation of the duty cycle of the potentiometer signal provides a value x which lies between the value x of the second pair of values and that of the third pair, then the difference between the determined value x and the second value x which is determined. The difference value represents the number that determines how many times the second value s2 is added to the second value y, which is written in the memory 2 and in this embodiment shows the slope 3.16, and the sum final additions chain is the corresponding brightness value with which the display device 4 is controlled. If the difference value is 10, the slope of the second straight line is then added 10 times to the second value y. In this case too, it is

  the principle of chain addition that is used.

  The principle of chain addition can also be used in processes in which the duty cycle is determined in another way or is directly prefixed. The advantage of the economy of calculation is obtained for each process for which, with the aid of an input value (value x), an output value (value y) must be determined or read by means of a characteristic that has a constant slope from

a pair of values.

  It is particularly advantageous, in calculating the luminosities, to always start from the second pair of values, that is to say the central pair (x2, y2), since this way of proceeding allows a simple calculation of the brightness which offers the further advantage that, for the first straight line sl and the second line s2, it is not slopes whose finesse of the staging is arbitrary which must be written in the memory 2, but it is sufficient, as this is represented in FIG. 8 by a prefixed number of slopes m by means of which the slopes m are approximated between the pairs of values, which reduces the memory capacity

necessary for slopes.

  Because of the limited number, represented in FIG. 8, of prefixed slopes for the first and the second straight lines s1, s2 and because of the procedure of always starting the first or second line of the second pair of values x2 , y2, it is not always possible for the first pair of values x1, y1 and the third pair of values x3, y3 to be controlled in a precise manner. It may therefore happen that, in the region of the first pair of values x1, y1 and in the region of the third pair of values x3, y3, there is, in the control of the display device, a jump of the brightness which is prefixed by the slope m of the lines sl, s2 and that of the brightness which is prefixed by the minimum brightness Smin and by the maximum brightness Smax. However, since this takes place in the zone of minimum luminosity and in the zone of maximum luminosity, these changes of luminosity are on the one hand relatively rare

  and on the other hand imperceptible to the user.

  A limited number of different slopes m is prefixed for the control of the display device 4, so that memory space is saved in the memory 2 and furthermore, the calculation of the brightness of the display device 4 to 1 The first, second and third pairs of values are reduced to simple addition or substraction. The pentess are deposited in a table which is located in the

  memory 2 and to which the computing unit has access.

Claims (7)

  A method of adjusting the brightness of a display device (4), wherein the duty cycle of a pulse width modulated control signal is determined and a brightness control signal is set according to the ratio cyclic, this signal for controlling the brightness of the display device characterized in that a rising or falling edge of the control signal is detected and, as a function of this detection, a counter (9) is triggered at an initial time in that the overflows of the counter (9) are counted, in that a falling edge or the amount of the control signal is detected and, depending on this detection, at an intermediate time, the state of the counter ( 9) and the overflows of the counter (9) are stored in memory as an intermediate state, in that subsequently a rising or falling edge of the control signal is detected and, depending on this detection, at a final moment, the state of the counter (9) and the overflows of the counter (9) are stored in memory as a final state and in that from the ratio of the final state to the intermediate state, a cyclic ratio proportional to the ratio of the state   final intermediate state is determined.   2. Method according to claim 1, characterized in that, in the case of an overflow occurring almost simultaneously at a rising or falling edge, the state of the counter is examined and the overflow is recognized only when moment, the state of the counter is below a state which can be prefixed and in that the sidewall is recognized only when at this moment the counter state is above a state that can to be prefixed.   Method according to Claim 1, characterized in that, by means of the brightness control signal, a brightness value is read in a graph and in that the dependence between the brightness value and the brightness control signal is fixed by means of two straight lines which connect three pairs of prefixed values.   Method according to Claim 1, characterized in that, for a lower range of values and for a higher range of values of the brightness control signal, a constant brightness value is prefixed for each.   5. Method according to claim 3, characterized in that, for the lines, only a prefixed number of slopes are used.   6. Method according to claim 3, characterized in that the two straight lines, having slopes prefixed starting from the central pair of values, are oriented in the direction respectively of the   third and first pair of values.   7. A method according to claim 3, characterized in that it is first the range of values in which the duty cycle of the control signal falls which is determined, in that then a pair of values, preferably the pair. of values, is chosen, in that the difference between the duty cycle of the control signal and the value x of the chosen pair of values is determined, and in that the value y of the chosen pair of values the slope of the straight line of the domain in which the duty cycle falls is added or subtracted as often as is pre-set by the value of the difference and thus a value y which fixes the luminosity of the device is obtained visualization (4).