Abstract:
A device for activating a control unit is proposed. It includes at least one operating element operable by a user as well as analog encoding means assigned to the operating element. To generate an activation signal for a control unit, deactivation means are provided that deactivate at least one analog encoding means in order to digitally encode the operating element.

Description:
FIELD OF THE INVENTION 
     The present invention a device for activating a control unit according to the species defined in the independent claim. In automotive engineering, a plurality of operating elements are input in an analog manner in order to eliminate lines in a motor vehicle. In this context, depending on the control state of the operating elements, different voltages are generated at an analog input in that resistors different from the one used in the control unit are connected in series with the corresponding operating element. The resistor in the control unit and the resistor activated by the appropriate operating element form a voltage divider. The instantaneous state of the circuit elements and of the corresponding operating elements is able to be determined on the basis of the thus-established voltage. When one of the operating elements is operated, the activation operation of a control unit in rest mode is able to be introduced in order to power up the control unit. 
     BACKGROUND INFORMATION 
     If this operating element is encoded in an analog manner, an operating instance of the operating element would be able to be detected by a comparator or with the help of an analog-digital converter and a series-connected microcontroller. In the latter case, the microcontroller would either need to be permanently switched on for the voltage evaluation or regularly activated. This is associated with significant additional expenditure. However, if an operation is detected in connection with a comparator, the problem arises that voltage fluctuations, structural component tolerances, climatic influences, or also ageing or contamination cause the input level to shift so significantly that clear detection of a signal change is not able to be ensured over the entire lifetime. In particular, contamination of the operating element that is expressed, for example, in a parasitic resistor in parallel with the actual circuit element leads to problems regarding reliable operation detection. Therefore, an object of the present invention is to reliably detect operation of an analog encoded operating element in order to activate a control unit. 
     SUMMARY OF THE INVENTION 
     The device for activating a control unit of the present invention has at least one operating element able to be operated by a user. At least one analog encoding means is assigned to this operating element in order to detect operation of the operating element. In accordance with the present invention, deactivation means, which deactivate the analog encoding means and instead digitally, preferably binarily encode the operating element, are provided for generating an activation signal for a control unit Due to the clear, digital evaluation, operation of the operating element is able to be reliably detected even if different voltage levels or ageing processes significantly influence a signal encoded in an analog manner. Therefore, in particular, a comparator that compares the output signal influenced by the operating element with a fixed limiting value may be used for the evaluation. As a result of dispensing with a microcontroller for evaluating the signals, the need for closed-circuit current is able to be reduced. 
     In an advantageous further refinement, an electrical resistor is provided as the analog encoding means, a circuit element or a diode being connected in parallel thereto for its deactivation. If the control unit is in the normal mode, the operating elements are encoded in an analog manner. However, in the rest state of the control unit, the circuit element or the diode, being polarized in the forward direction, short-circuits the appropriate resistor or bridges it in a low-resistance manner. Due to the significantly reduced voltage drop, any operation of the operating element is able to be reliably detected. Not all analog encoding means have to be deactivated. For example, it could be provided for only the high-resistance resistors to be short-circuited. As such, it is ensured that when the operating element is operated, a sufficiently high voltage level is available for further evaluation for a possible activation of the control unit. 
     In an advantageous further refinement, a polarity-reversal means is provided for the purpose of deactivating the analog encoding means, the polarity-reversal means reversing the polarity of the diode in the rest state of the control unit in the forward direction, so that the appropriate analog encoding means is deactivated or short-circuited. In particular in the case of a plurality of operating elements connected in parallel, it may be achieved in a particularly simple manner that all analog encoding means are deactivated by simply reversing the polarity of the connection points. During normal operation of the control unit, the polarity-reversal means switch the diodes back to the blocking mode, so that the analog encoding is activated again. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a device according to the related art. 
         FIG. 2  shows a first exemplary embodiment. 
         FIG. 3  shows a first illustration of a second exemplary embodiment, once during normal operation of the control unit and once in the rest mode of the control unit. 
         FIG. 4  shows a second illustration of the second exemplary embodiment, once during normal operation of the control unit and once in the rest mode of the control unit. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  describes a device according to the related art. The four operating elements  31  through  34  shown by way of example are encoded in an analog manner by series resistors  21  through  24 , respectively. The series connection of first operating element  31  and first resistor  21 , second operating element  32  and second resistor  22 , third operating element  33  and third resistor  23 , and fourth operating element  34  and fourth resistor  24  is connected in parallel. The one connection is at ground  14 . The second connection is set to a positive potential  10  across a resistor  12 . It is also directed via an analog/digital converter  18  to a microcontroller  19  for further processing. Analog/digital converter  18 , microcontroller  19 , as well as resistor  12  are part of control unit  20 . Control unit  20  may be operated in a normal mode and in a rest mode. The rest mode is distinguished, for example, by a limited operating method that consequently necessitates little or no current. A contamination of operating elements  31  through  34  may result in a parasitic shunt resistor  16 , which appears, for example, at all operating elements  31  through  34 . 
     In the exemplary embodiment according to  FIG. 2 , circuit elements  41  through  44  are provided as deactivating means for analog encoding means  21  through  24 . Therefore, first circuit element  41  is connected in parallel with first resistor  21 , second circuit element  42  is connected in parallel with second resistor  22 , and so on. Otherwise, the configuration corresponds to that of  FIG. 1 . 
     In the exemplary embodiment according to  FIGS. 3 and 4 , diodes  51  through  54  are provided as the deactivation means. First diode  51  is connected in parallel with first resistor  21 , second diode  52  is connected in parallel with resistor  22 , and so on. In  FIG. 3 , diodes  51  through  54  are polarized in the blocking direction. As such, no current flows through diodes  51  through  54 , so that analog encoding means  21  through  24  are activated. Such a polarity reversal is provided during normal operation of control unit  20 . For this purpose, appropriate polarity-reversal means are situated between the connections and ground  14  and positive potential  10 , respectively. An output signal  11  reaches an analog input of control unit  20  that is not shown in greater detail. 
     The exemplary embodiment in  FIG. 4  differs from that in  FIG. 3  only in that polarity-reversal means  60  reverse the polarity of diodes  51  through  54  in the manner that they are then operated in the forward direction. Therefore, they are used as deactivation means for analog encoding means  21  through  24 . The current no longer flows across resistors  21  through  24  but across diodes  51  through  54 . This operating mode is provided for the rest mode of control unit  20 . Output signal  11  reaches a comparator  62 , which as a function of the comparison to a reference voltage  64 , generates a binary output signal for microcontroller  19  to activate the microcontroller. 
     In the related art ( FIG. 1 ), analog resistor encoding is shown for a plurality of operating elements  31  through  34 . In order to eliminate lead wires to the control unit  20  to be evaluated, operating elements  31  through  34  are connected in parallel with series resistors  21  through  24 , respectively. The resistance values of resistors  21  through  24  are selected differently in each case. As a result, when the user operates a certain operating element  31  through  34 , a voltage level characteristic for this operating element  31  through  34  is reached via the voltage divider that is formed from resistor  12  and resistors  21  through  24  activated in each case. This characteristic voltage level is provided to analog/digital converter  18  as an analog value. After the analog value is digitalized, microcontroller  19  is able to detect, for example by comparison with characteristic voltage levels, which of the operating element(s)  31  through  34  was/were operated. Corresponding functional sequences are initiated as a function of the operation. This described functionality occurs during normal operation of control unit  20 . 
     Parasitic shunt resistors  16  may occur due to ageing processes, for example. Since microcontroller  19  ensures a high degree of flexibility, ageing operations and voltage levels shifting as a result are able to be learned for the standard operation. However in the rest mode of control unit  20 , microcontroller  19  is to be deactivated in order to lower the need for closed-circuit current. Then other reliable evaluation methods for detecting operation of an operating element  31  through  34  are performed in order to activate control unit  20  in the case of operation of an operating element  31  through  34 , i.e., to bring it from the rest mode into normal operation. This is described in connection with  FIGS. 2 through 4 . 
     As seen in  FIG. 2 , circuit elements  41  through  44  are provided as deactivation means that are connected in parallel with respective resistor  21  through  24 . During normal operation of control unit  20 , the circuit elements are open, so that the functionality of an analog encoding of operating elements  31  through  34  already discussed in connection with  FIG. 1  is achieved. However, if control unit  20  is in the rest mode, circuit elements  41  through  44  are closed. As a result, analog encoding means  21  through  24  are short-circuited for their deactivation. At this point, operating elements  31  through  34  are encoded binarily. Due to the deactivation of the analog encoding means, the voltage change increases when an operating element  31  through  34  is operated to a greater extent than would be the case if analog encoding means  21  through  24  were still active. By suitably selecting reference voltage  64 , which establishes the comparator switching threshold, an operation of an operating element  31  through  34  is detected with a high degree of reliability. 
     Only an opening or a closing of any operating element is apparent from output signal  11 . Output signal  11  may, for example, be compared by comparator  62  to a reference voltage  64 . Reference voltage  64  is selected such that when any one of operating elements  31  through  34  is operated, the reference voltage is reliably exceeded. The output signal of comparator  62  changes its state when any operating element  31  through  34  is operated, thereby activating microcontroller  19  and, consequently, control unit  20 . For example, a door handle contact of a motor vehicle could be provided as operating element  31  through  34 . Therefore, control unit  20  is already activated when the door handle is operated. As such, the powering-up operation of control unit  20  is already able to be successfully completed when the driver wishes to start the vehicle. Any other sufficiently known operating elements may also be evaluated in the manner described. 
     In the exemplary embodiment according to  FIGS. 3 and 4 , diodes  51  through  54  are provided as the deactivation means. They essentially satisfy the same conditions as circuit elements  41  through  44  in  FIG. 2 . In  FIG. 3 , diodes  51  through  54  are polarized in the blocking direction, so that the desired analog encoding is available during normal operation of control unit  20 . However, if control unit  20  is in the rest mode, diodes  51  through  54  are polarized in the forward direction. As such, they bridge resistors  21  through  24  to deactivate them. This is achieved by polarity-reversal means  60 . The polarity-reversal means could, for example, have corresponding circuit elements in order to ensure the desired polarity reversal. A bridge connection made up of four additional circuit elements is suitable for this. Polarity-reversal means  60  are able to be integrated in control unit  20 . 
     Microcontroller  19  is able to control the deactivation or activation of the analog encoding as a function of a command signal on the basis of which control unit  20  enters the rest state. The signal “ignition on/off” is also suitable for this purpose. If the vehicle is turned off via the signal “ignition off,” the deactivation of the analog encoding is able to be triggered by this signal. At the latest when the signal “ignition on” occurs the analog encoding is again permitted. 
     It is not absolutely necessary for every resistor  21  through  24  to be short-circuited. However, it is particularly advantageous when resistors  21  through  24  are relatively high-resistance in comparison with the contaminant resistors/capacitive shunt resistors  16 . 
     Although as a result of the indicated configuration, the evaluation is preferably able to be performed by a comparator  62 , an analog/digital converter  18  having a series-connected microcontroller  19  is also conceivable. The evaluation reliability is also increased in this case.