JP2675488B2 - Electronic device key input detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a key input detecting device for an electronic device which detects a key switch operated by the microcomputer by inputting an analog signal having a different voltage level to each key switch operated by the microcomputer. Regarding

[0002]

2. Description of the Related Art Most of recent electronic devices are equipped with a microcomputer so that the entire system can be controlled by the microcomputer. Normally, a plurality of key switches for input are used to perform various controls. It is provided.

In such an electronic device, a key input detecting device configured to detect an operated key switch by a microcomputer is provided. As the key input detecting device, each key switch operated is provided. Analog signals of different voltage levels are generated in the
It is known to use a device provided with a digital converter and detect a operated key switch based on a voltage level of an input analog signal. It suffices if a microcomputer is provided with a single analog input terminal in order to detect a plurality of key switches by using such a key input detection device.

By the way, there is known an electronic device using a battery as a power source in order to make it portable and portable. In such an electronic device, generally, the power supply to each circuit is managed by the microcomputer, and the state in which the operation of the microcomputer is stopped is the power-off state. Therefore, in such an electronic device, a power supply switch is omitted, and a control signal for instructing reproduction is generated by operating another main operation switch, for example, a reproduction switch in the case of a music reproduction device. , There is one configured to generate a start signal for starting a microcomputer.

[0005]

By the way, in the past, the configuration was such that the microcomputer was started by only a predetermined single switch, but depending on the electronic device, it is convenient to start the microcomputer at the same time. On the other hand, the number of the microcomputers is not always one. On the other hand, if the microcomputers are simultaneously activated by all operations, the microcomputers are unnecessarily operated, which is not preferable in terms of malfunction and power consumption.

Further, as described above, in the electronic device configured to detect the key switch operated on the basis of the voltage level of the input analog signal, the voltage level becomes equal to or lower than a predetermined value set in advance. Providing a low voltage detection circuit for detecting a low voltage so that only the minimum voltage level of the analog signal generated when a plurality of key switches is operated falls below the set voltage level of the low voltage detection circuit. It is possible to determine the key switch that minimizes the voltage level of the analog signal generated when the key switch is operated. The key switch identified in this way is
It can be limited to a specific key switch that can activate the microcomputer.

However, in an electronic device that uses a battery as a power source, when the power source voltage drops due to exhaustion of the battery, the low voltage detection circuit constantly detects the low voltage, and accordingly, the battery discharge system. There was a problem that the road was formed and the battery was over-discharged.

[0008]

SUMMARY OF THE INVENTION The present invention provides a key input detecting device for an electronic device, which is made in view of the above-mentioned problems, in which a resistor voltage divider for dividing a power supply voltage is provided with a plurality of key switches. Key input means configured by incorporating each key switch, and an analog input terminal provided in a microcomputer to which analog key input signals of different voltage levels are input according to the operated key switch of the key input means, Input key detecting means for detecting a key switch operated based on a key input signal input to the analog input terminal, and detecting that the voltage level applied to the analog input terminal is a low voltage below a predetermined value. And a low voltage detection circuit for generating a detection output for selectively activating the microcomputer based on the detection, and low voltage detection by the low voltage detection circuit. The bell is a voltage level in the middle of the voltage level range generated when each key switch of the key input means is operated, and each voltage level generated when a plurality of predetermined key switches of the key input means are operated. It is set to be larger.

Further, in addition to the above-mentioned constitutional requirements, a switching transistor for selectively generating an activation signal for activating the microcomputer in accordance with a detection output by a low voltage detection circuit, and a minimum voltage level for turning on the switching transistor. And a constant voltage element for adjusting the power supply voltage, the switching transistor is turned on when the power supply voltage decreases and the low voltage detection circuit is in a state where low voltage detection is performed irrespective of the operation of the key input means. This prevents the load resistor connected to the switching transistor from discharging the battery.

[0010]

According to the present invention, the key switch operated is detected by inputting analog key input signals having different voltage levels to the microcomputer according to the operation of each key switch. A low voltage detection level is set by the low voltage detection circuit in order to determine a plurality of predetermined key switches having a lower voltage level of the key input signal generated when the switch is operated, and the low voltage detection level is set by the low voltage detection circuit. When the key switch is detected, the microcomputer is activated, and when each of the plurality of predetermined key switches is operated, the control assigned to each key switch is performed and the microcomputer is activated.

Further, according to the present invention, a switching transistor whose on / off is controlled according to a detection output from a low voltage detection circuit is used to generate a start signal for starting a microcomputer. Then
Adjusting the minimum voltage level for turning on the switching transistor in order to prevent the switching transistor from being turned on when the low voltage detection circuit is in a state where low voltage detection is performed regardless of the operation of the key switch. A constant voltage element is connected to prevent the battery from being discharged by the load resistance connected to the switching transistor.

[0012]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
Is a battery serving as a power source, 2 is a resistance voltage divider composed of a plurality of resistors 3, 4, 5, 6 connected in series between the battery 1 and ground, and 7 is between the connection point of each resistance of the resistance voltage divider 2 and ground Is a key input means composed of a plurality of key switches connected to each other, that is, a first key switch 8, a second key switch 9, a third key switch 10 and an Nth key switch 11.

Reference numeral 12 is a microcomputer having a power supply terminal 13 for obtaining an operating voltage from the battery 1 and controlling various controls. The microcomputer 12 is provided with an analog / digital conversion function for converting an analog signal into a digital signal, and key input means for generating a key input signal having a voltage level according to the operation of each key switch of the key input means 7. 7
The analog input terminal 14 connected to the output point A is provided. Further, the microcomputer 12 has an interrupt request terminal 15 for receiving an interrupt request, and when the digital signal level applied to the interrupt request terminal 15 becomes "L" level, the "L" level signal is used as a start signal. When the microcomputer 12 is in the sleep mode in which the operation of the microcomputer 12 is stopped, the microcomputer 12 is activated by applying the "L" level signal to the interrupt request terminal 15.

Reference numeral 16 is an input key detecting means provided in the microcomputer 12 for detecting a key switch operated based on a voltage level applied to the analog input terminal 14,
Is a low voltage detection circuit for detecting that the voltage level applied to the output point A of the key input means 7 , that is, the analog input terminal 14 is a low voltage below a predetermined value.

The output of the low voltage detection circuit 17 is held at the "H" level which is the power supply voltage of the battery 1,
It is stable in the state where the "H" level signal is generated,
When a low voltage is detected, it temporarily becomes the ground voltage level "L" level, and a pulse-like "L" level signal is generated.

An NPN type 18 has a collector connected to the battery 1 via a load resistor 19, an interrupt request terminal 15 of the microcomputer 12, and an emitter connected to the output terminal of the low voltage detection circuit 17. The switching transistor 20 is a Zener diode having a cathode connected to the battery 1 and an anode connected to the base of the switching transistor 18 via a base resistor 21.

Next, the operation will be described.

When none of the key switches of the key input means 7 is operated, the output point A of the key input means 7 is disconnected from the ground, so that the output point A
The power supply voltage of the battery 1 is generated in the battery.

On the other hand, when each key switch of the key input means 7 is operated, one of the voltage dividing points, which is a connection point of each resistance of the resistance voltage divider 2 , is grounded via the operated key switch.

In this case, when the first key switch 8 whose one end is directly connected to the output point A is operated, the output point A is grounded, so that the ground voltage level "0" is applied to the output point A.
Occurs. Then, as the resistance of the resistance voltage divider 2 interposed between one end of the key switch and the output point A increases, the voltage level generated at the output point A when each key switch is operated increases. When the Nth key switch 11, one end of which is connected to the end of the resistance voltage divider 2 , is operated, the voltage level generated at the output point A constitutes the resistance 3 and the resistance voltage divider 2 excluding the resistance 3. All resistors 4, 5,
6, the maximum voltage division level Vmax is obtained by dividing the power supply voltage of the battery 1.

Therefore, when each key switch of the key input means 7 is operated, at the output point A, depending on the operated key switch, as shown in FIG. 2, from the ground voltage level 0 to the maximum voltage division level Vmax. Key input signals having different voltage levels are generated within the voltage level range up to.

The resistances constituting the resistance voltage divider 2 are set so that the voltage levels of the key input signal generated at the output point A are dispersed with an appropriate potential difference, and the voltage levels are different. Based on the above, the detection of the key switch operated by the input key detecting means 16 is ensured.

The critical voltage Vc, which is the maximum voltage level of the low voltage detection level detected by the low voltage detection circuit 17, is
As shown in FIG. 2, the voltage level generated at the output point A when the second key switch 9 is operated and the third key switch 1
It is set in the middle of the voltage level generated at the output point A when 0 is operated. Therefore, the low voltage detection circuit 17 is the first of the key switches of the key input means 7 .
Only when the key switch 8 and the second key switch 9 are operated, it is detected that the key input signal generated at the output point A has a low voltage.

Since the low voltage detection circuit 17 does not detect a low voltage when none of the key switches of the key input means 7 is operated, the output is held at "H" level. Here, since the “H” level is the power supply voltage of the battery 1, the switching transistor 1
8 is reverse biased and held in the off state. Therefore, in this state, the power supply voltage of the battery 1, that is, the “H” level signal is applied to the interrupt request terminal 15 of the microcomputer 12 through the load resistor 19.

Now, when the key switch of the key input means 7 is operated and a key input signal of a voltage level corresponding to the operated key switch is generated at the output point A, the key input signal is an analog input of the microcomputer 12. The voltage is applied to the terminal 14 and input to the low voltage detection circuit 17.

If the operated key switch is the first key switch 8 or the second key switch 9,
The low voltage detection circuit 17 detects a low voltage and generates an "L" level signal. Therefore, the switching transistor 18
Becomes the ground voltage level, and the switching transistor 18 is forward biased. In this case, when the battery 1 is not excessively consumed and a power supply voltage sufficient to operate each circuit is obtained, the base voltage obtained by subtracting the Zener voltage of the Zener diode 20 from the power supply voltage is switched. The switching transistor 18 is turned on because it is sufficiently higher than the rising voltage between the base and the emitter of the transistor 18.

When the switching transistor 18 is turned on, the "L" level signal is applied to the interrupt request terminal 15 of the microcomputer 12, so that the microcomputer 12 is activated. Therefore, the key input signal applied to the analog input terminal 14 is supplied to the input key detecting means 16, the key switch operated by the input key detecting means 16 is detected, and the control operation corresponding thereto is started.

On the other hand, if the operated key switch is a key switch other than the first key switch 8 and the second key switch 9, the low voltage detection circuit 17 does not detect a low voltage,
The "H" level signal is still generated. Therefore, the switching transistor 18 is in the off state,
The "H" level signal is still applied to the interrupt request terminal 15 of the microcomputer 12.

Therefore, if the microcomputer 12 is not activated, the key input signal applied to the analog input terminal 14 by the operation of the key switch is not accepted and no control operation is performed.
Is already activated, the key input signal applied to the analog input terminal 14 by the operation of the key switch is supplied to the input key detecting means 16, and the key switch operated by the input key detecting means 16 is supplied. A corresponding control operation is performed.

Specifically, when the circuit of FIG. 1 is used for a CD player, the first key switch 8 which is turned on at the same time as the play switch for starting reproduction is also turned on. If the two-key switch 9 is made to correspond to a mode change-over switch for selectively designating access, program selection, repeat and intro scan by cyclic operation, usability is improved.

By the way, when the battery 1 is exhausted and the power supply voltage drops, the low voltage detection circuit 17 detects the low voltage even if the key switch of the key input means 7 is not operated. In this case, the low voltage detection circuit 17 generates an "L" level signal. However, as the Zener diode 20, a Zener diode having a Zener voltage set in consideration of the voltage level of the low voltage detected by the low voltage detection circuit 17 is used, and the low voltage detection circuit 17 is used.
The voltage level of the low voltage detected by is selected to be lower than the voltage level obtained by adding the Zener voltage of the Zener diode 20 and the rising voltage between the base and emitter of the switching transistor 18, so that the low voltage detection circuit 17 The switching transistor 18 is not turned on even when the output becomes "L" level.

Therefore, even if a low voltage is detected by the low voltage detection circuit 17 due to a drop in the power supply voltage, the switching transistor 18 is not turned on and the load resistance 1
The battery 1 is never consumed by 9.

[0033]

As described above, according to the present invention, by using the low voltage detecting circuit, a plurality of predetermined ones having a lower voltage level of the key input signal generated when each key switch of the key input means is operated. So that the key switch of
It is possible to provide a key input detection device for an electronic device that can activate a microcomputer when the determination is made. Also,
According to the present invention, it is possible to prevent the switching transistor for generating the start signal for starting the microcomputer from being turned on when the low voltage detection circuit is in the state of detecting the low voltage due to the decrease of the power supply voltage. Therefore, at this time, the battery is prevented from being discharged by the load resistance connected to the switching transistor, and the battery can be prevented from being over-discharged.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining the circuit of FIG.

[Explanation of symbols]

1 Battery 2 Resistance voltage divider 7 Key input means 12 Microcomputer 14 Analog input terminal 15 Interrupt request terminal 16 Input key detection means 17 Low voltage detection circuit 18 Switching transistor 19 Load resistance 20 Zener diode

Claims (2)

(57) [Claims] 1. An electronic device including a microcomputer that controls in response to an operation of a key switch, and a key input unit configured by incorporating each key switch of a plurality of key switches into a resistance voltage divider that divides a power supply voltage, Based on an analog input terminal provided in a microcomputer to which an analog key input signal having a different voltage level is input according to the operated key switch of the key input means, and a key input signal input to the analog input terminal Input key detection means for detecting an operated key switch, and detection that the voltage level applied to the analog input terminal is a low voltage below a predetermined value, and selectively starts the microcomputer based on the detection. A low-voltage detection circuit for generating a detection output for controlling the low-voltage detection level by the low-voltage detection circuit. It is characterized in that the voltage level is set in the middle of a voltage level range generated when the key switch is operated and higher than each voltage level generated when a plurality of predetermined key switches of the key input means are operated. Key input detection device for electronic equipment. 2. A key input means in which each key switch of a plurality of key switches is incorporated in a resistance voltage divider that divides a power supply voltage in an electronic device that uses a battery as a power source and is controlled by a microcomputer. An analog input terminal provided in a microcomputer to which an analog key input signal having a different voltage level is input according to the operated key switch of the key input means, and an operation based on the key input signal input to the analog input terminal Input key detecting means for detecting the activated key switch, a low voltage detecting circuit for detecting that the voltage level applied to the analog input terminal is a low voltage below a predetermined value, and a detection output by the low voltage detecting circuit. A switching transistor for selectively generating a start signal for starting the microcomputer according to A constant voltage element for adjusting the minimum voltage level for turning on the transistor is provided, the power supply voltage has dropped, and the low voltage detection circuit is in a state in which low voltage detection is performed regardless of the operation of the key input means. At this time, the switching input transistor is prevented from being turned on, and the battery resistance is prevented from being discharged by the load resistance connected to the switching transistor.