JPH04113367A - Switch input detection device - Google Patents

Abstract

PURPOSE:To surely detect the ON/OFF states of respective operation switches by making a constant current flow to the resistances of a switch input circuit and the operation switches through a constant current circuit. CONSTITUTION:When one operation switch SWi is turned ON, the current from a power terminal Vref flows through the resistances R1-Ri and operation switch SWi and then flows to a ground power source through the constant current circuit 2. Therefore, the voltage Vout at an output terminal connected to a common line 1 is represented as Vout=Vref-SIGMARXI0, where Vref is a source voltage, I0 is the constant current of the constant current circuit 2, and SIGMARi is the sum of the resistance values of the resistances R1-Ri. Consequently. the voltage developed at the terminal Vout is higher and higher as the switch SW which is turned ON is closer and closer to the terminal Vref. Then a microcomputer the voltage at the terminal Vout with a decision levels set corresponding to respective switches SW to decide which switch SW is turned on. Therefore, a current flowing to a constant is invariably constant without reference whether an operated switch is close to or remote from the power source.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a switch input detection device for electronic equipment such as a copying machine, a facsimile machine, etc., which has a plurality of operation switches.

(Prior art) In electronic devices such as copying machines that have a large number of operation switches, if a detection line is provided for each operation switch to detect 0N10FF of the switch, the number of harnesses will be too large, which will increase the cost of the device. It becomes impossible to avoid close-ups.

Therefore, conventionally, a switch input detection device having a switch input circuit as shown in FIG. 5 has been provided. In this switch input circuit, a large number of resistors R+ to R0 are power terminals ■,
. connected in series without Further, one end of the same number of operation switches SW + to SWn is connected to each of these resistors R1.
-Rn and the other end of the resistor Rrl. The other ends of these operation switches SW1 to SWo are connected to each other by a common line 1 and further grounded via a resistor R181.

In the conventional switch input circuit as described above, when one of the operation switches sw1 is operated and turned ON, the current from the power supply terminal Vl@( is connected to the resistors R1 to R1 and the operation switch S
It flows into the ground power supply through W1 and resistor R1111. Therefore, at this time, the output terminal ■ is connected to the common line 1. , t can be expressed by the following equation, assuming that the sum of the resistance values of the resistors R1 to R1 is ΣR1.

V out= (R121/ (ΣR++R+in)
) X Vrer and this output terminal■. , t, as shown in FIG. The closer the operating switch SW is turned on, the higher the voltage becomes. For this reason, the output terminal ■. By determining the voltage of ut with a voltage determination circuit (not shown), it is possible to detect which operation switch SW has been operated.

In some cases, a plurality of switch input circuits shown in FIG. 5 are provided, and the inputs of even more operation switches SW are detected by sequentially applying power to each power supply terminal Vrej by scanning.

(Problems to be Solved by the Invention) The conventional switch input detection device described above, as shown in FIG. When operating the operation switch SWI etc. close to f, the output terminal ■ is sent to the adjacent operation switch SW. The voltage change Δ■ of ut also becomes large, and the operation switch SW can be easily determined. However, the operation switch SWo that is far from the power supply terminal
etc., when operating the output terminal ■. ut voltage change △V
is small (and, moreover, since ΣR1, which determines the voltage at the output terminal Therefore, in the conventional switch input detection device, each resistor R1 to R1, RI
Use a highly accurate A/D converter in the il+ or voltage determination circuit, or use the power supply terminal v r,
There was a problem in that it was necessary to limit the number of operation switches SW connected between the power source and the ground power source.

Further, in order to operate the operation switch SW stably, it is necessary to make the voltage between the contacts when it is OFF and the current that flows through the contacts when it is ON be a predetermined value or more.

However, in the conventional switch input detection device, the current flowing through the contacts of the operation switch SW becomes smaller in the operation switch SW far from the power supply terminal v ror, so that the operation of such an operation switch SW becomes unstable. There was also the problem of ease of use.

In view of the above-mentioned circumstances, the present invention allows a constant current to flow through the resistance of the switch input circuit and the operation switch.
It is an object of the present invention to provide a switch input detection device that can reliably determine the operation of an operation switch using a voltage determination circuit.

(Means for Solving the Problems) The switch input detection device of the present invention includes one end of a plurality of operation switches whose other ends are both connected to an output terminal, or a plurality of resistors connected in series to one end of a power supply. The output terminal of the other end of the operation switch is connected to the other side of the power supply ☆:1'4 via a constant current circuit, and a voltage determination circuit is connected to the output terminal. connected, thereby achieving the above objective.

Further, the switch input detection device of the present invention is a switch input detection device that detects which of a plurality of operation switches has been operated by comparing a voltage appearing at an output terminal with a determination level, and which detects which of a plurality of operation switches has been operated. The switch includes voltage detection means for detecting the voltage at the output terminal when a predetermined one of the switches is operated, and judgment level correction means for correcting the judgment level for other operation switches based on the detected voltage. .

(Function) With the above configuration, when a certain operation switch is operated and turned ON, current flows through all the resistors connected to one end of the power source from the operation switch.

Moreover, a constant current flows through these resistors due to the constant current circuit, so the power supply voltage is reduced to ■. ``Constant current I8
If the sum of the resistance values in the resistance through which the current flows is ΣR, then the voltage at the output terminal is ■. , t are shown by the following formula, and V out=
V rer-Σ RXI[l is proportional to the sum of resistance values ΣR. Therefore, regardless of whether the operating switch is near or far from one end of the power supply, the voltage at the output terminal can be sufficiently changed relative to the adjacent operating switch, so the voltage judgment circuit can make reliable judgments. You will be able to do this. In addition, the operation switch can be turned off.
Since the voltage between the contacts at the time of operation and the current flowing through the contacts at the time of ON are always constant regardless of the distance from one end of the power supply, each operation switch can perform stable operation.

Note that if an operation switch that is far from one end of the power supply is turned on, the voltage at the output terminal is determined by the sum of the resistance values of many resistors, so errors in the resistance values of the resistors used will accumulate. . For this reason, for example, the resistance value of each resistor may be made to gradually increase as the distance from one end of the power supply increases, so that the voltage determination circuit can make a determination with more margin.

Furthermore, when the output voltage is detected by the voltage detection means,
The determination level is corrected at any time based on this detected voltage by the determination level correction means, taking into consideration errors in the resistance value of each resistor, changes over time, changes in contact resistance of the operation switch, and the like.

(Example) The invention will now be described with reference to examples.

1 to 4 show an embodiment of the present invention, in which FIG. 1 is a circuit diagram of a switch input circuit in a switch input detection device, and FIG. 2 is a circuit diagram of a voltage determination circuit in a switch input detection device. In the block diagram, FIG. 3 is a graph showing the relationship between the operation of each operation switch and the output voltage, and FIG. 4 is a graph showing the allowable range of the judgment level in the voltage judgment circuit.

Components having the same functions as those of the conventional example shown in FIG. 5 are given the same reference numerals.

This embodiment is a switch input detection device used in a copying machine. As shown in FIG. 1, the switch input circuit in this switch input detection device includes a large number of resistors R1 to R1.
, are connected in series to the power supply terminals v r, ,. Further, one end of the same number of operation switches SW I- and SWn is connected between these resistors R1 and Rn and to the other end of the resistor R1, respectively. And these operation switches SW 1
The other ends of ~SWn are connected to each other by a common line 1. This common line 1 is the output terminal V. ut and is also grounded via a constant current circuit 2.

The constant current circuit 2 includes an operational amplifier 2a (op-amp), a transistor 2b, and a resistor R21! The collector terminal of the transistor 2b is connected to the common line 1, and the emitter terminal of the transistor 2b is grounded via the resistor R21!1. The operational amplifier 2a has a non-inverting input terminal and a power supply terminal (2). The voltage of f is divided by resistor R2θ2 and resistor R2113 and inputted, and the voltage drop across resistor R2θ1 is inputted to the inverting input -, and the output is inputted to resistor R21+.
4 to the base terminal of the transistor 2b. Therefore, the operational amplifier 2a controls the transistor 2b so that the voltage drop across the resistor R2i11 becomes equal to the divided voltage across the resistors R2112 and R2B3 due to an imaginary short circuit, and as a result, the current flowing through the common line 1 is made to be a constant current.

The above output terminal ■. As shown in FIG. 2, ut is connected to the analog input terminal AN of the analog input section 3a of the microcomputer 3 constituting the voltage determination circuit. In addition, the analog input section 3 of the microcomputer 3
a is the analog power supply terminal VAN and the above power supply terminal ■. f
At the same time, the analog ground terminal GN DAN is grounded so that the voltage of the power supply terminal v r, , in the circuit of FIG. 1 is inputted as a reference voltage. The analog input section 3a of the microcomputer 3 converts the input voltage into digital data by A/D conversion, and converts the input voltage into digital data.
This is an analog interface that inputs to the CPU through 10 ports. And this microcomputer 3
is the output terminal ■ that receives input from the analog input terminal AN. u
By comparing the voltage at t with each determination level stored in the internal ROM or RAM, it is possible to determine which operation switch SW in the switch input circuit is turned on.

It should be noted that a plurality of switch input circuits shown in FIG. ut to the analog input terminal AN of the microcomputer 3, and by sequentially applying power to the power supply terminal Vrer of each circuit by scanning, the inputs of even more operation switches SW can be detected. You can also do it.

The switch input detection device having the above configuration has a power supply terminal V that is turned on when any of the operation switches SW + is operated.
,. The current from f flows through resistors R1 to R1 and operation switch S.
It passes through W+ and flows into the ground power source via the constant current circuit 2. Therefore, at this time, the output terminal ■ is connected to the common line 1. The voltage of ut (■.ut) is the power supply voltage V
rel, the constant current of constant current circuit 2 is T, and the resistance R is
Letting the sum of the resistance values of 1 to R1 be ΣR, it is expressed by the following equation.

V out-V tar-ΣR,XIg Therefore, the output terminal ■. The closer the turned ON operation switch SW is to the power supply terminal V r e f , the higher the voltage will be output from the ui. And in microcomputer 3,
This output terminal V. , t is compared with a determination level set according to each operation switch SW to determine which operation switch SW is turned on. Note that if two or more operation switches SW are operated at the same time, the power terminals ■,. ``The operation of the operation switch sw closest to ``is detected.

When the above switch input detection device operates, the output terminal ■. ,
As shown in the above equation, the voltage at t decreases in proportion to the total resistance value ΣR. Therefore, for example, each resistor R
, -Ro are set to the same resistance value, this output terminal ■.

, t, as shown in FIG.
The voltage change Δ■ becomes equal for the operation of W+ to SWn. Therefore, the microcomputer 3 can reliably determine the operation switch SW that is turned on, regardless of its distance from the voltage tX terminal 1°F.

In addition, when each operation switch SW is OFF, the pressure between the contacts is 12, and when the switch is ON, the current flowing through the contacts is the power supply terminal v.
Since it is always constant regardless of distance from r or r, each operation switch SW can perform stable operation. As a result, the A/D of microcomputer 3
Assuming that the converter has an 8-bit resolution, the fifth
In the conventional switch input circuit shown in the figure, normally 4 to 5 operation switches SW can be connected per line, but in this embodiment, 13 to 15 operation switches SW can be connected to one line. You will be able to connect.

When the operation switch sW that is far from the power supply terminal Vr6 is turned on, the voltage of the output terminal Vout is determined by the sum of the resistance values of many resistors R1 to R1, so the resistance values of the resistors R1 to R1 used For this reason, the resistance value of each resistor R1 to R, is made to gradually increase as it moves away from the power supply terminals R, and the judgment is made according to each operation switch SW in the microcomputer 3. As shown in FIG. 4, the power supply terminal Vre
If the operation switch SW farthest from r is set to have a wide tolerance range, more reliable determination can be made. However, each allowable range for each operation switch SW needs to be set at a certain interval or more so that they do not overlap with each other.

In addition, in this embodiment, the resistors R1 to R1, R28
In addition to errors in the resistance values of 1 to R284, consideration is given to changes in these resistance values over time, changes in contact resistance in the operation switch SW, etc., and as described above, the determination level of each operation switch SW in the microcomputer 3 is adjusted to a certain extent. It is necessary to establish a tolerance range. For this reason, the power supply terminal V4. "
Although the number of operation switches sW that can be connected to one line between
There is a limit to this number. Then, the operation switch SW is operated and the output terminal ■. Every time the voltage of ut is judged by the microcomputer 3, if the judgment level is corrected so that the voltage value at that time is set as the median value, the judgment can be made in response to errors in resistance values, changes over time, etc. You will be able to do this. As a result, the allowable range of the determination level in the microcomputer 3 can be narrowed, so that it is possible to connect and detect even more operation switches. In addition, this judgment level correction is not performed every time each operation switch SW is operated, but when any one operation switch SW is operated, or when the first operation is performed when the copying machine is turned on. By performing this only on the switch SW, the burden on the microcomputer 3 can be reduced. In this case, since a change in one operation switch SW often affects all operation switches SW in the same way, the judgment level of the non-target operation switch SW is also corrected to the judgment level of the target operation switch SW. Just slide it to correct it. The first operation switch SW to be corrected is the power terminal ■.

If you set the operation switch SWo farthest from f,
It is possible to cope with all aging changes of the resistors R1 to Ro. Further, the key may be set to a copy key, clear key, etc. that are frequently used in a copying machine.

(Effects of the Invention) As is clear from the above explanation, according to the switch input detection device of the present invention, it is possible to reliably detect 0N10FF of each operation switch. It is no longer necessary to use high-performance parts, and the number of harnesses can be further reduced by increasing the number of operation switches connected between the power supplies, so the cost of the device can be reduced.

4.Fig. Theory I Figures 1 to 4 show an embodiment of the present invention, in which Figure 1 is a circuit diagram of a switch input circuit in a switch input detection device, and Figure 2 is a circuit diagram of a switch input circuit in a switch input detection device. A block diagram of the judgment circuit, Fig. 3 is a graph showing the relationship between the operation of each operation switch and the output voltage, Fig. 4 is a graph showing the judgment level in the voltage judgment circuit, and Figs. 5 and 6 are conventional examples. 5 is a circuit diagram of a switch input circuit in a switch input detection device, and FIG.
The figure is a graph showing the relationship between the operation of each operation switch and the output voltage.

2... constant current circuit, 3... microcomputer (
Voltage judgment circuit, judgment level correction means), ■. . T...
Output terminal, SW...operation switch, Vr6r...power supply, R1-Rn...resistance.

that's all

Claims (1)

[Claims] 1. One end of a plurality of operation switches whose other ends are both connected to an output terminal is connected between each resistor or to a resistor end of a plurality of resistors connected in series to one end of a power supply. , a switch input detection device in which an output terminal on the other end side of the operation switch is connected to the other end of a power source via a constant current circuit, and a voltage determination circuit is connected to the output terminal. 2. A switch input detection device that detects which of a plurality of operation switches has been operated by comparing a voltage appearing at an output terminal with a determination level, the switch input detection device detecting whether a predetermined one of the operation switches has been operated. A switch input detection device comprising voltage detection means for detecting a voltage at an output terminal when a switch is input, and judgment level correction means for correcting judgment levels for other operation switches based on the detected voltage.