JPS5852599B2 - touch response circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a touch response circuit that can obtain an output voltage that changes depending on the speed of key depression.

Conventionally, as a circuit of this type, the one shown in FIG. 1, which utilizes charging and discharging of a capacitor, is known.

In Fig. 1, the mover C of the key press circuit KSW is always in contact with the terminal a (charging side terminal) on the power supply side B, and the capacitor C
8 is charged to +B voltage.

When the mover C of the key press switch KSW moves into contact with the terminal from which the touch response voltage is obtained by pressing the key, the terminal voltage hardly changes as shown in the discharge characteristics of the capacitor C6 shown in FIG.

This is because a discharge resistor is not connected to the capacitor co, and a leakage current flows.

Therefore, there is almost no difference in the touch response voltage obtained from the terminal when the key press switch KSW is activated due to a slow key press or when a key is pressed quickly, so the voltage corresponding to the speed of the key press is obtained. The touch response characteristics are not as good as the so-called dynamic range.

Therefore, an attempt was made to widen the dynamic range by connecting a low resistance element R1 to the capacitor C1, as shown in FIG.

As shown in FIG. 4, the discharge characteristics in this case are such that the charge stored in the capacitor C1 since the movable element C leaves the terminal a is rapidly discharged by the resistive element R1.

Therefore, when the slider C comes into contact with the terminal, the capacitor C
The terminal voltage (■) of No. 1 was much lower than the charging voltage.

If the movement of the movable element 0 is extremely fast, the terminal voltage V should also become large, but it is actually a finite value.

Also, if the value of the resistor R1 is increased, the characteristics shown in Figure 2 will be approached, so since the value of the resistor R1 is relatively small, the voltage obtained will be considerably lower than vB even if the key speed is high. It was not possible to obtain a touch response voltage that varied sufficiently depending on the difference in values and had a large value, and as a result, the dynamic range was not wide enough.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks and to provide a touch response circuit that can provide a large output voltage with different values depending on the speed of key depression.

Embodiments of the present invention shown in the drawings will be explained below.

FIG. 5 is a circuit diagram explaining the principle of the present invention, in which the resistor R2
is a large value that forms a first resistor circuit and does not substantially discharge the charge charged in the capacitor C2, and the resistor R3 is a second resistor.
A resistor circuit is formed, and a low resistance similar to the resistor R1 in FIG. 3 is selected.

Therefore, the time constant is R3·C2 (R2·C2).

The switch S is connected in series with the resistor R3 and is closed when the mover C of the key press switch KSW leaves the terminal a and the capacitor C2 is discharged to a predetermined level.

In this case, the predetermined level is the time t0 elapsed when the mover C leaves the charging side terminal a and contacts the terminal from which the touch response voltage is obtained when a normal person presses the key at maximum speed, as shown in Fig. 6. The capacitor voltage +vD when

Therefore, when the key press is extremely fast, the touch response voltage, ie, the terminal voltage of the capacitor C2, obtains a vDO value with almost no difference compared to the charging voltage of 10 vB.

If the key is pressed a little later, the time it takes for the slider C to leave terminal a and contact b will take longer than tl, so capacitor C2 will start discharging via resistor R3.
The touch response voltage obtained at that time is much smaller than +■o.

Therefore, the discharge curve of the capacitor C2 as shown in FIG. 6 is obtained, and a touch response voltage that varies greatly depending on the key speed is obtained.

Note that in FIG. 5, it is not necessary to connect the resistor R2, and the resistance when the switch S is opened may be used.

Next, FIG. 7 shows a specific circuit diagram for realizing the circuit of FIG. 5, and the value of the operating voltage vD of the transistor Tr is set to the voltage 2 at time t1 in FIG.

be selected. That is, vD <VB, and VB is the power supply voltage for charging the capacitor C2.

The transistor Tr1 operates as the switch S shown in FIG.

In addition, the value of resistor R4 + R5 is selected as the value of R2 in Fig. 5,
In addition, the base voltage of the transistor Tr2 is the same as that of the capacitor C2.
R4<R5 is selected so that it does not become smaller than VD during charging.

When the mover C leaves the terminal a, the terminal voltage of the capacitor C2 gradually discharges through the resistors R4 and R5.

When time t in FIG. 6 is reached, the base voltage of the transistor Tr2 becomes equal to the collector voltage VD.

After that, the base voltage of Tr2 decreases below VD, and Tr2
is conductive, so the base voltage of transistor Trl rises from zero, making Trl conductive.

Therefore, the charge in the capacitor C2 is rapidly discharged via the resistor R3 and the transistor Trl.

When the key speed is fast, a voltage close to vD is obtained as the touch response voltage, and when the key speed is slow, a voltage much smaller than vD is obtained as the touch response voltage.

In this way, according to the present invention, a large value is obtained as the touch response output voltage when the keying speed is fast, and a small output voltage is obtained when the keying speed is slow, and a touch response circuit is obtained in which the output voltage varies greatly depending on the keying speed. This made it possible to make the so-called dynamic range extremely wide.

In the past, because the discharge was quick immediately after the key press switch operated, sufficient mechanical accuracy was required for the mover C of the switch to move from terminal a to terminal A, but in the present invention, immediately after leaving terminal a, Since almost no discharge occurs, there is also the advantage that the distance from terminal a to terminal A is not required to be exact.

[Brief explanation of the drawing]

Figures 1 and 3 are circuit diagrams showing conventional touch response circuits, Figures 2 and 4 are diagrams showing the discharge characteristics of the capacitors in Figures 1 and 3, respectively, and Figure 5 is a diagram showing the present invention. 6 is a diagram showing the discharge characteristics of the capacitor in FIG. 5, and FIG. 7 is a specific circuit diagram for realizing the circuit of FIG. 5. Co, C1, C2... Capacitor, R1, R2
゜R3, R4, R5...Resistance, KSW...
・・Press key switch, S・・・・Switch, Trl, Tr
2...Transistor.

Claims (1)

[Claims] 1. A touch response circuit in which a resistor circuit is connected in parallel to a capacitor, and the voltage charged in the capacitor is discharged through the resistor circuit as time passes after the key press switch is activated. Immediately after the key press switch is activated, the charging voltage of the capacitor is discharged through the first resistor circuit having a high resistance value, and the voltage of the capacitor is set to the first resistor circuit.
A touch response circuit characterized in that after discharging to a predetermined level through the resistor circuit, the touch response circuit is also discharged through a second resistor circuit having a resistance value lower than the resistance value of the first resistor circuit.