JPH08274611A - Field equipment touch key - Google Patents

Abstract

PURPOSE: To provide a touch switch which has a stable operation despite the change of its ambient environment. CONSTITUTION: When a transistor TR 3 is driven by a drive circuit 2, the current outputted from a control circuit 10 where a constant current flows despite the change of its ambient temperature is supplied to a light emitting diode 1. In such a constitution, the quantity of light emitted from the diode 1 is kept at a constant level. Furthermore, the signal detected by a light receiving TR 5 is also kept at a constant level. Thus a stable operation is secured for a touch switch.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field device touch key which is attached to a field device and which detects a touch of a reflector such as a finger to generate an output signal.

[0002]

2. Description of the Related Art Generally, a touch key does not require a mechanical operation part and can improve confidentiality.
Widely used in various devices. This is to generate infrared light with a light emitting element such as a light emitting diode, irradiate the transparent body with the infrared light, and touch a finger on the outside of the transparent body. Since it is reflected and the reflected light reaches the light receiving circuit through the transparent body again, it is detected there to detect the operation of the key.

When infrared light is constantly generated, the light receiving circuit cannot distinguish whether the detected infrared light is regular reflected light or ambient light, so the infrared light is pulsed at a predetermined frequency. It is generated by a signal, and the detection circuit compares the pulsed signal with the reflected light, and generates a normal detection signal only when the comparison is successful.

[0004]

When such a switch is used for indoor equipment, there is no problem because the environmental conditions are constant, but when it is used for field equipment, the field equipment is placed under various environments. Therefore, the amount of infrared light may change or the detection sensitivity may change depending on environmental conditions. For this reason, for example, in the daytime, direct sunlight hits and the response of the touch key is good, but at night, the response may be slow due to cooling. The present invention has been made in view of such a situation,
It is designed to operate stably even if the surrounding environment changes.

[0005]

In order to solve such a problem, the present invention provides a drive circuit for sending a pulsed drive signal having a predetermined frequency, and emitting infrared light modulated by the drive signal to a transparent body. Light emitting circuit, a light receiving circuit that receives the infrared light reflected by the reflector when the reflector is located outside the transparent body, and a constant amount of infrared light is controlled according to the temperature near the light emitting circuit. And a control circuit for

[0006]

A current flows through the light emitting circuit in response to a pulsed drive signal having a predetermined frequency, and the current is controlled by the control circuit so as to have a constant value regardless of the ambient temperature. The amount of light becomes constant.

[0007]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which a light emitting diode 1 is generated by a drive circuit 2.
Pulsed infrared light is generated by being on / off controlled by the transistor 3 driven by a pulsed driving signal having a predetermined frequency shown in (a). The infrared light is emitted to the transparent body 4 provided on the panel of the field device. This infrared light almost passes through the transparent body 4, but a part of it is reflected by the transparent body 4 and detected by the light receiving transistor 5, and a detection signal of the portion described as having no reflector in FIG. 2B is generated. When the outside of the transparent body 4 is touched with the reflector 11, in this example, the infrared light passing through the transparent body 4 is reflected by the reflector 11 and again supplied to the light receiving transistor 5 through the transparent body 4. The light receiving transistor 5 is detected as a signal of the amplitude of the portion described as having reflected light in FIG.

The detected infrared light is amplified by an amplifier circuit 6 composed of an amplifier 6a and a resistor 6b, and a peak value is detected by a peak detector 8 via a bandpass filter 7. At this time, even if noise is mixed in as shown in FIG.
With the frequency shown in (a), noise can be removed because it is a very high frequency component.

Therefore, the signal that has passed through the bandpass filter 7 is supplied to the peak value detector 8 as a signal from which noise has been removed, as shown in FIG.
Holds the peak value and converts the pulse signal into a direct current as shown in FIG. The signal is supplied to the comparator 9, and only the portion having a predetermined level or higher is detected.
It is output as a key input signal as shown in.

Since the current flowing through the light emitting diode 1 changes depending on the ambient temperature and the amount of infrared light generated changes, a current is supplied through the control circuit 10 for keeping the amount of infrared light constant, and the ambient temperature changes. Even so, the amount of infrared light generated by the light emitting diode 1 is not changed. In order to prevent the current flowing through the light emitting diode 1 from changing even when the ambient temperature changes, a temperature detecting element whose electrical characteristics change according to the ambient temperature, in this example, a thermistor 10a whose resistance value changes depending on the ambient temperature, is used. Resistance 10b
The control circuit 10 is configured by connecting the
The thermistor 10 a is provided near the light emitting diode 1. Then, by supplying a current to the light emitting diode 1 from the connection point of the thermistor 10a and the resistor 10b, the current flowing through the light emitting diode 1 is made constant. In this way, if the current flowing through the light emitting diode 1 does not change depending on the ambient temperature, the amount of infrared light emitted from the light emitting diode 1 does not change.

FIG. 3 is a circuit diagram showing another embodiment. In addition to the function shown in FIG. 1, the amplifier circuit 6 is also composed of an amplifier 6a, a thermistor 6b and a resistor 6c and temperature-compensated. If the amount of light emitted from the light emitting diode 1 is kept constant and the amplification degree of the amplifier circuit 6 does not change with temperature, stable operation can be expected even if the change in the surrounding environment becomes larger.

[0012]

EFFECTS OF THE INVENTION A current flows through a light emitting circuit in response to a pulsed drive signal having a predetermined frequency, and the current is controlled by a control circuit so as to have a constant value regardless of ambient temperature. Since the amount of light is constant, the level of the detected signal is constant regardless of the ambient temperature, which is normal in the daytime when it is exposed to direct sunlight, but it becomes nighttime and the ambient temperature When the value decreases, an accident that does not operate normally does not occur. In particular, when it is attached to the surface of a field device, the environment is likely to change greatly, so that it has a particularly remarkable improvement effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a waveform chart of each part of the circuit of FIG.

FIG. 3 is a circuit diagram showing a configuration of another embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light emitting diode, 2 ... Drive circuit, 3 ... Transistor, 4 ... Transparent body, 5 ... Light receiving transistor, 6 ... Amplifying circuit, 6a ... Amplifier, 7 ... Band pass filter, 8 ... Peak detector, 9 ... Comparator, 10 … Control circuit, 11…
Reflector.

Claims (1)

[Claims] 1. A drive circuit for transmitting a pulsed drive signal having a predetermined frequency, a light emitting circuit for emitting infrared light modulated by the drive signal to a transparent body, and a reflector positioned outside the transparent body. A touch for a field device including a light receiving circuit that receives the infrared light reflected by the reflector and a control circuit that constantly controls the light amount of the infrared light according to the temperature near the light emitting circuit. Key.