JP2003262597A - Power-saving method in variable resistance sensor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a simple and low-cost variable resistance sensor system and to manufacture a circuit to be operated at a low power consumption. <P>SOLUTION: When a resistance value detected by a sensor is used as a resister of an oscillation circuit by a CMOS, the resistance value has an infinite or large value when the sensor does not perform a detecting operation, the oscillation circuit is not operated or it is oscillated at a low frequency, and its power consumption is zero or in a very small amount. Since a switch is not used, the sensor is low-cost. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor system using a sensor for detecting a change in resistance value, and provides a method for reducing power consumption with a simple circuit structure at low cost. It is a thing.

The present invention relates to an apparatus mainly composed of an electric circuit having a sensor of a type for detecting a change in resistance value and a system for converting the sensor into something which can be recognized by humans by a display or the like. It provides a method in which the power consumption of the circuit is extremely low or zero when the detection operation is not performed in the sensor by starting the operation of the device in conjunction with the change in the resistance value of the sensor. is there.

[Prior art]

Conventionally, in an electronic device, an electric circuit is usually operated by turning on some kind of switch by a human hand, and even if there is a switch to which a sensor or the like is applied, a circuit function in a state where a power source is turned on is provided. One of them is to judge the level of the sensor and operate the switch, and the circuit consumes power in the standby state even when the switch by the sensor is not working. It was either incomplete or incomplete.

[Problems to be Solved by the Invention]

In the present invention, it is intended to reduce the power consumption of the circuit without providing a switch and to manufacture a low-cost product.

[Means for Solving the Problems]

In the present invention, the power consumption is only in the moment when the state of high and low output levels is switched,
The oscillation circuit is formed with the element of resistance and the capacity using the CMOS element which is originally characterized by low power consumption. In the oscillation circuit, a switch circuit is formed in series with a part of the resistance and the capacitance that define the oscillation condition. If the resistance value of the switch circuit is infinite or relatively large, the oscillation circuit Does not operate or operates at an extremely long cycle, resulting in zero or very low power consumption. As the resistance value of this switch becomes relatively low, the oscillator circuit operates and the sensor system circuit operates. It works. According to this method, if the sensor is a resistance change type, it is possible to configure the switch part by utilizing the change in the resistance value, and it is necessary for a person to manually configure the switch to be directly operated. Not only that, when the sensor system is not operating, the circuit operation is automatically stopped or the frequency is lowered to a relatively low level, so that unnecessary power consumption due to forgetting to switch off can be suppressed and there is no need to provide a special switch. Therefore, it also has the feature that the product can be manufactured at a low price.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described with reference to FIG. 1, which is a circuit of a so-called moisture sensor for measuring and displaying moisture of soil. Here, the portion surrounded by 1 is the oscillation circuit portion, the portion 2 is the electrode portion, and the portion 3 is the level determination and liquid crystal display portion. Further, for convenience, the circuit portions indicated by I and II are symbols used to show that they are portions having either a high potential or a low potential, which are alternating currents of a substantially rectangular wave and opposite in phase to each other.

The moisture sensor is composed of an oscillating circuit section indicated by 1 in FIG. 1, a sensor head section indicated by 2 and a level judgment and display section indicated by 3 in FIG. Here, the elements used in the oscillation section and the determination section are not only resistors and capacitors but also CMOS inverter elements, and normally six elements are formed in one IC package. Here, an example is shown in which all functions are realized with 6 inverters by using a one-package IC, but the number of inverters is not limited to 6 and the number of inverters is made more stable to make the oscillation circuit more stable. Using more inverters by increasing or increasing the number of level settings for level determination is advantageous in terms of realizing a higher function. Although not shown here, a battery having a voltage of 3 V or higher is usually connected to the power supply terminal of the CMOS-IC.

The portion 2 is an electrode portion which is inserted into the soil to detect a change in the resistance value depending on the degree of water content of the soil. When the portion is not inserted into the soil, insulation is provided between the electrodes. In this state, when it is inserted into the soil, a relatively low resistance value is detected through the soil in contact with this electrode.

The third part is a level judgment and display part, which will be described in detail in the embodiment, but the resistance value of the soil detected in the second part is compared with the fixed resistance value, and the input of the inverter is compared. The output is used to drive a display device such as a liquid crystal display.

【Example】

An embodiment according to the present invention will be described. The example described here relates to a moisture meter, but here, when a direct current is applied when measuring the resistance value of soil, an oxide film is formed on one electrode surface by an electrolytic action. The resistance value changes irreversibly, and there is a problem that the resistance value increases because it is superimposed on the resistance value to be detected, and alternating current should be used, and in the display element such as liquid crystal Since a so-called polarization effect is caused when DC is driven and the liquid crystal is deteriorated, an AC should be applied to this as well.Therefore, use an oscillation circuit to apply the AC generated in the oscillation circuit to these electrode parts and liquid crystal part. I have to.

For this reason, in a system which is generally AC driven and uses a resistance change type sensor or a liquid crystal, a switch is operated by operating, stopping or lowering the frequency of the oscillation circuit in the same manner. It can be easily inferred from this example that a power-saving circuit can be formed by switching ON and OFF. As a resistance change type sensor, there are many ones whose resistance value changes logarithmically like a semiconductor as represented by a thermistor and a gas sensor. In such a sensor, it is known that the resistance value appears in several orders of magnitude when operating and when not operating. Therefore, it is easy to discriminate between such operation and non-operation, and the oscillation frequency is large. It is easy to catch as a change. It is known that the resistance value of a moisture meter is infinite when it is not operating, and it is in the range of several hundreds of kilohms to 1 kiloohm when operating, although it is slightly different depending on the electrode spacing and the like.

Here, the part of the circuit 1 in FIG. 1 is an oscillating circuit composed of two CMOS inverters and two resistance values and one capacitor, and one resistance part of the circuit is 2
A pair of electrodes in the electrode part of is connected in series, this electrode part is always open circuit, therefore the resistance of the circuit part connected to it is infinite, oscillation does not occur, therefore in CMOS circuit There is no power consumption, and no current flows in other circuit parts as described later, so there is no power consumption. In the circuit 1 portion of FIG. 1,
The electrode is placed in series with one of the resistors in the middle,
It can also be in series with the other resistor.
However, in this oscillator circuit, the resistance value of the middle part is usually set lower than that of the other resistor, and when the electrodes are connected to the other resistor in series, the input impedance of the inverter circuit is also high. The operation starts from the high resistance level of the electrode unit, which is on the order of several megohms. Since such a resistance value is generated even with a small amount of dirt, the operation may be relatively unstable.

FIG. 2 is an enlarged view of the electrode portion.
The portion used for the switch function is pair 1 and the portion used for the sensor function is pair 2 so that the electrode interval of pair 1 is narrow. When a comparatively low resistance value is generated in the electrode part of this pair 1 due to contact with soil, a combined resistance value is generated by the electrode part and the fixed resistance part of the circuit, and oscillation at a frequency according to the circuit constant is generated. Occurs and an alternating current is generated.
At this time, the resistance value of the soil due to this electrode portion is lower than the fixed resistance value in series, and it is desirable to reduce the fluctuation of the oscillation circuit constant due to the resistance value. It is desirable that the electrode interval in the portion of this pair 1 is as narrow as possible and has low resistance. Practically, the fixed resistance value of the intermediate part of the circuit connected in series with the electrode is several hundred kilohms to 1 megohm, and the other has a resistance value in the order of several megohms, and the capacity is about 0.05 microfarad. The oscillation frequency at this time is 50 to 10
The level was 0 Hz. The resistance value of the pair 1 of the electrode part may reach several hundred kilohms when the soil is completely dry, but it is lower by one digit or more during normal use, and the frequency fluctuation is not a practical problem. Further, in this case, it is possible to regard it as one level of determination by defining that the non-operating state is too dry. In addition to this simplest circuit, various circuits such as a method using three inverters are known for the oscillation circuit, but in each case there is a resistor as one element that determines the oscillation constant. ON / OFF operation is possible by the resistance control method.

As shown in FIG. 2, the electrode portion is composed of three electrodes, one of which is a common electrode, the pair 1 is relatively close to each other, and the resistance is as low as possible. The pair 2 is connected in series to the resistance of the circuit, and the pair 2 has a relatively large interval so that it is easy to recognize the change in the resistance value of the soil. Specifically, the electrode size is 1 mm x 2
The distance between the pair 1 was set to 0 mm, the distance between the pair 1 was set to 0.5 mm, and the distance between the pair 2 was set to about 3 mm. Since this resistance value differs depending on the type of soil and the like, it should be experimentally determined depending on the individual case.

The part 3 in FIG. 1 is the level judgment and liquid crystal drive and display part. Since it is not the main part of this patent, the operation will be briefly described. When the second pair of electrode parts 2 is infinite, one end of the resistor string is in an open state in this electrode part and no current flows, so the power consumption is zero.
Further, the voltage on the input side of the inverters of the four determination circuits is the same as the level of I even if it passes through the resistance, and the output is inverted and therefore the same as the level of II. When a resistance is generated in the pair 2 of the electrode parts and the voltage value of the input terminal of the first inverter from the II side of the inverter is less than 50% in the voltage between I and II, that is, when it is closer to the II side, the output Is inverted,
It is the opposite phase to II and the same phase as I, which means that the liquid crystal on the most II side is turned on, and when the second input voltage falls below 50%, the second one is turned on and the resistance value becomes sequential. The liquid crystal will light up accordingly. That is, as the soil contains water and the resistance value becomes smaller, the input voltage of the inverter sequentially falls below 50%, and the level corresponding to the resistance value level appears as a liquid crystal display. The characteristic of the CMOS-IC element used here is that the output level is inverted at the boundary whether the input voltage level exceeds or does not exceed 50% of the power supply voltage. In the inverter,
For example, if the power supply voltage applied to the IC is 3V, the output is 3V and the input level is 1.
If it exceeds 5V, the output will be 0V. In this circuit, the voltage applied to the liquid crystal is a substantially rectangular wave AC generated by the inverter, but the same applies to the judgment circuit.
When alternating current is applied from the portions I and II and the inverter is operated, the liquid crystal is always driven so as to have opposite phases, so that the liquid crystal always keeps the lighting state. Further, the liquid crystal operates by an electric field, and an impedance due to a capacitive component exists in an AC operation, but a current does not flow in a DC current and power consumption does not occur. That is, when the oscillation circuit is not operating, power consumption in the liquid crystal It is zero.

In the present embodiment, the electrodes and circuits are formed on a flat plate by screen printing, and the electrode structure to be inserted into the soil is also printed on one end of the elongated substrate so that the substrate itself is inserted into the soil. did. As a result, no special external mounting structure was used for the electrode structure.The electrode was printed with silver paste on the edge of the substrate, and the resistive material containing carbon was printed on it to protect and further expose the part. Other than that, a conformal coat was printed. In the case of a metal or the like, the electrode is easily corroded or oxidized to be deteriorated, and thus a stable carbon-containing printed resistance paste is used for protection. Carbon resistance paste has a resistance value,
It is a resistance in the thickness direction due to printing, and even if the resistivity of the material is high, the actual resistance value expressed by multiplying the thickness and dividing by the area is a low value that is practically no problem from the fact that the thickness is 10 microns or less. is there. Known methods are used for other circuit configurations.

【The invention's effect】

According to the present invention, since the operation of the circuit can be operated, stopped, or lowered in frequency without providing a switch for turning the circuit on and off, a simple and low-priced circuit configuration is possible. When the sensor system is not used, the operation is automatically stopped or the frequency is lowered, so there is an effect that a power saving circuit can be configured without wasting power during the time other than the net usage time.

[Brief description of drawings]

[Figure 1] Overall view of the circuit

FIG. 2 is an explanatory diagram of electrodes

[Explanation of symbols]

1. Oscillation circuit section 2. Electrode part 3. Level judgment and liquid crystal display A code indicating one phase and voltage of the I circuit II Sign indicating the other phase and voltage opposite to I

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Morimitsu Wakabayashi             132 Haneshin, Fuchu-cho, Neguro-gun, Toyama Prefecture (72) Inventor Masahiro Kadosaki             180 Shinmachi, Nuno, Toyama F-term (reference) 2G060 AA14 AD02 AE16 AF07 AG13                       EB04 HA09 HC09 KA10

Claims (3)

[Claims] 1. A sensor device of the type that detects a change in resistance value, wherein the oscillation circuit is operated by utilizing the change in resistance value to be detected, so that the oscillation circuit does not operate during a time other than the detection operation, or A power saving method characterized in that power consumption is reduced due to relatively low frequency oscillation. 2. The change in the resistance value according to claim 1 is such that the resistance value is infinite or a relatively high resistance value when the detection operation is not performed, and therefore the oscillation circuit does not operate or has a relatively low frequency. It is an oscillation, and the resistance value at the time of the detection operation is a relatively low resistance value, so that it oscillates at a relatively high frequency. 3. The CMOS according to claim 1, wherein the oscillator circuit consumes almost no power except when the oscillator circuit is operating.
-Characterized by using elements such as IC.