JPS636883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a reference voltage (hereinafter referred to as V _REF ) of an A/D converter of a microcomputer (hereinafter referred to as a microcomputer) that has a built-in so-called analog/digital converter (hereinafter referred to as an A/D converter).
The present invention also relates to a microcomputer control circuit that controls the supply of drive power to an analog input circuit.

Figure 1 shows a conventional device that converts an analog temperature signal detected by an NTC thermistor into a digital temperature signal using an A/D converter built into a microcomputer (hereinafter referred to as microcomputer). The conventional device will be explained with reference to FIG. FIG. 1 shows a conventional circuit of this type, in which 1 is a DC power source obtained by rectifying an AC power source, 12 is a microcomputer equipped with an A/D converter connected to the power source 1, and 13 is a DC power source obtained by rectifying an AC power source. An output circuit driven by n outputs of the microcomputer 12, 11 is a resistor, 9 is a constant voltage diode, and 10 is a noise removal capacitor. The reference voltage that is the conversion reference for the A/D converter built into the device is input to the V _REF terminal, which corresponds to the input terminal. Further, 3 is a resistor, 2 is a constant voltage diode, and 4 is a noise removal capacitor, which together with the constant voltage diode 2 and resistor 3 constitute a constant voltage power supply circuit of the analog input circuit. 5 and 7 are resistors connected in series, and the series circuit of these resistors 5 and 7 is connected in parallel to the voltage diode 2. Reference numeral 6 denotes an NTC thermistor connected in parallel to the resistor 7, which corresponds to a temperature detection sensor that detects the room temperature when used, for example, to control the room temperature of a room air conditioner. 8 is a noise removal capacitor connected in parallel to the resistor 7, and the connection point between the NTC thermistor 6 and the resistor 5 is connected to the K input terminal of the microcomputer 12 into which an analog temperature signal is input.

In the above configuration, if the values of resistor 5 and resistor 7 are appropriately selected taking into consideration the resistance value and temperature coefficient of NTC thermistor 6, which corresponds to the indoor temperature sensor, the result as shown in Figure 2 is obtained. An almost linear relationship can be obtained between the ambient temperature of the thermistor, for example, room temperature, and the voltage across the thermistor. Furthermore, if the voltage of the constant voltage diode 2, which determines the drive voltage value of the analog input circuit, is appropriately determined with respect to the voltage of the constant voltage diode 9, which provides the reference voltage V _REF of the A/D converter built into the microcomputer 12, From the linear relationship between the thermistor and its ambient temperature in Figure 2, the microcomputer 12 calculates the absolute value of the change in temperature for each bit of change in the A/D converter, such as IC/bit. It can be a value that is easy to process. That is, for example, if the output "00011" of the A/D converter corresponds to an indoor temperature of 10°C, the output will be increased by 1 bit to "00100".
When the indoor temperature is 11°C, the output "00101" which is further increased by 1 bit can correspond to the indoor temperature of 12°C.

With this configuration, the DC power supply 1
The microcomputer 12 was able to perform arithmetic processing of analog inputs stably against fluctuations in the data.

However, this configuration has a constant voltage diode 9 for providing a reference voltage and a constant voltage diode 2 for determining the voltage of the analog input circuit.
and two constant voltage diodes are required, and in order to make the change in temperature relative to the change in 1 bit of the A/D converter into a value that can be easily processed by the microcontroller 12, such as IC/bit. In this case, it was necessary to select an appropriate constant voltage diode 2 for each variation in the voltage of the constant voltage diode 9. This not only has the drawback of increasing the number of work steps needed to mass produce this circuit, leading to an increase in costs, but also has the drawback of hindering maintenance and serviceability after it goes on the market. The present invention has been made in order to solve the above-mentioned drawbacks, and is not affected by fluctuations in the DC power supply, and moreover, it is not affected by changes in the analog input per bit of the A/D converter, e.g. This provides a circuit that can arbitrarily set the degree of temperature change in degrees Celsius.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.
FIG. 3 is a circuit diagram showing an embodiment of the present invention,
Hereinafter, the same reference numerals as in FIG. 1 indicate the same or corresponding parts. In FIG. 3, 16, 17, and 18 are resistors connected in series, and the series circuit of the resistors 16, 17, and 18 is connected to the power source 1. 14 is resistance 16
Noise removal capacitor connected in parallel with 1
Reference numeral 5 denotes a noise removal capacitor connected between the connection point of the resistor 17 and the resistor 18 and the positive terminal of the power supply 1. 19 and 20 are operational amplifiers (hereinafter referred to as operational amplifiers); the non-inverting input terminal of the operational amplifier 19 is connected to the connection point between the resistors 16 and 17, and the inverting input terminal is connected to the V _REF terminal of the microcomputer 12. connected to the output terminal. Also,
The operational amplifier 20 has the same configuration as the operational amplifier 19, and its non-inverting input terminals are connected to the resistors 17 and 18.
The output terminal is also connected to the resistor 5.

Here, the configuration of the operational amplifier 19 and the operational amplifier 20 is what is called a voltage follower, and it is known that the input impedance thereof is extremely large and the output impedance is small.
That is, the voltage at the output terminal of the operational amplifier 19 is
6 and the voltage at the connection point of resistor 17, and
The voltage at the output terminal of the operational amplifier 20 is equal to the voltage at the connection point between the resistors 17 and 18, and its output impedance is small. In such a configuration, if the values of resistors 16, 17, and 18 are appropriately selected, the temperature change per 1 bit of the A/D converter can be set to, for example, 1°C/bit. In addition, by making at least one of the resistors 16 and 17 a variable resistor, it can be set arbitrarily. Furthermore, with respect to voltage fluctuations of the power source 1, the voltage at the connection point between the resistors 16 and 17 and the voltage at the connection point between the resistors 17 and 18 also change at the same rate. That is, since the voltage at the V _REF terminal and the voltage at the K input terminal of the microcomputer 12 change at the same rate, the calculation results of the A/D converter of the microcomputer 12 are not affected at all.

As described above, according to the present invention, it is possible to arbitrarily set the amount of change in analog input per 1 bit of the A/D converter built in the microcomputer 12, and it is not affected by voltage fluctuations of the power supply 1. It has the advantage of being able to provide circuits.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional embodiment, FIG. 2 is a characteristic diagram for explaining the operation of FIG. 1, and FIG. 3 is a circuit diagram showing a specific embodiment of the present invention. In the figure, the same symbols indicate the same or equivalent parts, 1 is a DC power supply, 2 and 9 are constant voltage diodes,
5, 7, 16, 17, and 18 are resistors, 6 is an NTC thermistor, 8, 14, and 15 are capacitors, 12 is a microcomputer with a built-in A/D converter, 13 is an output circuit, and 19 and 20 are operational amplifiers.

Claims (1)

[Claims] 1 DC power supply, A/D connected to the DC power supply
In a device comprising a microcomputer with a built-in converter, an analog input circuit connected to the microcomputer, and an output circuit of the microcomputer, a series circuit consisting of two or more resistors is connected to the DC power supply, The voltages obtained by impedance conversion of the different voltages from the connection points of the resistors using operational amplifiers are applied to the A/
A microcomputer control circuit characterized in that the reference voltage of a D converter and the drive voltage of an analog input circuit are used.