JPH0511792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a sensor circuit that detects the states of a plurality of sensors with less wiring.

<Summary of the Invention> This invention sets the amount of current flowing through multiple sensors that are switched on and off to a predetermined value, and when detecting the state of each sensor, calculates the sum of the currents flowing through each sensor. The state of each sensor is detected by detecting the voltage as a voltage and performing A/D conversion.

<Background of the Invention> Conventionally, a circuit as shown in FIG. 7 has been used as a sensor circuit for detecting the on/off states of a plurality of sensors provided in a certain device. In the figure, SW1 to SW8 are sensors, to which strobe signals S1 and S2 are supplied,
The return signals are input as I0 to I3.
This method of detecting the on/off state of a sensor based on the relationship between a strobe signal and an input signal requires at least one signal line for each sensor, and an additional line for supplying the strobe signal. signal lines are required.

Even with this method of detecting the state of each sensor in a time-sharing manner, a large number of signal lines are required, and there are problems in that thick cables must be wired. In addition, a detection circuit that detects the state of each sensor requires many parts depending on the number of sensors, and in the case of a device that requires a large number of sensors, this is also a factor in increasing costs.

Therefore, for example, as shown in Figure 3, the sensor
Resistors Ra to Rd are connected in series to each of SW1 to SW4, and a voltage dividing resistor Ri is connected to detect the sum of currents flowing through these. Now, suppose Ra, Rb,
Assuming that the resistance value of Ri is small compared to Rc and Rd and its influence can be ignored, the current flowing in each branch is Ia = Vc / Ra, Ib = Vc / Rb, Ic = Vc / Rc, Id
=Vc/Rd.

Therefore, Vin=RiVc(A/Ra+B/Rb+C/Rc+D/
Rd).

Here, A, B, C, D are sensors SW1, SW
2, represents 1 when SW3 and SW4 are on, and represents 0 when off.

Now, if the relationship is Ra:Rb:Rc:Rd=1:2:4:8, the above equation becomes Vin=VcRi/Rd (8A+4B+2C+D).

As is clear from the above, the on/off state of each sensor corresponds to each bit of a 4-bit binary number. However, in reality, the resistance Ri cannot take a negligibly small value, and as shown in Figure 4, the A/R depends on the on/off state of each sensor.
The input voltage Vin to the D converter is a curve. As a result, the potential difference depending on each state of the sensor is no longer constant, and a region with a small voltage difference occurs.

By the way, A/D converters have a certain range of input voltage, which is generally the A/D converter.
Determined by the converter reference voltage Vref. As shown in Figure 5, considering the case where the constant voltage source Vc is used as the reference voltage of the A/D converter, the resistance Ri is smaller than Ra, Rb, Rc, and Rd as shown in Figure 6. The more the input voltage curve becomes linear, but the more the A/D
The converter can only be used at the lower level of the input range. Conversely, increasing the resistance Ri widens the usable input range, but the input voltage curve deviates significantly from a straight line, resulting in the disadvantage that the voltage difference between each state becomes small in the high input voltage region. Current − using an operational amplifier
If a voltage conversion circuit is constructed, the above-mentioned disadvantages can be solved, but there is a drawback that the circuit becomes complicated.

<Objective of the invention> An object of the invention is to extremely reduce the number of signal lines between a plurality of sensors and a detection circuit that detects the on/off state of each sensor, and to configure the sensor circuit with a simple circuit. It is in.

<Configuration and Effects of the Invention> The present invention connects a plurality of sensors that switch on and off in parallel, connects a resistor in series with each sensor, and sets the magnitude of each resistor to a different power of two. Further, an A/D converter is provided to A/D convert the sum of the currents flowing through each sensor,
The converter detects the state of each sensor by A/D converting the voltage obtained by a low resistance that constitutes a voltage dividing circuit together with a resistor connected in series with each of the sensors. It is characterized by

With the above configuration, the sensor circuit can be easily configured with only the resistors, voltage dividing resistors, and A/D converters connected in series to each sensor.
Moreover, the amount of current flowing through each sensor is a value proportional to a different power of 2. Therefore, the relationship between the input of the A/D converter and the converted value becomes linear.
Furthermore, since it can be used over the full scale of the input voltage of the A/D converter, the resolution of the A/D converter can be increased.

<Embodiment> FIG. 1 shows a sensor circuit which is an embodiment of the present invention.

SW1, SW2, SW3, and SW4 are each sensors, and resistors Ra, Rb, Rc, and Rd are connected in series with each sensor.
are connected, all of these series circuits are connected in parallel, a voltage dividing resistor Ri is connected to one electrode, and the voltage Vin obtained by this voltage dividing resistor is
is connected to the input of the A/D converter. A constant voltage source Vc is connected to the circuit consisting of the resistor and sensor, and the current flowing through the resistor Ri is determined depending on the on/off state of each sensor. Resistance Ra, Rb,
The ratio of the resistance values of Rc and Rd is 1:2:4:8 as in the case shown in Figure 3, but the reference voltage Verf of the A/D converter is four times the constant voltage source Vc. set to the value. Also, the voltage dividing resistance Ri is (3/20)
It is set in relation to Ra. In this way, A/
By setting the reference voltage Verf of the D converter higher than Vc, which is the power supply voltage of the sensor, the value of the voltage dividing resistor can be set small. According to the above conditions, the relationship between the input voltage Vin of the A/D converter depending on the state of each sensor becomes approximately linear as shown in FIG.

In this way, the value of the voltage dividing resistor is set to a lower resistance value that is less than a fraction of the lowest resistance among the resistors connected in series with each sensor, and the maximum value obtained by dividing the voltage by the voltage dividing resistor is set. The reference voltage is set as the full-scale voltage of the input voltage of the A/D converter.
By setting Verf, the resolution of A/D conversion can be increased with a simple circuit without using an operational amplifier or the like, and the states of a large number of sensors can be detected without error.

[Brief explanation of the drawing]

FIG. 1 shows a sensor circuit which is an embodiment of the present invention.
Figure 2 is a diagram showing the relationship between the state of each sensor in the same sensor circuit and the input voltage of the A/D converter;
FIG. 4 is a circuit diagram showing the operating principle behind this invention, FIG. 4 is a diagram showing its operating characteristics, and FIG. 5 is an example of a sensor circuit for explaining the background of this invention.
FIG. 6 is a diagram showing its operating characteristics, and FIG. 7 is a diagram showing an example of a conventional sensor circuit. 1...A/D converter, SW1, SW2, SW3,
SW4...sensor, Ra, Rb, Rc, Rd...resistance,
Ri...Divisional voltage resistance.

Claims (1)

[Claims] 1 Connecting a resistor having a resistance value proportional to a power of 2 and having a different size to each of the plurality of sensors that are switched on and off,
A parallel circuit formed by connecting these plurality of series circuits in parallel, and a parallel circuit having a resistance value lower than a fraction of the lowest resistance among the plurality of resistances, and a current flowing through the parallel circuit. A voltage dividing resistor is connected in series to extract the sum of the current as a voltage, and an A/D converter is provided to convert the maximum voltage obtained by dividing the voltage by the voltage dividing resistor into a full-scale voltage. A sensor circuit characterized in that the state of each of the sensors is detected by the output of an A/D converter.