JPH0511861B2 - - 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 a plurality of sensors that are switched on and off to a predetermined value, and converts the sum of the currents flowing through each sensor into an A/D converter. Therefore, the state of each sensor is detected, and in particular, it is configured to operate with a single polarity power source.

<Background of the Invention> Conventionally, a circuit as shown in FIG. 3 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.
In this method of detecting the on/off state of a sensor based on the relationship between a strobe signal and an input signal, at least one signal line is required for each sensor, and the strobe signal is also supplied. A signal line is required for this purpose.

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 4, the sensor
A current ia with a predetermined value for each of SWa to SWd
The on/off state of each sensor can be detected by setting the circuit so that ~id flows and using a current detection circuit to detect the sum of the currents flowing through each of these sensors. Conventionally, the fifth circuit has been used as a circuit for detecting the states of multiple sensors using this method.
Something like the one shown in the figure is being considered. In the same figure, SWa to SWd are sensors, each with a resistance Ra
A constant voltage Vr is applied to a circuit in which ~Rd are connected in series, the sum of the currents flowing through each sensor is converted to a voltage by the current/voltage conversion circuit 2, and the voltage is converted to a voltage by the A/D converter 1. and then converted into digital code.

In such a sensor circuit, the current/voltage conversion circuit 2 is constituted by an inverting feedback circuit using an operational amplifier. Therefore, when the voltage Vr applied to each sensor is a positive voltage, the output of the current/voltage conversion circuit has negative polarity, and the A/D converter 1 must operate with negative voltage input. . Conversely, in order to use an A/D converter that operates with positive voltage input, the voltage Vr must have negative polarity. In either case, conventional sensor circuits require power supplies with both positive and negative polarities, which has the disadvantage of complicating the power supply circuit.

<Objective of the Invention> An object of the invention is to minimize the number of signal lines between a plurality of sensors and a detection circuit that detects the on/off state of each sensor, to use a single polarity power supply, and to create a simple circuit. The purpose of this is to configure a sensor circuit.

<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 2. further provided with a current/voltage conversion circuit that converts the sum of the currents flowing through each sensor into a voltage, and an A/D converter that converts the output voltage of the current/voltage conversion circuit from A/D,
The sensor circuit detects the state of each sensor based on the output of this A/D converter, and the current/voltage conversion circuit is configured with an inverting feedback circuit using an operational amplifier, and a reference voltage input to the operational amplifier is provided. A reference voltage that is equal to the maximum input voltage of the A/D converter and equal to a voltage that changes the output voltage of the current/voltage conversion circuit in the range from 0 potential to the reference voltage of the operational amplifier is applied to the terminal. shall be.

With the above configuration, the output range of the inverting feedback circuit is shifted by the voltage applied to the reference voltage input terminal of the operational amplifier constituting the inverting feedback circuit. For this reason,
The output voltage of the current/voltage conversion circuit ranges from 0 to the voltage applied to the reference voltage input terminal of the operational amplifier, which corresponds to the input voltage range of the A/D converter. In this way, the current/voltage conversion circuit and the A/
Both D converters can be operated with a single polarity power supply, simplifying the power supply circuit.

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

SWa to SWd are sensors, and resistors Ra to Rd are connected in series to each sensor, and all of these series circuits are connected in parallel, and one electrode is connected to a power supply Vr that generates a constant voltage via a cable L1. connected in common. The other electrode is cable L
2, they are commonly connected to the current/voltage conversion circuit 2. This current/voltage conversion circuit 2 is composed of an operational amplifier OP, a resistor Rf, and a reference voltage source Vref, and the output voltage V is expressed as V=Vref−Rf·i.

Here, i is the current flowing through the cable L2 and is expressed by the following equation.

i=((a/Ra)+(b/Rb)+(c/Rc)+(d/
Rd))Vr Therefore, the output voltage V of the current/voltage conversion circuit
is expressed as follows.

V=Vref−Rf((a/Ra)+(b/Rb)+(c/
Rc)+(d/Rd))・Vr However, in the above two equations, a, b, c, d
is 1 when the sensors SWa, SWb, SWc, and SWd are in the on state, and 0 when the sensors are in the off state.

Here, if the ratio of resistance values is Ra:Rb:Rc:Rd=1:2:4:8, then V=Vref−(Rf/Ra)(a+(b/2)+(c/
4) + (d/8)) Vr = Vref - (8a + 4b + 2c +
d)・RfVr/8Ra Here, the value of the reference voltage Vref of the operational amplifier is
By determining the values of the feedback resistor Rf, the constant voltage Vr applied to each sensor via the resistor, and the resistor Ra so that the relationship Vref=15RfVr/8Ra is established, the output voltage V of the operational amplifier can be set for each sensor. The value ranges from 0 to Vref depending on the on/off state.

The possible range of the output voltage V of this operational amplifier corresponds to the full scale of the input voltage of the A/D converter. Therefore, 4-bit codes D1 to D4 are obtained depending on the on/off state of each sensor.

Figure 2 shows the on/off status of each sensor and the A/D
It is a figure showing the relationship with the output code of a converter. As is clear from the figure, the current i flowing into the current/voltage conversion circuit can range from 0 to 15id depending on the state of each sensor (current id corresponds to the current flowing through the resistor Rd). For example, when all the sensors are off, that is, when the current i is 0, the output voltage of the current/voltage conversion circuit is the value of Vref, so the output of the A/D converter is 1111. Further, when all the sensors are in the on state, that is, when the current i is 15id, the output voltage V of the current/voltage conversion circuit is 0, so the output of the A/D converter is 0000.

In this way, the on/off state of each sensor can be changed to 4.
It can be obtained as a bit code, and the on/off status of each sensor can be detected from this code. In addition, when encoding the ON state of the sensor with bit 1 and the OFF state with bit 0, take the 1's complement for the output code of the A/D converter as shown in the figure. Then,
Obtainable.

[Brief explanation of drawings]

FIG. 1 shows a sensor circuit which is an embodiment of the present invention.
FIG. 2 is a diagram showing the relationship between the state of each sensor and the output code of the A/D converter in the same sensor circuit. Fig. 3 is a diagram showing an example of a conventional sensor circuit, Fig. 4 is a diagram explaining the operating principle of another conventional sensor circuit, and Fig. 5 is a diagram showing a specific example of the conventional sensor circuit. be. 1...A/D converter, 2...Current/voltage conversion circuit, SWa to SWd...Sensor, Ra to Rd...Resistance,
OP... operational amplifier, Vref... reference voltage.

Claims (1)

[Claims] 1. A plurality of sensors that are switched on and off are connected in parallel, and a resistor is connected in series to each sensor, and the magnitude of each resistor is set to a different power of 2, Furthermore, a current/voltage conversion circuit that converts the sum of the currents flowing through each sensor into a voltage, and an A/D converter that converts the output voltage of the current/voltage conversion circuit into A/D are provided, and this A/D converter is provided.
In a sensor circuit that detects the state of each sensor by the output of a converter, the current/voltage conversion circuit is configured with an inverting feedback circuit using an operational amplifier, and the A/D is connected to a reference voltage input terminal of the operational amplifier. A sensor circuit characterized in that a reference voltage is applied that is equal to the maximum input voltage of a converter and that is equal to a voltage that changes the output voltage of the current/voltage conversion circuit in the range from 0 potential to the reference voltage of the operational amplifier.