JP2000259296A - Digital input circuit with coupled photocoupler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption of a photocoupler when a digital contact signal, etc., are inputted in a microcomputer by using the photocoupler. SOLUTION: In a digital input circuit formed by connecting a light emitting element LED 1 of a photocoupler PC1 with a digital contact signal circuit 3 and connecting a light receiving eleusent Tr1 of the photocoupler PC1 with a digital input circuit 4 of the microcomputer, a light emitting element LED2 of a photocoupler PC2 is provided on a digital output circuit 5 of the microcomputer, a light receiving element Tr2 of the photocoupler PC2 is provided in serial with the light emitting element LED1 of the digital contact signal circuit 3, the light emitting element LED2 of the photocoupler PC2 is turned on just before a state of a contact signal circuit is read by a digital input port DI of the microcomputer and the light emitting element LED2 of the photocoupler 2 is turned off just after the state of the contact signal circuit is read by the input circuit 4 of the microcomputer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocoupler for reading digital contact signals by an insulated circuit coupling element using a photocoupler for inputting digital contact signals, such as sensors and limit switches, to a microcomputer. The present invention relates to a combined digital input circuit.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a circuit for inputting a digital contact signal or the like to a microcomputer using a conventional photocoupler. In FIG. 5, 1 is a digital contact signal circuit, SW is a switch such as a sensor or a limit switch, BT is a DC power supply, and LED is a photocoupler PC.
Is a light emitting element. Reference numeral 2 denotes a digital input circuit of the microcomputer, and Tr denotes a light receiving element such as an output transistor of the photocoupler PC, which is connected to the digital input port DI of the microcomputer and turns on / off the switch SW.
Read off state. That is, this circuit is a switch SW
Is closed, a current flows from the DC power supply BT and the photocoupler P
C turns on. This allows the digital input port DI
Is at H (High) level, and when the switch SW is open, the photocoupler PC is in an inactive state, so that the digital input port DI is at L (Low) level. Therefore, the microcomputer can read the ON / OFF state of the switch SW at a required timing.

[0003]

However, in this conventional circuit, since the light emitting element LED of the photocoupler PC is always turned on while the switch SW is closed, a current of several mA to several tens mA flows to reduce the power. However, there is a problem that the power consumption of this portion cannot be reduced despite the low power consumption of the device. The present invention relates to a photocoupler PC
The power supply to the light emitting element LED on the primary side is
The ON / OFF state of W is performed only while the microcomputer is reading the signal.
The power consumption supplied to C is greatly reduced.

[0004]

A photocoupler-coupled digital input circuit according to the present invention has a light-emitting element of a first photocoupler connected to a digital contact signal circuit, and the first input circuit connected to a digital input circuit of a microcomputer. A photocoupler-coupled digital input circuit to which a light receiving element of a photocoupler is connected and reads the on / off state of the contact signal circuit by a digital input circuit of the microcomputer, wherein a second photocoupler is connected to a digital output circuit of the microcomputer. And a light receiving element of the second photocoupler is provided in series with a light emitting element of the first photocoupler of the digital contact signal circuit, and a digital input circuit of the microcomputer is provided with the contact signal circuit. Immediately before reading the on / off state of The light emitting element of the photocoupler is turned on, and the light emitting element of the second photocoupler is turned off immediately after the digital input circuit of the microcomputer reads the on / off state of the contact signal circuit. It is characterized by the following.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing one embodiment of a photocoupler-coupled digital input circuit according to the present invention, wherein 3 is a digital contact signal circuit, SW is a switch such as a sensor or limit switch, and BT is a switch. A DC power supply, LED1 is a light emitting element of the photocoupler PC1, and Tr2 is a light receiving element such as an output transistor of the photocoupler PC2. Numeral 4 denotes a digital input circuit of the microcomputer, Tr1 denotes a light receiving element such as an output transistor of the photocoupler PC1, and a digital input port DI of the microcomputer.
To read the ON / OFF state of the switch SW. 5 is a digital output circuit of the microcomputer, LED2 is a light emitting element of the photocoupler PC2,
The microcomputer is connected to the digital output port DO of the microcomputer, and the microcomputer turns on / off the switch SW.
It is driven only for a short time when the off state is read.

Next, the operation of the circuit diagram of FIG. 1 will be described. In the normal state, the digital output port DO connected to the microcomputer is set at the L level, and the photocoupler PC2 is turned off. Therefore, even if the switch SW of the contact signal circuit 3 is closed, the DC power supply BT
Does not supply power to the light emitting element LED1 of the photocoupler PC1.

When the microcomputer reads the on / off operation state of the switch SW of the contact signal circuit 3, that is, as shown in the flowchart of FIG. To level. Thereby, the photocoupler PC2
Is turned on, and the digital input port DI can read the on / off state of the switch SW. That is, at this time, when the switch SW is closed, a current flows through the photocoupler PC1, and the digital input port DI of the microcomputer goes to the H level. If the switch SW is open, the photocoupler P
No current flows through C1, and the digital input port DI goes to L level. Then, the microcomputer can read the state.

When the reading is completed, the microcomputer returns the digital output port DO to the L level, and can read the ON / OFF operating state of the switch SW at a required sampling period. The transition of the digital output port DO to the L level turns off the photocoupler PC2, and the current of the DC power supply BT does not flow through the contact signal circuit 3 even when the switch SW is closed. As described above, the microcomputer operates the switch SW.
Current flows through the contact signal circuit 3 only for a short time to cover the moment of reading the ON / OFF state of
Power consumption can be significantly reduced.

The power consumption supplied to the light emitting element LED1 of the contact signal circuit is, for example, as shown in FIG. 3 when a conventional digital input circuit is compared with the same circuit of the present invention. FIG. 3A shows a current supply state of the conventional contact signal circuit 1. When the sampling cycle for reading the digital input port DI is 50 ms, the current supplied to the light emitting element LED of the photocoupler PC while the switch SW is on is shown. The power supply averages 50 ms per cycle.

On the other hand, in the case of the present invention, FIG.
As shown in (b), the digital output port DO may be set to the H level only during the period covering the reading of the digital input port DI. Therefore, the photocoupler PC
The period during which power is supplied to one light emitting element LED1 is sufficient only for the period corresponding to the H level of the digital output port DO. If the H level period of the digital output port DO is, for example, 200 μs, the average per cycle is 200 μs.
The power supply period to the photocoupler PC1 is 1/500 of that of the conventional circuit, and the power consumption is greatly reduced.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 4 shows a configuration in which the case where the polarity of the DC power supply BT of the contact signal circuit 3 is connected in the opposite direction is reversed, and the light emitting element L of the photocoupler PC1 is provided.
A diode D1-D for polarity conversion is connected in parallel to a series circuit of the ED1 and the light receiving element Tr2 of the photocoupler PC2.
4 is connected as a bridge circuit. Thus, regardless of whether the polarity of the DC power supply BT is positive or negative with respect to the photocouplers PC1 and PC2, a current in the operation direction can flow through the light emitting element LED1 of the photocoupler PC1 and the transistor Tr2 of the photocoupler PC2.

[0012]

As described in detail above, in order to read out the operation state of the digital contact signal, the current is always applied to the light-emitting element of the photocoupler when the contact is on. According to the invention, the power consumption of the device can be reduced by applying a current to the light emitting element of the photocoupler for an extremely short time only when reading out the operation state of the digital contact signal. It greatly contributes to downsizing and downsizing.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a photocoupler-coupled digital input circuit according to the present invention.

FIG. 2 is a flowchart for explaining the operation of the photocoupler-coupled digital input circuit of the present invention.

FIG. 3 is an operation waveform diagram for comparing the power consumption of the photocoupler between the conventional circuit and the circuit of the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the photocoupler-coupled digital input circuit of the present invention.

FIG. 5 is a circuit diagram showing an example of a conventional photocoupler-coupled digital input circuit.

[Explanation of symbols]

 1,3 Digital contact signal circuit 2,4 Input circuit to microcomputer of contact signal 5 Output circuit to microcomputer SW switch BT DC power supply PC, PC1, PC2 Photocoupler LED, LED1, LED2 Light emitting element Tr, Tr1, Tr2 Light receiving element DI Digital input port DO Digital output port D1 to D4 Diode

Claims (2)

[Claims] A light emitting element of a first photocoupler is connected to a digital contact signal circuit, and a light receiving element of the first photocoupler is connected to a digital input circuit of a microcomputer. A photocoupler-coupled digital input circuit for reading on / off states by a digital input circuit of the microcomputer, wherein a second digital output circuit is provided to the microcomputer.
And a light receiving element of the second photocoupler is provided in series with the light emitting element of the first photocoupler of the digital contact signal circuit, and the digital input circuit of the microcomputer is Immediately before reading the on / off state of the contact signal circuit, the light emitting element of the second photocoupler is turned on, and immediately after the digital input circuit of the microcomputer reads the on / off state of the contact signal circuit, the second A photocoupler-coupled digital input circuit, wherein the light-emitting element of the second photocoupler is turned off. 2. A diode bridge circuit for polarity conversion is connected in parallel to a series circuit of the light emitting element of the first photocoupler and the light receiving element of the second photocoupler of the digital contact signal circuit. 2. The photocoupler-coupled digital input circuit according to claim 1, wherein said first and second photocouplers operate regardless of the polarity of the DC power supply of said contact signal circuit.