JPH04343073A - Simplified system for monitoring voltage - Google Patents

Abstract

PURPOSE:To obtain a simplified system for monitoring voltage which monitors the voltage in a simple manner. CONSTITUTION:A processor 6 has a voltage monitoring processing means. When started, the voltage monitoring processing means conducts a processing of closing a switching means 5. When the switching means 5 is closed, the charge of a capacitor C is discharged. After the discharge is completed, the voltage monitoring processing means conducts, a processing of opening the switching means 5, while it starts time counting. A time count value at the time point when the output of a comparator 3 is switched over from one level to the other is stored, and a voltage at a voltage measuring point is determined by using this time count value.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simple voltage monitoring system that allows voltage to be easily measured.

0002

2. Description of the Related Art FIG. 6 is a diagram showing a conventional example of a photodiode output monitoring system. In the figure, 1 is a photodiode, 2 is a phototransistor, 3 is a comparator, R1 is a resistor, and R2 is a variable resistor. When the light output from the photodiode 1 is input to the phototransistor 2, a current flows through the phototransistor 2, and a current also flows through the resistor R2. The voltage of the resistor R2 is applied to the + side input terminal of the comparator 3, and the reference voltage Vref is applied to the - side input terminal of the comparator 3. When the voltage at the + side input terminal of the comparator 3 is higher than the voltage at the - side input terminal, the comparator 3 outputs a high level signal.

FIG. 7 is a diagram showing another conventional example of the photodiode output monitoring system. In the same figure, 4 is A/
A D converter is shown. Note that the same reference numerals as in FIG. 6 indicate the same parts. In the conventional example shown in FIG. 7, the voltage of the resistor R2 is input to the A/D converter 4, and digital data is output from the A/D converter 4.

0004

In the conventional example shown in FIG. 6, it is possible to know whether the voltage across the resistor R2 is higher or lower than the reference voltage Vref. However, if the voltage is higher than the reference voltage, it is not possible to know how much higher it is. The voltage across the resistor R2 decreases due to the adhesion of dust and aging. In the conventional example shown in Fig. 7, if the voltage is higher than the reference voltage, it is possible to know how high it is, but the conventional example shown in Fig. 7 requires an A/D converter, so the number of parts and cost increase. It has some drawbacks.

The present invention was created in view of this point, and an object of the present invention is to provide a simple voltage monitoring system that can easily monitor voltage without using an A/D converter or the like.

[0006]

[Means for Solving the Problems] FIG. 1 is a diagram illustrating the principle of the present invention. The simple voltage monitoring method of the present invention includes a resistor R whose one end is connected to a voltage measurement point, a capacitor C connected between the other end of the resistor R and a predetermined potential, and a capacitor C connected between one end of the resistor R and a predetermined potential. switch means 5 provided and a reference voltage source V
ref and a comparator 3 to which the voltage of the capacitor C is applied to one input terminal and the reference voltage Vref to the other input terminal, and the output of the comparator 3 is inputted, and the switch means 5 can be turned on/off. The processor 6 has a voltage monitor processing means, and when the voltage monitor processing means is activated, (1) performs processing for turning on the switch means 5; After performing the process of ■■, on condition that the capacitor C is completely discharged, a process is performed to turn off the switch means 5, and time counting is started, and after performing the process of ■■, the comparator 3
Performs processing to store the time count value at the time the output is switched from one level to the other, and ■
The present invention is characterized in that it is configured to perform processing for determining the voltage value at the voltage measurement point using the time count value stored in step (3).

[0007]

[Operation] As shown in FIG. 1, a CR integration circuit is provided at the input stage of the comparator 3, and a switch means 5 for discharging is provided.
will be established. When monitoring the voltage, the switch means 5 is turned on to discharge the charge in the capacitor C. Next, a timer (either a hard timer or a soft timer) counts the time t from the moment when the switch means 5 is turned off to the moment when the output of the comparator 3 is switched from one level to the other level. The input voltage E is determined from this time.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is an electrical circuit diagram of one embodiment of the present invention. In the figure, 1 is a photodiode, 2 is a phototransistor, 3 is a comparator, 5 is a transistor, 6 is a microprocessor, C is a capacitor, R is a resistor, R1 is also a resistor, R2 is a variable resistor, v is a capacitor C
and E indicate the voltage of the resistor R2, respectively.

When the light output from the photodiode 1 is received by the phototransistor 2, a current flows through the phototransistor 2 and the resistor R2. When transistor 5 is off, capacitor C is connected to resistor R
It is charged by voltage E via . The voltage of the capacitor C is applied to the + side input terminal of the comparator 3, and the reference voltage Vref is applied to the - side input terminal of the comparator 3. When the voltage at the + side input terminal of the comparator 3 is higher than the voltage at the - side input terminal, the comparator 3 outputs a high level signal. The output of the comparator 3 is input to the interrupt terminal (or normal input port) of the microprocessor 6. Microprocessor 6 can control on/off of transistor 5.

When measuring the voltage E of the resistor R2,
The microprocessor 6 turns on the discharge signal,
Turn on transistor 5. When transistor 5 is turned on, the charge in capacitor C is discharged. Whether or not the capacitor C is completely discharged is determined by the on-time of the transistor 5. The discharge time is determined by the time constant of the CR integration circuit (τ=C
Approximately 97% of the discharge will be completed by setting the time to 3 times the time constant of R), so if you set the time to be approximately 5 times the time constant, the capacitor C
It can be determined that the battery has been completely discharged.

Under the condition where the voltage of the capacitor C becomes approximately zero, the microprocessor 6 turns off the discharge signal and starts time counting using a hard timer or a soft timer. When the discharge signal is turned off, transistor 5 is turned off and the voltage of capacitor C gradually increases. The voltage of capacitor C is Vr
When ef is exceeded, the output of comparator 3 goes high. The microprocessor 6 stores the time count value t when the output of the comparator 3 becomes high level, and calculates the value of the voltage E based on the capacitance of the capacitor C, the resistance value of the resistor R, and the time t. The microprocessor 6 actually converts time t into voltage E by having a conversion table (address=time count value, data=voltage E). Note that as the capacitor C, a ceramic capacitor having a small rate of change in capacitance due to temperature is used.

The voltage v across the capacitor C is v=E(1
-et/CR)
It is expressed as (1). From the above formula, time t is t=-CRloge (1-v/E)
It is expressed as (2).

FIG. 3 is a time chart showing the operation of the embodiment shown in FIG. Discharge signal is on (high level)
Then, the voltage v of the capacitor C gradually decreases from E, and when it becomes lower than the reference voltage Vref, the output of the comparator 3 becomes a low level. The voltage v of the capacitor C eventually becomes approximately zero. The microprocessor 6 turns off the discharge signal and starts time counting under the condition that the voltage v of the capacitor C becomes approximately 0. When the discharge signal is turned off, the voltage v of capacitor C
gradually increases, and when it exceeds the reference voltage Vref, the output of the comparator 3 is switched from low level to high level. The microprocessor 6 stores the time count value at the time when the comparator output switches from a low level to a high level, and uses this time count value to determine the value of the voltage E.

FIG. 4 is a diagram showing a paper detection sensor. In the figure, 7 indicates a support frame, and 8 indicates a paper sheet. The printer device has a paper detection sensor as shown in FIG. Paper dust etc. may adhere to the paper detection sensor and the output level may drop (it is determined that there is paper even though there is no paper). Check whether the output level of the paper detection sensor is normal using the method.

FIG. 5 is a diagram showing a processing flow when checking the output level of the paper detection sensor. Activation of this processing flow may be performed once before feeding paper as one of a series of initialization processing (memory check, head centering, etc.) when the power is turned on. In step S1, a discharge constant D (D is a positive integer) is set in a counter N. Discharge time T
D is expressed as TD=D×tx (sec). To completely discharge capacitor C, CR
TD should be about 5 times the time constant τ, and D=
Set TD/tx = 5τ/tx. Note that tx is the time required to go through the loop of steps S3 and S4.

[0016] In step S2, the output port is turned on,
Turn on transistor 5. When the transistor 5 turns on, the capacitor C starts discharging. In step S3, it is checked whether N=0. If Yes, step S
If the answer is No, the process advances to step S4. In step S4, N is incremented by -1. Next, the process returns to step S3. In step S5, N is set to 0. This N is a counter for measuring the time until the output of the comparator changes from low to high.

In step S6, the output port is turned off in order to start charging the capacitor C. Step S7
Now check whether the input port is at high level. If the level is high, the process advances to step S9; if the level is low, the process advances to step S8. In step S8, N is incremented by 1. Next, the process returns to step S7.

In step S9, it is checked whether N is less than or equal to Y. If Yes, proceed to step S11;
If so, proceed to step 12. Note that Y is a determination count (time). The constant Y will be explained. In order for the paper detection sensor to operate properly, the VS
If an output voltage of volts or higher is required, the time tS for the comparator output to go from low to high when the output voltage is VS is: tS = -CRloge (1-Vref /VS)
When the measured time T is greater than tS, the sensor output is smaller than VS, and when T is less than ts, the sensor output is greater than VS. Therefore, Y set here is set as Y=ts/ty. However, ty is in steps S7 and S8
This is the time required to complete one loop.

In step S11, it is determined that it is normal. In step S12, abnormality processing such as turning on a check lamp is performed.

[0020]

As is clear from the above description, according to the present invention, voltage can be monitored with a simple configuration. Further, since the portion surrounded by the dotted line in FIG. 2 is versatile, it is also possible to integrate it into one chip.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention.

FIG. 2 is an electrical circuit diagram of one embodiment of the present invention.

FIG. 3 is a time chart showing the operation of the embodiment of FIG. 2;

FIG. 4 is a diagram showing a paper detection sensor.

FIG. 5 is a diagram showing a processing flow.

FIG. 6 is a diagram showing a conventional example of a photodiode output monitoring method.

FIG. 7 is a diagram showing another conventional example of the photodiode output monitoring method.

[Explanation of symbols]

1 Photo diode 2 Photo transistor 3 Comparator 4 A/D converter 5 Transistor 6. Microprocessor C Capacitor R Resistance R1 Resistance R2 Variable resistance v Voltage of capacitor C E Voltage of resistor R2

Claims (1)

[Claims] Claim 1: A resistor R having one end connected to a voltage measurement point, a capacitor C connected between the other end of the resistor R and a predetermined potential, and a switch provided between one end of the resistor R and a predetermined potential. Means (5), a reference voltage source Vref, a comparator (3) to which the voltage of the capacitor C is applied to one input terminal and the reference voltage Vref to the other input terminal, and an output of the comparator (3). A simple voltage monitoring system comprising a processor (6) which can turn on/off a switch means (5) as well as input, the processor (6) having a voltage monitor processing means, and the voltage monitor processing means , when started, ■ performs processing to turn on the switch means (5), and ■
After carrying out the process (2), on the condition that the capacitor C is completely discharged, a process is carried out to turn off the switch means (5), and time counting is started, and after carrying out the process (2), A process of storing the time count value at the time when the output of the comparator (3) is switched from one level to the other level, and calculating the voltage value at the voltage measurement point using the time count value stored in ■ ■. A simple voltage monitoring method characterized by being configured to perform.