JPH0365870B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a distance measurement method using a received light amount detection method in which the distance to a target object is measured by projecting infrared light and measuring the received amount of reflected light. It is related to the device.

Conventional configuration and its problems Conventional distance measurement methods that project infrared light onto a target object and use the reflected light to measure distance include a received light amount detection method that uses the received amount of reflected light. Alternatively, a triangulation method using the receiving angle of reflected light is known.

The former method of detecting the amount of received light detects the amount of received light signals, that is, the level of received light, so there is no need for moving parts or expensive light receiving element arrays, and in addition, special consideration is given to the distance between the light emitter and the light receiver. It has the effect of eliminating the need for it.

However, the distance measurement principle of the above-mentioned method for detecting the amount of received light is that the amount of light emitted from the light emitting unit and the light emitted intensity are constant;
Since it is a method that measures the amount of attenuation of light corresponding to distance, when put into practical use as a device, it is necessary not only to keep the emitted energy constant, but also to measure distances accurately over long distances, which requires a large amount of emitted energy. Therefore, it is troublesome that great care must be taken in selecting the light projector, power source, etc. from the viewpoint of accuracy and the shape of the device.

Therefore, the applicant of this application first filed the patent application No. 58-224757.
No. 2, we propose a distance measuring method and a distance measuring device using a method for detecting the amount of received light that can solve the above-mentioned problems.

Such a proposal involves continuously changing the frequency of the infrared light projected onto the target object within a predetermined frequency band, and also changing the light receiving signal of the light receiving section obtained in response to the reflected light from the target object by resonance. It is characterized in that processing is performed via a tuning means having a frequency that can resonate with any frequency included in the predetermined frequency band, and one embodiment thereof is shown in FIG.

That is, to briefly explain the operation using the illustrated embodiment, the light projection frequency of the light projection section 1 is determined by the oscillation circuit section 3.
By supplying the charging voltage of the capacitor 6 charged by the constant current source 5 in the control circuit section 4 to the bases of the transistors 7 and 8 in the oscillation circuit section 3, By generating and supplying it to the drive circuit 2, the light emitting unit 1
It is made variable by controlling the energy supply operation to.

In other words, the transistor 7 in the oscillation circuit section 3
and 8 alternately conduct when the charging voltage of the capacitor 6 charged by the constant current source 5 is supplied.
As the charging voltage of the capacitor 6 starts to repeat the non-conducting state and the charging voltage of the capacitor 6 increases, the period of the inverting operation becomes shorter. The signal that appears is a pulse signal that shifts from low frequency to high frequency, and as a result of this pulse signal being supplied to the drive circuit 2, the energy supply to the light projecting section 1 is made to correspond to the above pulse signal. ,
This means that the so-called light projection frequency can be varied.

Incidentally, the light reflected from the target object due to the light projecting operation as described above is converted into a light reception signal by the light receiving section 9,
The received light signal is transmitted to the amplification unit 1 via a tuning circuit 10 having a resonant frequency at an arbitrary frequency included in the frequency band in which the light projection frequency is varied.
1 will be supplied.

That is, the received light signal is necessarily processed through resonance operation by passing through the tuning circuit 10 as described above, and the signal level is increased, and after being amplified by the amplifier section 11, a distance signal is generated. In the section 12, the signal is converted into an appropriate distance signal.

As is clear from the operation of the embodiment of the previous proposal illustrated in FIG. 1, which has been briefly described above,
The above proposal is characterized in that the operation of detecting the amount of received light corresponding to one light projecting operation is always performed through resonance operation. Therefore, even if the light emitting energy on the light emitting side is small, as in the case of a light emitting diode, for example, the resonant operation that always takes place greatly increases the light receiving efficiency, making it possible to accurately measure distances over long distances. Of course, since the light emitting diode described above can be used, the power supply device can also be made smaller.

However, in all of the disclosed embodiments including the embodiment shown in FIG. 1 in the above proposal, the light emission frequency is varied by analog processing using the charging voltage of the capacitor. It has disadvantages as shown below.

In other words, since the light emission frequency is variable through analog processing, as shown in Figure 2, the number of variable frequency pulse signals at any frequency included in any fixed period T _C and its vicinity is in the low frequency region. In the high frequency region, the number of pulse signals is small, and in the high frequency region, the number increases, and the number of pulse signals that can reach the resonant frequency is only one, if any.

On the other hand, it is known that the strength of the resonant operation is not stable unless a given number or more of pulse signals of the resonant frequency are supplied, and conversely, it becomes saturated if the strength is a predetermined number or more that is larger than the above-mentioned arbitrary number.

Therefore, in the frequency variable configuration described above,
Resonance is weak in the low frequency range and strong in the high frequency range.

As a result, if the resonant frequency changes due to changes in the standards of circuit components or the environment, although resonant operation will always occur, the strength of the resonance will fluctuate in conjunction with the change, for example. , it is conceivable that the robot performs an operation that causes a difference in the signal level detected for targets at the same distance.

In other words, as a distance measuring device that detects the amount of received light and obtains the signal level through resonance operation as distance information, the embodiment disclosed in the previous proposal in which the light emission frequency is changed in an analog manner is suitable for use with compact cameras, for example. There is no practical problem when applied to devices such as distance measuring devices that only need to obtain distance information with a certain range of width, but when trying to obtain more accurate distance information, it is not a preferred embodiment. It is impossible to say that there is.

Purpose of the Invention As mentioned above, the present invention has been made in consideration of the disadvantages of the embodiment of the invention previously proposed by the applicant, and its purpose is to digitally adjust the light emission frequency of the light projector. It is an object of the present invention to provide a distance measuring device using a method for detecting the amount of received light that utilizes resonance operation in which the intensity of resonance within a variable frequency band is kept constant through control.

Another object of the present invention is to digitally vary the light emitting frequency by supplying a predetermined number of pulse signals with stable resonance to the drive circuit of the light emitting section regardless of the low and high frequency regions. It is an object of the present invention to provide a distance measuring device using a method of detecting the amount of received light, which can keep the intensity of light constant.

Still another object of the present invention is to digitally convert the frequency at each reference time based on the time required to supply the drive circuit with the number of pulse signals that saturate the resonance strength in the low frequency region of the variable frequency. It is an object of the present invention to provide a distance measuring device that utilizes a method for detecting the amount of received light, in which the intensity of resonance is varied and the intensity of resonance is constant.

Structure of the Invention A distance measuring device using the received light amount detection method according to the present invention includes a light projecting section that projects infrared light onto a target object, a drive circuit that controls energy supply to the light projecting section, and a predetermined drive circuit that controls energy supply to the light projecting section. digital frequency setting means for outputting a predetermined number or more of pulse signals whose frequency is digitally varied within a frequency band and supplying the pulse signals to the drive circuit to digitally vary the light emission frequency of the light emission unit; a light receiving section that receives external light reflected from the target object; and a tuning means that has a tuning frequency that resonates with an arbitrary frequency included in the frequency band and selects a part of the light signal received by the light receiving section. an amplification section for amplifying the output of the tuning means; a distance signal generation means for converting the level of the signal output from the amplification section into a distance signal to the target object; and an energy source for each means of each of the above sections. It consists of a power source and a power switch that controls the supply of this power.

DESCRIPTION OF EMBODIMENTS FIG. 3 is an electrical circuit diagram showing an embodiment of a distance measuring device according to the present invention, and in the figure, parts with the same numbers as those in FIG. 1 have the same functions.

13 is an oscillation circuit that outputs a pulse signal of a predetermined frequency; 14 is a frequency divider circuit that divides the frequency of the pulse signal output from the oscillation circuit 13 to generate a reference clock signal; and 15 is a reference clock signal output from the frequency divider circuit 14. This figure shows a counting circuit that counts the number of objects.

Reference numeral 16 denotes an initial frequency setting means for setting the initial frequency of the light projection frequency to be varied;
By supplying a start signal to 6 ₁ , that is, a distance measurement start signal for starting a distance measurement operation, a digital signal indicating the number of the reference clock signals corresponding to the initial frequency to be set is outputted to a subtraction circuit 17, which will be described later. It outputs a control digital signal.

17 outputs a digital signal indicating the number of reference clock signals for setting the above-mentioned initial frequency using the control digital signal output from the initial frequency setting means 16, and also outputs the digital signal to the clock terminal ₁₇₁ . It shows a subtraction circuit that sequentially subtracts data by supplying a signal.

18 is the counting output of the counting circuit 15 and the subtracting circuit 1
A magnitude comparator which compares both the number signals with the subtraction output of 7 and outputs a coincidence pulse signal from the output terminal 18 ₁ when they match. 19 receives the coincidence signal output from the magnitude comparator 18 and outputs the output terminal 19 ₁ This figure shows a flip-flop circuit in which the output state of the circuit is inverted. It is also clear from FIG. 3 that the output of the flip-flop circuit 19 is supplied to the drive circuit 2.

Reference numeral 20 is a subtraction circuit which counts the falling or rising signals of the output signal output from the flip-flop circuit 19, that is, the falling signal or rising signal of the pulse signal, and outputs the signal from the output terminal ₂₀₁ when the count reaches a predetermined number N. 17 and a counting means for outputting a control signal for controlling its own operation.

Reference numeral 21 indicates final frequency setting means for setting the final frequency of the variable light projection frequency, and reference numeral 22 indicates a comparison between the output signal of the final frequency setting means 21 and the subtraction output of the subtraction circuit 17, and when the two match, the output terminal is 2
2 ₁ indicates a magnitude comparator that outputs an operation end signal, that is, a signal that ends the ranging operation.

Reference numeral 23 denotes an inverter that releases the reset state of the flip-flop circuit 19, that is, makes it ready for operation, by receiving a distance measurement start signal for starting the operation of the initial frequency setting circuit 12 and performing a distance measurement operation.

As is clear from the configuration described above,
In this embodiment, the functions of the oscillation circuit section 3 and the control circuit section 4 in the above-mentioned proposed embodiment shown in FIG.
This is what is attempted to be achieved with the digital frequency setting configuration shown in , and the operation will be explained below.

Now, when the power SW is turned on and the power E is supplied to each circuit section, when a distance measurement start signal that specifies the start of the distance measurement operation is generated, this signal is supplied via the inverter 23. The reset state of the oscillation circuit 13 and the flip-flop circuit 19 is released, and the initial frequency setting means 1
6 is an initial frequency determined by, for example, (n+1) reference clock signals set by itself.
A command signal is outputted to cause the subtraction circuit 17 to output a digital signal representing the above (n+1) number corresponding to _o+1 .

Therefore, the oscillation circuit 13 starts its oscillation operation, a reference clock signal of a predetermined frequency is outputted from the frequency dividing circuit 14, and the number thereof is counted by the counting circuit 15.

Further, the flip-flop circuit 19 is brought into an operating reference state in which it can operate by supplying the output signal from the magnitude comparator 18, and furthermore, the subtraction circuit 17 sends a digital signal indicating, for example, (n+1) flip-flops to the magnitude comparator 18. 18
It will be supplied to

The magnitude comparator 18 receives a counting digital signal of the reference clock signal of the counting circuit 15, and
Compare the digital signal corresponding to the initial frequency supplied from the subtraction circuit 17, and if the two match,
That is, in the previous example, the counting circuit 15 is (n+1)
When counting the number of flip-flops, a coincidence output signal is generated from the output terminal ₁₈₁ and supplied to the flip-flop circuit 19 and the counting circuit 15.

The flip-flop circuit 19 performs an operation of inverting its output level by supplying the output signal as described above, and the output signal of the flip-flop circuit 19 is supplied to the drive circuit section 2 and the counting circuit 20.

On the other hand, the counting circuit 15 has its counting contents up to that point reset by the coincidence output signal from the magnitude comparator 18, and then starts counting again.

That is, to explain using the previous example, the counting circuit 15 (n
+1) reference clock signals, the magnitude comparator 18 outputs a coincidence output signal, and the flip-flop circuit 19
This means that a pulse output whose output state is inverted even at a period determined by (n+1) reference clock signals is output.

Therefore, the drive circuit section 2 controls the operation of the light projecting section 1 according to the pulse signals from the flip-flop circuit 19, and the counting circuit 20 starts counting the pulse signals.

As mentioned above, the counting circuit 20 is configured so that the pulse signal output from the flip-flop circuit 19 is counted by a predetermined number N.
At the point when the subtraction circuit 17 is output from the output terminal ₂₀₁
It also outputs its own control signal, subtracts the output digital signal of the subtraction circuit 17, and resets its own counting operation.

That is, when the control signal from the counting circuit 20 is supplied to the clock terminal 171, the subtracting circuit ₁₇ outputs n digital signals indicating, for example, the number (n+1) of the reference clock signals that have been output so far. This means that it will be subtracted from the signal.

Therefore, after the counting circuit 20 outputs the control signal, the magnitude comparator 18 outputs a coincidence output signal when the counting circuit 15 counts n pieces of the reference clock signal, which is one less than the above-mentioned state. It turns out.

As a result, the flip-flop circuit 19 outputs a pulse signal whose output state is reversed in a shorter time than when counting (n+1) pieces, that is, a pulse signal having a higher frequency than in the case of light. That's why.

The counting operation of the high-frequency pulse signal by the counting circuit 20 is the same as in the previous case. Therefore, in such a case as well, if the predetermined number N is counted, the subtraction circuit 17 and itself are controlled. A control signal will be output.

From then on, the above-mentioned operations are repeated, and briefly stated, the light emitting state of the light emitting unit 1 is a predetermined number N of pulse signals whose frequency increases by one reference clock signal. It will be controlled by the column.

On the other hand, the digital output signal of the subtraction circuit 17 is also supplied to a magnitude comparator 22, and is compared with a signal corresponding to the final frequency set by the final frequency setting means 21.

That is, the final frequency setting means 21 has a function similar to that of the initial frequency setting means 16 and the subtraction circuit 17, and outputs a digital signal corresponding to an arbitrary number of reference clocks. This means that digital signals corresponding to x) are output.

Therefore, by the operation described above, the digital signals output from the subtraction circuit 17 are changed from the state corresponding to (n+1) to n, (n-1), and (n-2).
When the number reaches (n-x), the magnitude comparator 22 operates, and an operation end signal is output from its output terminal ₂₂₁ .

The operation end signal is a signal for terminating the ranging operation including the operations as described above, that is, a signal for terminating a series of ranging operations including the operations of the light receiving section 9, the tuning circuit 10, etc., although not mentioned in the above explanation. , is a signal that brings each circuit section into the state before the distance measurement start signal is supplied, and one distance measurement operation system is completed with the above operation.

Incidentally, the relationship between the reference clock signal and the pulse signal output from the flip-flop circuit 19 in the above explanation is schematically shown as shown in FIG. The output signals of the magnitude comparators 18 and 22 and the variable characteristics of the light projection frequency are shown.

As is clear from FIGS. 4A, 4B, and 4E, the flip-flop circuit 19 outputs N pulse signals having the same frequency, that is, signals with the same number of reference clock signals, and in addition, N pulse signals are output. Since the frequency increases by one reference clock signal each time the output ends, the light emitting section in the embodiment shown in FIG. 3 has digital light emitting frequency characteristics. be.

Therefore, by setting the predetermined number N, which is the number of pulse signals outputted by the above flip-flop circuit 19, to an arbitrary number that stabilizes the strength of resonance, the problem as proposed at the beginning will not occur. That's why.

In addition, in the embodiment shown in FIG. 3, the light emitting frequency of the light emitting section is configured to gradually increase, that is, it has the subtraction circuit 17, but of course, the light emitting frequency gradually decreases. It goes without saying that the light projection frequency may be set to such a characteristic that the following characteristics are obtained.

Furthermore, if a ceramic resonator such as a crystal is used as the reference oscillation source for the oscillation circuit 13, the oscillation frequency does not need to take into account variations in conduction potential of transistors or temperature changes, unlike multivibrators using transistors. It becomes stable, and since it is digital processing, the above-mentioned variable projection frequency configuration can be formed by a microcomputer, making it possible to obtain extremely stable frequency variable characteristics.

Furthermore, by increasing the frequency of the reference clock signal, the interval between variable frequencies can be reduced.
In reality, it goes without saying that analog-like continuously variable states can be obtained.

Further, the number of reference clock signals to be controlled for varying the frequency is a predetermined number as in the previous embodiment.
For example, if it is limited to one, the frequency variable characteristics will change little by little in the low frequency range and change greatly in the high frequency range, which may cause a difference in the probability of resonance for any given frequency. Therefore, in the case of practical use, it goes without saying that it is preferable to increase the number of controls of the reference clock signal in the low frequency range and to make the frequency change by the same frequency width.

FIG. 5 is a schematic electrical circuit diagram showing another embodiment of the distance measuring device according to the present invention, in which the same numbers as in FIG. 1 indicate the same functional members.

In FIG. 5, the figure number 24 is an oscillation circuit that generates a reference pulse signal every predetermined time T, and 25 is an input terminal 2.
By supplying the distance measurement start signal to 5 ₁ , the oscillation circuit 24
a counter that counts reference pulse signals generated by the counter and forms different output states depending on the counting state;
6 is the initial voltage value initially supplied to the oscillation circuit section 3
An initial value setting circuit that sets a digital signal corresponding to V ₁ in the adder 27, 27 is an initial value setting circuit 2
6 outputs a digital signal corresponding to the initial voltage value, and an adder 28 changes the state of the output digital signal in accordance with the output state of the counter 25; A D/A converter that outputs a corresponding arbitrary voltage value and supplies it to the oscillation circuit section is shown.

Note that during the predetermined period T during which the oscillation circuit 24 outputs the reference pulse signal, stable resonance strength can be obtained even in the low frequency region of the frequency band in which it is desired to vary the light projection frequency. That is, it goes without saying that the predetermined period is set to be longer than the time during which the pulse signals of the oscillation circuit sections 3 are supplied to the drive circuit 2 of the light projecting section 1 in a number that saturates the resonance strength.

Further, the initial voltage value V ₁ set by the adder 27 and the D/A converter 28 based on the output signal from the initial value setting circuit 26 is set to Needless to say, the conduction potential is set to be higher than the conduction potential of the transistor constituting the transistor.

The operation of the embodiment shown in FIG. 5 will be briefly described below.

When the distance measurement start signal is now generated with the power switch SW turned on and the power E being supplied to each circuit section, the counter 25 and the initial value setting circuit 26 enter the operating state, and the counter 25 turns on the oscillation circuit 24. , and the initial value setting circuit 26 outputs a control signal to control the operation of the adder 27 so that the adder 27 outputs a digital signal corresponding to the initial setting voltage value _V1 . do.

Therefore, the D/A converter 28 immediately outputs the initial setting voltage V ₁ and supplies it to the oscillation circuit section 3.

That is, in the case of the embodiment shown in FIG. 5, a voltage value V ₁ higher than the conduction potential of the transistor forming the oscillation circuit section 3 is supplied to the oscillation circuit section 3 at the same time as the ranging start signal is supplied. Therefore,
As a result, the oscillation circuit section 3 starts an oscillation operation at an initial frequency corresponding to the above-mentioned initial voltage value _V1 , and therefore, the light projecting section 1 is driven to be operated and controlled at an initial frequency ₁ corresponding to the above-mentioned voltage value _V1 . By the energy supply control operation of the circuit 2, a light projection operation is performed with the above-mentioned initial frequency ₁ as the light projection frequency.

On the other hand, after the above-mentioned point of supply of cut-off voltage V ₁ ,
When the predetermined period T has elapsed, the oscillation circuit 24 outputs a pulse signal, so the output state of the counter 25 changes, and the changed count output signal is sent to the adder 2.
7 will be supplied.

Therefore, the adder 27 outputs a digital signal different from the digital signal corresponding to the initial voltage value V ₁ that has been output up to that point, that is, a voltage value different from the initial voltage value V ₁ , for example, V ₂ . This means that a digital signal will be output.

When the D/A converter 28 receives a digital signal different from the initial one as described above, it naturally outputs a voltage value different from the initial setting voltage value _V1 , for example, _V2 .

As a result, the oscillation operation of the oscillation circuit section 3 that is operated by being supplied with the voltage value output from the D/A converter 28 becomes an operation having a frequency of, for example, ₂ , which is different from the initial frequency ₁ , and therefore the light projecting section 1 The light emission frequency will also be varied from ₁ to ₂ .

Hereinafter, each time a pulse signal is output from the oscillation circuit 24, that is, each time a predetermined period T elapses, the adder 2 changes the count output of the counter 25 as described above.
The digital output of 7 changes, and the D/A converter 2
An operation is performed in which the voltage value outputted from 8 is varied.

That is, the D/A converter 28 in the above operation
The output voltage state can be illustrated as shown in FIG. 6, for example. In the example shown in FIG. 6, the initial voltage V ₁ is set as the lowest voltage, and the output voltages are sequentially increased to V ₂ , V ₃ , . . . by the above-described operation.
This is an example in which the voltage V _o increases, and there is no need to describe it in detail, but the variable characteristics of the voltages V ₂ , _{V 3} . This is the time when the distance start signal is supplied.

Furthermore, the final voltage V _o can be set in various ways, such as by appropriately controlling the capacity of the counter 25 or adder 27, or by forcibly resetting each circuit to a non-operating state when a predetermined number of voltage fluctuations have ended. Needless to say, it can be set appropriately using the following means.

Further, contrary to the characteristics shown in FIG. 6, the light emission frequency of the light emission unit 1 may be controlled by setting the initial voltage value _V1 as the highest voltage value and sequentially lowering the output voltage of the D/A converter 28. There is no need to explain this in detail.

Effects of the Invention The present invention provides a distance measuring device using a received light amount detection method in which the light emitting frequency is varied in an arbitrary band and the received light signal is processed through resonance operation, in which the light emitting frequency is digitally varied. Therefore, the condition that the strength of resonance is constant can be easily satisfied,
That is, it is possible to easily supply a predetermined number of arbitrary frequency pulse signals with stable resonance strength, and to supply pulse signals of different frequencies based on a predetermined time when the resonance strength is saturated in the low frequency region. Therefore, it has the effect of being able to perform highly accurate ranging operations.

[Brief explanation of drawings]

Fig. 1 is a diagram of an embodiment of the invention previously proposed by the present applicant, Fig. 2 is a pulse signal diagram showing the number of signals included within a predetermined period Tc in an analog frequency variable configuration, and Fig. 3 4 is an electric circuit diagram showing one embodiment of the distance measuring device according to the present invention, and FIG.
A signal waveform diagram for explaining the operation of the embodiment shown in the figure, FIG. 5 is an electric circuit diagram showing another embodiment of the distance measuring device according to the present invention, and FIG. 6 is an embodiment shown in FIG. 5. 2A and 2B are voltage waveform diagrams showing an example of the output waveform of the D/A converter in FIG. DESCRIPTION OF SYMBOLS 1... Light emitting part, 2... Drive circuit, 3... Oscillation circuit part, 9... Light receiving part, 10... Tuning means, 11...
...Amplifying section, 12... Distance signal generating means, 13...
Oscillation circuit, 14... Frequency dividing circuit, 15, 20... Counting circuit, 16... Initial frequency setting means, 17...
Subtraction circuit, 18, 22...Magnitude comparator, 19...Flip-flop circuit, 21...
... Final frequency setting means, 24 ... Oscillation circuit, 25
...Counter, 26...Initial value setting circuit, 27...
...Adder, 28...D/A converter.

Claims (1)

[Scope of Claims] 1. A light projecting section that projects infrared light toward a target object, a drive circuit that supplies energy to the light projecting section by operating, and a drive circuit whose frequency is within a predetermined frequency band. digital frequency setting means for supplying a predetermined number or more of digitally variable pulse signals to the drive circuit to intermittent the operation of the drive circuit and digitally controlling the light emission frequency of the light emission section; a light receiving section that receives reflected light from the target object; and a tuning frequency that resonates with an arbitrary frequency within the predetermined frequency band, and a resonance operation is performed by receiving light receiving output from the light receiving section. a tuning means, an amplification section for amplifying a resonance output signal obtained by the resonance operation of the tuning means, and a distance signal generation means for converting the level of the output signal of the amplification section into a distance signal to the target object. , a distance measuring device using a received light amount detection method, which includes power sources for the light projector and the light receiver, and a power switch that controls supply of the power. 2. The digital frequency generation means includes an oscillation means that generates a reference clock signal, a first counting circuit that performs counting when the reference clock signal is supplied, and a frequency band that operates and varies when the distance measurement start signal is supplied. initial frequency setting means for generating a first control signal that causes one of the high or low frequencies that define the initial frequency to be set as the initial frequency;
A first digital signal indicating the number of the reference clock signals corresponding to one of the frequencies set as the initial frequency is outputted by supplying the control signal, and a second control signal is supplied. an arithmetic circuit that varies the content of the first digital signal by comparing the counting output of the first counting circuit and the first digital signal outputted by the arithmetic circuit, and when the two match, the counting circuit; a first magnitude comparator that outputs a coincidence output signal for resetting the counting contents; and a first magnitude comparator that generates a pulse signal whose output state is inverted when the coincidence output signal is supplied, and supplies it to the driving circuit of the light projecting section. a flip-flop circuit; a second counting circuit that counts the number of pulse signals output by the flip-flop circuit and outputs the second control signal and its own reset signal when the counted value reaches a predetermined number; final frequency setting means for outputting a second digital signal indicating the number of the reference clock signals corresponding to the final frequency forming the frequency band together with the initial frequency; a second digital signal output from the final frequency setting means; A second magnitude comparator that compares the first digital signal output from the arithmetic circuit and outputs an operation end signal that stops a series of ranging operations when the two match. A distance measuring device using the received light amount detection method described in item 1. 3 The digital frequency setting means includes an oscillation circuit section that outputs a pulse signal of a frequency corresponding to the supplied voltage value and supplies it to the driving circuit of the light projecting section, and one low frequency that forms the limit of the frequency band to be varied. an oscillation circuit that outputs a reference pulse signal every arbitrary period longer than the time during which the oscillation circuit section can output a number of the pulse signals such that the strength of resonance by the tuning means is saturated in the region; A counter, a D/A converter that outputs a voltage value according to the supplied first digital signal and supplies it to the oscillation circuit section, and the oscillation circuit section malfunctions when the distance measurement start signal is supplied. an initial value setting circuit that sets and outputs a second digital signal corresponding to a voltage value that is not performed; and an initial value setting circuit that outputs the second digital signal from the initial value setting circuit as the first digital signal and counts the counter. A distance measuring device using the received light amount detection method according to claim 1, comprising an adder that sequentially varies the first digital signal according to a change in output.