detection circuit

Abstract

To provide a detection circuit capable of detecting the connection status of a microphone without a dedicated detection terminal for detecting the connection.SOLUTION: A detection circuit is a detection circuit for detecting the connection status of a microphone that is powered by superimposing the power supply voltage on a pair of differential signal lines. The detection circuit measures the voltage of one of the pair of differential signal lines, and detects that the microphone is not connected when the measured voltage remains higher than a first threshold (V1) or lower than a second threshold (V2) for a predetermined period.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a detection circuit and a detection method.

Background Art

[0002] An information processing device exemplified by an in-vehicle device is connected to a device called a microphone, a microphone unit, a microphone module, etc. (hereinafter, microphone). Whether the microphone is connected to the information processing device can be detected, for example, by providing a dedicated detection terminal that outputs a signal indicating the connection.

[0003] However, when such a dedicated detection terminal is provided, terminals other than the signal terminal that outputs the signal detected by the microphone are provided, complicating the interface between the information processing device and the microphone.

[0004] Therefore, there may be a case where it is desired to connect the information processing device and the microphone with a simple interface without a dedicated detection terminal.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] One aspect of an embodiment of the present disclosure is to enable detection of the connection state of electronic components in a microphone that does not have a dedicated detection terminal for detecting connection.

Means for Solving the Problems

[0007] A first aspect of this disclosure is illustrated by a detection circuit. This detection circuit detects the connection status of a microphone powered by a power supply voltage superimposed on a pair of differential signal lines, and detects that the microphone is not connected when the voltage on one of the pair of differential signal lines is higher than a first threshold (V1) or lower than a second threshold (V2) for a predetermined period of time.

[0008] Furthermore, a second aspect of this disclosure is illustrated by another detection circuit. This detection circuit measures the voltages of both of the pair of differential signal lines and detects that the microphone is disconnected when the voltage of one of the pair of differential signal lines is higher than a first threshold (V1) and the voltage of the other is lower than a second threshold (V2). [Effects of the Invention]

[0009] This detection circuit can detect the connection status in microphones that do not have a dedicated detection terminal for detecting connections. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a diagram illustrating the configuration of the in-vehicle device in Comparative Example 1. [Figure 2] Figure 2 is a diagram illustrating the configuration of the in-vehicle device according to Embodiment 1. [Figure 3] Figure 3 illustrates the audio signals output from the + output terminal and the - output terminal. [Figure 4] Figure 4 is a diagram illustrating the configuration of the in-vehicle device according to Embodiment 1. [Figure 5] Figure 5 is a diagram illustrating the configuration of the in-vehicle device according to Embodiment 1. [Figure 6] Figure 6 is a diagram illustrating the structure of a microphone unit. [Figure 7] Figure 7 illustrates a differential receiver included in a hands-free circuit. [Figure 8] Figure 8 illustrates a differential receiver included in a hands-free circuit. [Figure 9]FIG. 9 is a diagram illustrating an equivalent circuit for a DC signal of an in-vehicle device when a microphone unit is connected. [Figure 10] FIG. 10 is a diagram illustrating an equivalent circuit for a DC signal of an in-vehicle device when the microphone unit is not connected. [Figure 11] FIG. 11 is an equivalent circuit for explaining the values of VDET1 and VDET2 when an antenna short circuit or a ground short circuit occurs with the microphone unit connected. [Figure 12] FIG. 12 is a timing chart illustrating changes in the values of VDET1 and VDET2 detected by the microcontroller 111 when an antenna short circuit, a ground short circuit, or the microphone unit being disconnected occurs from the connected state. [Figure 13] FIG. 13 is another example of a timing chart illustrating changes in the values of VDET1 and VDET2 detected by the microcontroller 111 when an antenna short circuit, a ground short circuit, or the microphone unit being disconnected occurs from the connected state. [Figure 14] FIG. 14 is a flowchart illustrating the processing of the microcontroller of the in-vehicle device. [Figure 15] FIG. 15 is a flowchart illustrating the processing according to Comparative Example 2. [Figure 16] FIG. 16 is a diagram illustrating problems in the processing of Comparative Example 2. [Figure 17] FIG. 17 is a diagram illustrating the configuration of an in-vehicle device according to Embodiment 2. [Figure 18] FIG. 18 is a flowchart illustrating the processing of the in-vehicle device of Embodiment 2. [Figure 19] FIG. 19 is a diagram illustrating the configuration of an in-vehicle device according to Embodiment 3.

MODE FOR CARRYING OUT THE INVENTION

[0011] Hereinafter, referring to the drawings, the detection circuit and detection method of the disclosed embodiments will be described. First, the configuration of Comparative Example 1 is illustrated, and then Embodiment 1 and below are described.

[0012] <Comparative Example 1> FIG. 1 is a diagram illustrating the configuration of the in-vehicle device 501 of Comparative Example 1. In FIG. 1, a microphone unit 502 connected to the in-vehicle device 501 is also illustrated. The in-vehicle device 501 includes, for example, a connection detection circuit 511, a hands-free circuit 512, a power supply circuit 513, and the like. Further, four terminals, namely, a power supply terminal, a + terminal, a GND terminal (also referred to as a - terminal), and a detection terminal, are illustrated for the microphone unit 502.

[0013] The in-vehicle device 501 and the microphone unit 502 are connected via the four terminals. The power supply circuit 513 supplies power to the microphone unit 502 via the power supply terminal. The hands-free circuit 512 acquires a sound signal detected by the microphone unit 502 via the + terminal and the GND terminal. For example, the microphone unit 502 outputs a single-ended signal with respect to the GND terminal to the + terminal. The connection detection circuit 511 detects the presence or absence of connection between the in-vehicle device 501 and the microphone unit 502 based on a signal (for example, a voltage) from the detection terminal. For example, the microphone unit 502 supplies a predetermined voltage to the detection terminal. When the predetermined voltage is detected at the detection terminal, the connection detection circuit 511 determines that the microphone unit 502 is normally connected to the in-vehicle device 501, and displays the determination result on a display device or a light-emitting device provided in the in-vehicle device 501.

[0014] <Embodiment 1> (Configuration) Hereinafter, the in-vehicle device 1 of Embodiment 1 will be described with reference to FIGS. 2 to 14. FIG. 2 is a diagram illustrating the configuration of the in-vehicle device 1 of Embodiment 1. In FIG. 1, a microphone unit 2 is also illustrated as an example of a microphone connected to the in-vehicle device 1. The in-vehicle device 1 includes, for example, a connection detection circuit 11, a hands-free circuit 12, a power supply circuit 13, and the like. Further, two terminals, namely, a + output terminal and a - output terminal, are illustrated for the microphone unit 2. That is, in the example of FIG. 2, the in-vehicle device 1 and the microphone unit 2 are connected by a two-wire interface.

[0015] Microphone unit 2 outputs the detected sound signal as a differential signal (or difference value) between the + output terminal and the - output terminal. However, compared to microphone unit 502 in Figure 1, microphone unit 2 in Figure 2 does not have a power terminal, and there is no detection terminal for detecting the connection status of microphone unit 2.

[0016] Therefore, the in-vehicle unit 1 to which the microphone unit 2 is connected cannot perform connection detection using a dedicated detection terminal. For this reason, in Embodiment 1, the in-vehicle unit 1 detects the connection status of the microphone unit 2 using at least one of the + output terminal and - output terminal, which output a differential signal.

[0017] Furthermore, the in-vehicle unit 1 supplies power to the microphone unit 2 via the + output terminal and - output terminal, which output sound signals. That is, DC power is supplied to the microphone unit 2 from the + output terminal and - output terminal, superimposed on the sound signal output from the microphone unit 2. Therefore, the power supply voltage is superimposed and supplied to the signal line connected to the + output terminal and the signal line connected to the - output terminal, which are a pair of differential signal lines. For this reason, it is desirable that the in-vehicle unit 1 be able to detect a short circuit (hereinafter referred to as a "high-power fault") to the positive power supply voltage of at least one of the + output terminal and - output terminal, and a short circuit (hereinafter referred to as a "ground fault") to the ground potential of at least one of the + output terminal and - output terminal.

[0018] Figure 3 illustrates the audio signals output from the + output terminal and the - output terminal. In Figure 3, the signals from the + output terminal and the - output terminal are output between the ground potential (GND (0V)) and the power supply voltage (Vcc). In Embodiment 1, for example, the + output terminal is biased to the + terminal midpoint potential.

[0019] In Figure 3, the spacing between the dotted lines drawn parallel to each other in the vertical direction (up and down direction in the figure, along the axis of the signal amplitude) illustrates the sampling interval at which the in-vehicle unit 1 detects the signals from the + output terminal and the - output terminal. For example, the in-vehicle unit 1 detects the signals from the + output terminal and the - output terminal at this sampling interval and determines the connection status of the microphone unit 2.

[0020] Figure 4 is a diagram illustrating the configuration of the in-vehicle unit 1A of Embodiment 1. In the in-vehicle unit 1A, the connection detection circuit 11 determines the connection status between the in-vehicle unit 1A and the microphone unit 2 based on the signal from the + output terminal of the microphone unit 2. As shown in Figure 4, the in-vehicle unit 1A supplies power from the power supply circuit 13 to the + output terminal of the microphone unit 2 via resistor R1. The - output terminal of the microphone unit 2 is grounded via resistors R2 and R3 connected in series. Hereafter, the signal from the + output terminal of the microphone unit 2 detected by the connection detection circuit 11 will be referred to as VDET1. Note that resistor R2 is included to ensure consistency with the explanation of the in-vehicle unit 1B described later, and resistor R2 may be omitted, or the series combination of resistors R2 and R3 may be referred to as resistor R3 (the same applies to Figure 7).

[0021] Figure 5 illustrates the configuration of the in-vehicle unit 1B of Embodiment 1. The in-vehicle unit 1B is a modified version of the in-vehicle unit 1A. In the in-vehicle unit 1B, the connection detection circuit 11 determines the connection status between the in-vehicle unit 1B and the microphone unit 2 by the signal obtained by dividing the signal from the negative output terminal of the microphone unit 2 by resistors R2 and R3. However, resistor R2 may be omitted. If resistor R2 is omitted, the connection detection circuit 11 directly detects the signal from the negative output terminal of the microphone unit 2 and determines the connection status between the in-vehicle unit 1B and the microphone unit 2.

[0022] Figure 6 illustrates the structure of the microphone unit 2. The equivalent circuit of the microphone unit 2 is also shown in Figure 6. The microphone unit 2 comprises a sound detection unit 21 and a differential driver 22. The sound detection unit 21 generates an electrical signal from fluctuations in the air caused by sound. The differential driver 22 amplifies the electrical signal generated by the sound detection unit 21 and outputs it as a differential signal between the + output terminal and the - output terminal. The DC signal is blocked between the + output terminal and the - output terminal by capacitors 23 and 24, respectively.

[0023] From the perspective of the hands-free circuit 12 of the in-vehicle unit 1, to which the + output terminal and - output terminal are connected, the microphone unit 2 can be considered an electronic circuit with an output impedance Zm connected between the + output terminal and the - output terminal. Therefore, in the explanations from Figure 7 onward, the operation of the in-vehicle unit 1 may be described by replacing the microphone unit 2 with the output impedance Zm. Also, when in-vehicle units 1A, 1B, etc. are referred to collectively, they are simply called in-vehicle unit 1.

[0024] Figure 7 illustrates a differential receiver 121 included in the hands-free circuit 12 of the in-vehicle unit 1A illustrated in Figure 4. In Figure 7, a microcomputer or microcontroller (hereinafter referred to as microcontroller 111) is further illustrated as an example of a control unit included in the connection detection circuit 11. The differential receiver 121 receives the differential signal from the microphone unit 2 and supplies a single-ended audio signal to the hands-free circuit 12. In Figure 7, capacitors C1 and C2 are provided at the + input terminal and - input terminal of the differential receiver 121, respectively, to block the DC component in the input signal. Therefore, the differential receiver 121 outputs a single-ended audio signal from the differential signal excluding the DC component of the signal output from the microphone unit 2 (see Figure 3).

[0025] The microcontroller 111 receives the signal (VDET1) from the microphone unit's + output terminal, including its DC component. That is, the microcontroller 111 monitors the signal (VDET1) from the microphone unit 2's + output terminal at predetermined time intervals, for example, via an analog-to-digital (AD) converter. Based on VDET1, the microcontroller 111 determines the connection status of the microphone unit 2 through the process illustrated in Figure 9 and subsequent diagrams.

[0026] Figure 8 also illustrates the differential receiver 121 included in the hands-free circuit 12 in the in-vehicle unit 1B illustrated in Figure 4. In the in-vehicle unit 1A of Figure 7, the microcontroller 111 monitors the signal (VDET1) at the + output terminal of the microphone unit 2 at predetermined time intervals via an analog-to-digital (AD) converter. In contrast, in the in-vehicle unit 1B of Figure 8, the microcontroller 111 monitors the signal (VDET2) at the - output terminal of the microphone unit 2 at predetermined time intervals, for example, via an analog-to-digital (AD) converter. The configuration of the in-vehicle unit 1B, excluding the configuration for monitoring VDET2, is the same as that of the in-vehicle unit 1A, so its explanation is omitted.

[0027] (A. Detected voltage in each connection state) (A1. When connected) Figure 9 illustrates the equivalent circuit for the DC signal of the in-vehicle unit 1A in Figure 7 or the in-vehicle unit 1B in Figure 8, with the microphone unit 2 connected. It can also be considered that Figure 9 represents the equivalent circuit when the input impedance between the + input terminal and the - input terminal of the in-vehicle unit 1A or 1B is sufficiently large compared to R1, R2, R3, and Zm. Furthermore, in Figures 7 and 8, the input impedance of the terminal where the microcontroller 111 detects VDET1 or VDET2 is assumed to be sufficiently large, and therefore the microcontroller 111 is omitted in Figure 9.

[0028] As shown in Figure 9, when the microphone unit 2 is properly connected to the in-vehicle unit 1A or 1B, the microcontroller 111 detects the + midpoint potential (Vb+) as VDET1. VDET1=Vb+ =Vcc*(Zm+R2+R3) / (Zm+R1+R2+R3) (Formula 1) Here, / represents division and * represents multiplication (the same applies below).

[0029] Furthermore, in the state shown in Figure 9, the microcontroller 111 detects the value obtained by dividing the midpoint potential (Vb-) by resistors R2 and R3 connected in series as VDET2. Also, in Figure 9, VDET2 is the value obtained by dividing the power supply voltage Vcc by the output impedance Zm of the microphone unit and resistor R3 in a series circuit of resistors R1 to R3. VDET2=Vcc*R3 / (Zm+R1+R2+R3) (Formula 2)

[0030] If R2 is absent, the microcontroller 111 detects the negative midpoint potential (Vb-) as VDET2. As described above, when the microphone unit 2 is properly connected to the in-vehicle unit 1A, the microcontroller 111 detects the positive midpoint potential (Vb+) as VDET1 from the positive output terminal of the microphone unit 2. Also, when the microphone unit 2 is properly connected to the in-vehicle unit 1B, the microcontroller 111 detects the value obtained by dividing the negative midpoint potential (Vb-) by resistors R2 and R3 as VDET2 from the negative output terminal of the microphone unit 2. However, if resistor R2=0, i.e., if resistor R2 is removed, VDET2 is the negative midpoint potential (Vb-) itself.

[0031] (A2. Not connected) Figure 10 illustrates the equivalent circuit for a DC signal in either the in-vehicle unit 1A in Figure 7 or the in-vehicle unit 1B in Figure 8 when the microphone unit 2 is not connected. It can also be considered that Figure 10 represents the equivalent circuit when the input impedance between the + input terminal and the - input terminal is sufficiently large compared to the resistors R1, R2, R3, and Zm in either the in-vehicle unit 1A in Figure 7 or the in-vehicle unit 1B in Figure 8.

[0032] If the microphone unit 2 is not connected to the in-vehicle unit 1A in Figure 7, VDET1 becomes the power supply voltage Vcc supplied through resistor R1. In other words, under normal connection conditions, the microcontroller 111 detects the signal from the + output terminal of the microphone unit 2 as VDET1. However, if the microphone unit 2 is not connected, VDET1 becomes the power supply voltage Vcc, as shown in Figure 10.

[0033] VDET1=Vcc (Formula 3) If the microphone unit 2 is not connected to the in-vehicle unit 1B in Figure 8, VDET2 will be at ground potential (GND, 0V) via resistor R3. In other words, under normal connection conditions, the microcontroller 111 detects the signal from the negative output terminal of the microphone unit 2 as VDET2. However, if the microphone unit 2 is not connected, VDET2 will be at ground potential, as shown in Figure 10. VDET2=GND(0V) (Formula 4)

[0034] (A3. Heavenly and Earthly Interconnections) Figure 11 is an equivalent circuit illustrating the values ​​of VDET1 and VDET2 when a sky fault or ground fault occurs in the in-vehicle unit 1A in Figure 7 or the in-vehicle unit 1B in Figure 8, with the microphone unit 2 connected. In Figure 11, the paths of sky faults and ground faults are illustrated with dotted lines.

[0035] In Figure 11, two types of overhead faults are illustrated. The first type, overhead fault 1, occurs when the + output terminal of microphone unit 2 is short-circuited to the power supply voltage Vcc. The second type, overhead fault 2, occurs when the - output terminal of microphone unit 2 is short-circuited to the power supply voltage Vcc. Furthermore, Figure 11 also illustrates two types of ground faults. The first type, ground fault 1, occurs when the - output terminal of microphone unit 2 is short-circuited to the ground potential. Furthermore, the second type, ground fault 2, is one in which the + output terminal of microphone unit 2 is short-circuited to ground potential.

[0036] (A31.Heaven 1) If a short circuit 1 occurs, the microcontroller 111 of the in-vehicle unit 1A in Figure 7 detects the power supply voltage Vcc as VDET1. VDET1=Vcc (formula 5) Therefore, in the configuration of the in-vehicle unit 1A shown in Figure 7, the microcontroller 111 detects the power supply voltage Vcc as the voltage at the VDET1=+ output terminal, whether the microphone unit 2 is not connected to the in-vehicle unit 1A (Figure 10) or a fault 1 occurs.

[0037] Furthermore, if a short circuit 1 occurs, the microcontroller 111 of the in-vehicle unit 1B in Figure 8 detects a voltage as VDET2 obtained by dividing the power supply voltage Vcc by resistor R3 in a series circuit of the microphone unit's output impedance Zm and resistors R2 and R3. That is, VDET2=Vcc*R3 / (Zm+R2+R3) (Formula 6) Therefore, the microcontroller 111 can determine that a fault 1 has occurred when VDET2 is greater than or equal to the third threshold voltage V3, which is higher than the value of VDET2 calculated by (Equation 2) and lower than the value calculated by (Equation 6). Also, when the resistance R2 = 0, VDET2 is the voltage at the - output terminal, so the microcontroller 111 can determine that a fault 1 has occurred when the voltage at the - output terminal is greater than or equal to the third threshold voltage V3. In this embodiment, a threshold voltage is used as an example of a threshold.

[0038] (A32.Heaven 2) If a short circuit 2 occurs, the microcontroller 111 of the in-vehicle unit 1A in Figure 7 detects the power supply voltage Vcc as VDET1. VDET1=Vcc (formula 7)

[0039] Therefore, in the configuration of the in-vehicle unit 1A shown in Figure 7, the microcontroller 111 detects the power supply voltage Vcc as VDET1 in both cases: when the microphone unit 2 is not connected to the in-vehicle unit 1A (Figure 10), and when fault 1 and fault 2 occur. In other words, in the configuration of the in-vehicle unit 1A shown in Figure 7, the microcontroller 111 cannot distinguish between unconnected, fault 1, and fault 2 even if it acquires only VDET1.

[0040] Furthermore, if a short circuit 2 occurs, the microcontroller 111 of the in-vehicle unit 1B in Figure 8 detects the voltage obtained by dividing the power supply voltage Vcc in series with resistors R2 and R3, with resistor R3 acting as VDET2. That is, VDET2=Vcc*R3 / (R2+R3) (Equation 8) That is the case.

[0041] Furthermore, when resistance R2=0, VDET2 is the voltage at the -output terminal, and VDET2=Vcc. That is, when R2=0, the microcontroller 111 can determine that a fault 1 has occurred when the voltage at the -output terminal becomes Vcc. Also, when R2=0, the microcontroller 111 can determine that a fault 2 has occurred when VDET2 becomes equal to or greater than the first threshold voltage V1, which is higher than the value of VDET2 at the time of connection calculated by (Equation 2) and less than Vcc.

[0042] (A33. Ground fault 1) When a ground fault 1 occurs, the microcontroller 111 of the in-vehicle unit 1A in Figure 7 detects a voltage as VDET1, which is the power supply voltage Vcc divided by the output impedance Zm in a series circuit of the output impedance Zm of the microphone unit 2 and the resistor R1. VDET1 = Vcc * Zm / (Zm + R1) (Equation 9) Therefore, the microcontroller 111 can determine that a ground fault 1 has occurred when VDET1 falls below the fourth threshold voltage V4, which is lower than the value of VDET1 calculated by (Equation 1) and higher than the value calculated by (Equation 9).

[0043] When a ground fault 1 occurs, the microcontroller 111 of the in-vehicle unit 1B in Figure 8 detects the ground potential as VDET2. VDET2=GND(0V) (Formula 10) Therefore, in the configuration of the in-vehicle unit 1B shown in Figure 8, the microcontroller 111 detects the ground potential as VDET2 in both cases: when the microphone unit 2 is not connected to the in-vehicle unit 1B (Figure 10) and when a ground fault 1 occurs.

[0044] (A34. Ground fault 2) When a ground fault 2 occurs, the microcontroller 111 of the in-vehicle unit 1A in Figure 7 detects the ground potential as VDET1. VDET1=GND(0V) (Formula 11) In other words, the microcontroller 111 can detect a ground fault 2 when VDET1 is less than or equal to the second threshold voltage V2, using the value of VDET1 calculated by (Equation 1), which is lower than the +midpoint potential (Vb+) and higher than the value of (Equation 11).

[0045] Furthermore, if a ground fault 2 occurs, the microcontroller 111 of the in-vehicle unit 1B in Figure 8 detects the ground potential as VDET2. VDET2=GND(0V) (Formula 12) Therefore, in the configuration of the in-vehicle unit 1B shown in Figure 8, the microcontroller 111 detects the ground potential as VDET2 in both cases: when the microphone unit 2 is not connected to the in-vehicle unit 1B (Figure 10), and when ground fault 1 or ground fault 2 occurs. In other words, in the configuration of the in-vehicle unit 1B shown in Figure 8, the microcontroller 111 cannot distinguish between unconnected, ground fault 1, and ground fault 2 even if it acquires only VDET2.

[0046] (B. Judgment Procedure) Figure 12 is a timing chart illustrating the changes in the values ​​of VDET1 and VDET2 detected by the microcontroller 111 when the connection status changes to disconnected, overhead fault 1, overhead fault 2, ground fault 1, and ground fault 2. However, Figure 12 illustrates the calculation results when Zm=R1=R3=100 ohms and R2=0 ohms. Here, by setting R2=0 ohms, i.e., eliminating R2, in the configuration of Figure 8, the in-vehicle unit 1B can measure the voltage at the negative output terminal of the microphone unit 2 as VDET2 and determine the connection status of the microphone unit 2.

[0047] (B1. Determined to be connected) First, when the microphone unit 2 is connected to the in-vehicle unit 1A, the voltage VDET1 detected by the microcontroller 111 from the + output terminal is as shown in (Equation 1) above. VDET1=Vb+ =Vcc*(Zm+R2+R3) / (Zm+R1+R2+R3) = 2 / 3Vcc

[0048] On the other hand, the voltage VDET2 detected by the microcontroller 111 from the negative output terminal is as shown in (Equation 2) above when the microphone unit 2 is connected to the in-vehicle unit 1B. VDET2=Vb- =Vcc*R3 / (Zm+R1+R2+R3) =Vcc / 3

[0049] (B2. Determined as not connected) When the microphone unit 2 changes from being connected to the in-vehicle unit 1A to being disconnected, the voltage VDET1 detected by the microcontroller 111 from the + output terminal is the power supply voltage Vcc, as shown in (Equation 3) above.

[0050] VDET1=Vcc Therefore, the microcontroller 111 can use a value higher than VDET1 = 2 / 3 * Vcc when connected, but smaller than Vcc, for example, 9 / 10 * Vcc, as the first threshold voltage V1. In other words, when the microcontroller 111 detects that VDET1 has changed from 2 / 3 * Vcc to a value greater than or equal to the first threshold voltage V1, it can determine that the microphone unit 2 has changed from being connected to the in-vehicle unit 1A to being disconnected.

[0051] On the other hand, when the microphone unit 2 changes from being connected to the in-vehicle unit 1B to being disconnected, the voltage VDET2 detected by the microcontroller 111 from the - output terminal is the ground potential, as shown in (Equation 4) above.

[0052] VDET2 = GND (0V) Therefore, the microcontroller 111 can use a value lower than VDET2 = Vcc / 3 when connected, and greater than the ground potential GND (0V), for example, Vcc / 10, as the second threshold voltage V2. In other words, when the microcontroller 111 detects that VDET2 has changed from Vcc / 3 to a value less than or equal to the second threshold voltage V2, it can determine that the microphone unit 2 has changed from being connected to the in-vehicle unit 1B to being disconnected.

[0053] (B3. Determination of Heavenly Intertwining) When the microphone unit 2 is connected to the in-vehicle unit 1B and then enters the state of air fault 1, the voltage VDET2 detected by the microcontroller 111 from the negative output terminal is as shown in (Equation 6) above. VDET2 = Vcc * R3 / (Zm + R2 + R3) =Vcc / 2 Also, since R2=0, VDET2 is the voltage at the negative output terminal.

[0054] When the microphone unit 2 is connected to the in-vehicle unit 1B and then enters the state of air fault 2, the voltage VDET2 detected by the microcontroller 111 from the negative output terminal is as shown in (Equation 8) above. VDET2 = Vcc * R3 / (R2 + R3) =Vcc Therefore, the microcontroller 111 can use a value that is higher than VDET2 = Vb - = Vcc / 3 when connected, and smaller than Vcc / 2 in the state of fault 1, for example, Vcc * 4 / 10, as the third threshold voltage V3. In other words, when the microcontroller 111 detects that VDET2 has changed from Vcc / 3 to a value greater than or equal to the third threshold voltage V3, it can determine that the microphone unit 2 has changed from being connected to the in-vehicle unit 1B to a state of fault as exemplified by faults 1 and 2.

[0055] (B4. Ground fault determination) When the microphone unit 2 is connected to the in-vehicle unit 1A and then a ground fault occurs, the voltage VDET1 detected by the microcontroller 111 from the + output terminal is as shown in (Equation 9) above. VDET1 = Vcc * Zm / (Zm + R1) =Vcc / 2

[0056] When the microphone unit 2 is connected to the in-vehicle unit 1A, and then a ground fault 2 occurs, the voltage VDET1 detected by the microcontroller 111 from the + output terminal is the ground potential, as shown in (Equation 11) above. That is, VDET1 = GND (0V) Therefore, the microcontroller 111 can use a value lower than VDET1=Vb+=2 / 3*Vcc when connected, and higher than VDET1=Vcc / 2 in the ground fault 1 state, for example, Vcc*6 / 10, as the fourth threshold voltage V4. In other words, when the microcontroller 111 detects that VDET1 has changed from 2 / 3*Vcc to a value less than or equal to the fourth threshold voltage V4, it can determine that the microphone unit 2 has changed from being connected to the in-vehicle unit 1A to a ground fault as exemplified by ground faults 1 and 2. Note that the fifth threshold voltage V5 to the eighth threshold voltage V8 in Figure 12 will be explained separately in Embodiment 2.

[0057] Figure 13 is another example of a timing chart illustrating the changes in VDET1 and VDET2 values ​​detected by the microcontroller 111 when the connection status changes to disconnected, fault 1, fault 2, ground fault 1, and ground fault 2. Here, Figure 13 illustrates the calculation results with Zm=R1=100 ohms and R2=R3=50 ohms. In the case of Figure 13, as in the case of Figure 12, the first threshold voltage V1 to the fourth threshold voltage V4 that detect changes in the values ​​of VDET1 and VDET2 can be set. Therefore, the microcontroller 111 can determine that the microphone unit 2 has gone from being connected to the in-vehicle unit 1B to disconnected, faulted, or grounded, as in the case of Figure 12. However, in the case of Figure 13, since R2 is present, the value of VDET2 measured by the microcontroller 111 of the in-vehicle unit 1B is not the voltage of the - output terminal, but the value of the voltage of the - output terminal measured through resistor R2.

[0058] (Processing procedure) Figure 14 is a flowchart illustrating the processing of the microcontroller 111 of the in-vehicle unit 1A or 1B. In this process, the microcontroller 111 measures the terminal voltage of the + output terminal or the - output terminal and determines whether the terminal voltage at the same terminal (+ output terminal or - output terminal) has deviated from the threshold multiple times in a row (N times) (S1, S2). That is, the microcontroller 111 samples the terminal voltage N times and determines whether the terminal voltage of the + output terminal or the - output terminal has deviated from the threshold in all N sampling results. The period during which N sampling is performed is an example of a predetermined period. However, the predetermined period may be, for example, the period during which N sampling is performed.

[0059] In the determination in S2, if the terminal voltage at the same terminal comes within the threshold range before it deviates from the threshold multiple times in a row (N times) (N in S2), the microcontroller 111 determines that the microphone unit 2 is connected to the in-vehicle unit 1A (or 1B) (S3). Therefore, the microcontroller 111 displays on the display device or light-emitting device of the in-vehicle unit 1A (or 1B) that the microphone unit 2 is properly connected (S4).

[0060] On the other hand, in the determination of S2, if the terminal voltage at the same terminal deviates from the threshold multiple times in a row (N times) (Y in S2), the microcontroller 111 determines that the microphone unit 2 is not properly connected to the in-vehicle unit 1A (or 1B) (S5). Here, N is an integer of 2 or more, and is set appropriately according to the state of the in-vehicle unit 1A (or 1B) and the microphone unit 2. Note that if the voltage deviates from the threshold multiple times in a row (N times), it can also be said that the deviated state continues for a predetermined period of time.

[0061] For example, if VDET1 in the in-vehicle unit 1A is confirmed to be above the first threshold voltage V1 for N consecutive times, the microcontroller 111 determines that the microphone unit 2 is not connected. Similarly, if VDET2 in the in-vehicle unit 1B is confirmed to be below the second threshold voltage V2 for N consecutive times, the microcontroller 111 determines that the microphone unit 2 is not connected. Likewise, if VDET1 in the in-vehicle unit 1A is confirmed to be below the fourth threshold voltage V4 for N consecutive times, the microcontroller 111 detects the occurrence of a ground fault. Furthermore, if VDET2 in the in-vehicle unit 1A is confirmed to be above the third threshold voltage V3 for N consecutive times, the microcontroller 111 The microcontroller 111 then detects the occurrence of a wind rupture. The microcontroller 111 then displays the result of the determination in S5 on the display device or light-emitting device of the in-vehicle unit 1A (or 1B) (S6).

[0062] <Comparative Example 2> Figure 15 is a flowchart illustrating the processing according to Comparative Example 2. In Embodiment 1 described above, the microcontroller 111 measures the terminal voltage from the + output terminal or the - output terminal and determines whether the terminal voltage at the same terminal (+ output terminal or - output terminal) deviates from the threshold multiple times in a row (N times). The processing in Comparative Example 2 detects whether the result of a single measurement deviates from the threshold (S501), and based on that detection result, determines whether the microphone unit 2 is connected to the in-vehicle unit 1A (or 1B).

[0063] In other words, if the terminal voltage at the same terminal (+ output terminal or - output terminal) is within the threshold range (Y in S501), the process of Comparative Example 2 determines that the microphone unit 2 is connected to the in-vehicle unit 1A (or 1B) (S502). On the other hand, if the terminal voltage at the same terminal (+ output terminal or - output terminal) is not within the threshold range (N in S501), the process of Comparative Example 2 determines that the microphone unit 2 is not connected to the in-vehicle unit 1A (or 1B) (S503).

[0064] Figure 16 illustrates the problems in the processing of Comparative Example 2. Figure 16 illustrates the changes in the voltage VDET1 at the + output terminal and the voltage VDET2 at the - output terminal measured by the microcontroller 111. In Figure 16, VDET1 and VDET2 fluctuate around the midpoint potential of the + terminal and the midpoint potential of the - terminal, respectively, which are represented by dashed lines. Furthermore, the threshold ranges for the + terminal and the - terminal, used to determine whether the microphone unit 2 is properly connected to the in-vehicle unit 1A (or 1B), are each exemplified by the ranges enclosed by two dashed lines. In this state, if excessive sound pressure is applied to the microphone unit 2, the amplitude of the output signal of the microphone unit 2 may exceed (fall outside) the threshold range. In this example, at sampling at timings T1 and T2, exemplified by dotted circles, VDET1 and VDET2 are outside the threshold ranges for the + terminal and the - terminal, respectively. Therefore, when data like that shown in Figure 16 is sampled, in the processing of Comparative Example 2, the microcontroller 111 determines that the microphone unit 2 is not properly connected to the in-vehicle unit 1A (or 1B) and displays "Not connected," "Air fault," "Ground fault," etc. In other words, even though the microphone unit 2 is properly connected to the in-vehicle unit 1A (or 1B), it may incorrectly detect "Not connected," "Air fault," "Ground fault," etc.

[0065] (Effects of Embodiment 1) As described above, in the processing of Embodiment 1, the microcontroller 111 does not determine that there is a connection abnormality unless the terminal voltage (+ output terminal or - output terminal) at the same terminal does not deviate from the threshold for multiple consecutive times (N times). Here, a connection abnormality means that the microphone unit 2 has gone from being connected to the in-vehicle unit 1A to being disconnected, or that a ceiling fault or ground fault has occurred. And, in the data of Figure 16, for example, if an integer of 3 or more is set as N, the microcontroller 111 will not make a misjudgment of the data of Figure 16. Therefore, the microcontroller 111 can reliably determine that the microphone unit 2 is not properly connected to the in-vehicle unit 1A (or 1B) by monitoring either the output terminal voltage VDET1 or the - output terminal voltage VDET2. For example, as illustrated in Figure 16, even if a signal with a temporarily large amplitude is detected, it is possible to suppress the microcontroller 111 from misdetecting disconnection, ceiling fault, or ground fault.

[0066] Furthermore, in the case of the in-vehicle unit 1B, the monitored signal line is the one connected to the output terminal which is biased with the negative power supply voltage (ground potential GND), and the microcontroller 111 can detect a fault when the measured voltage is greater than or equal to the third threshold voltage V3. In addition, in the case of the in-vehicle unit 1A, the monitored signal line is the one connected to the + output terminal which is biased with the positive power supply voltage (Vcc). This is a signal line connected to the power terminal, and the microcontroller 111 can detect a ground fault when the measured voltage is below the fourth threshold voltage V4.

[0067] <Embodiment 2> Figure 17 is a diagram illustrating the configuration of the in-vehicle unit 1C according to Embodiment 2. In the in-vehicle unit 1C, the microcontroller 111 monitors both the voltage VDET1 at the + output terminal and the voltage VDET2 at the - output terminal. The configuration and operation of the in-vehicle unit 1C, other than the configuration in which the microcontroller 111 monitors both VDET1 and voltage VDET2, are the same as those of the in-vehicle unit 1A or 1B of Embodiment 1. Therefore, for the configuration of the in-vehicle unit 1C according to Embodiment 2 that is the same as that of the in-vehicle unit 1A or 1B of Embodiment 1, the same reference numerals are used and their descriptions are omitted.

[0068] In Embodiment 1, the microcontroller 111 of the in-vehicle unit 1A monitors VDET1, and the microcontroller 111 of the in-vehicle unit 1B monitors VDET2. On the other hand, in Embodiment 2, the microcontroller 111 of the in-vehicle unit 1C monitors both VDET1 and voltage VDET2. However, when disconnection, sky fault 1, sky fault 2, ground fault 1, and ground fault 2 occur, the changes in the VDET1 and VDET2 signals in the in-vehicle unit 1C are the same as those in the in-vehicle unit 1A and VDET2 in the in-vehicle unit 1B of Embodiment 1.

[0069] Therefore, the determination method of the microcontroller 111 in the in-vehicle unit 1C will be explained with reference to Figure 12. Also, as already mentioned, Figure 12 shows an example of the calculation result when Zm=R1=R3=100 ohms and R2=0 ohms.

[0070] (C1. Determined to be connected) As described above, when the microphone unit 2 is connected to the in-vehicle unit 1C, the voltage VDET1 detected by the microcontroller 111 from the + output terminal is as shown in (Equation 1) above. VDET1=Vb+ =Vcc*(Z+R2+R3) / (Z+R1+R2+R3) = 2 / 3Vcc

[0071] On the other hand, when the microphone unit 2 is connected to the in-vehicle unit 1C, the voltage VDET2 detected by the microcontroller 111 from the - output terminal is as shown in (Equation 2) above. VDET2 = Vcc * R3 / (Z + R1 + R2 + R3) =Vcc / 3

[0072] (C2. Determined as not connected) When the microphone unit 2 changes from being connected to the in-vehicle unit 1A to being disconnected, the voltage VDET1 detected by the microcontroller 111 from the + output terminal is the power supply voltage Vcc, as described above. VDET1=Vcc

[0073] Therefore, the microcontroller 111 can use a value that is higher than VDET1 = Vcc * 2 / 3 when connected, and lower than the power supply voltage Vcc, for example, Vcc 9 / 10, as the fifth threshold voltage V5. That is, when the microcontroller 111 detects that VDET1 has changed from Vcc 2 / 3, which is the connected VDET1, to a value equal to or greater than the fifth threshold voltage V5, it can determine that the microphone unit 2 has changed from a state where it is connected to the in-vehicle unit 1C to a state where it is not connected. The fifth threshold voltage V5 may be the same value as the first threshold voltage V1 in Embodiment 1.

[0074] On the other hand, when the microphone unit 2 changes from being connected to the in-vehicle unit 1B to being disconnected, the voltage VDET2 detected by the microcontroller 111 from the - output terminal is the ground potential, as shown in (Equation 4) above. VDET2 = GND (0V)

[0075] Therefore, the microcontroller 111 can use a value lower than VDET2 = Vcc / 3 when connected and greater than the ground potential GND (0V) as the seventh threshold voltage V7, for example, Vcc / 10. That is, the microcontroller 111 can use VDET2 = Vcc / 3 when connected. 3 Therefore, when it is detected that the value has changed to a value below the seventh threshold voltage V7, it can be determined that the microphone unit 2 has changed from being connected to the in-vehicle unit 1C to being disconnected. The seventh threshold voltage V7 may be the same value as the second threshold voltage V2.

[0076] (C3. Determination of the entanglement) When the microphone unit 2 is connected to the in-vehicle unit 1B and then enters the state of air fault 1, the voltage VDET2 detected by the microcontroller 111 from the negative output terminal is as shown in (Equation 6) above. VDET2 = VDET2 = Vcc * R3 / (Zm + R2 + R3) =Vcc / 2 That is the case.

[0077] Furthermore, when the microphone unit 2 is connected to the in-vehicle unit 1B and then enters the state of airtightness 2, the voltage VDET2 detected by the microcontroller 111 from the negative output terminal is as shown in (Equation 8) above. VDET2 = Vcc * R3 / (R2 + R3) =Vcc

[0078] On the other hand, when the microphone unit 2 is connected to the in-vehicle unit 1C, and then enters the state of fault 1 or fault 2, the voltage VDET1 detected by the microcontroller 111 from the + output terminal is the power supply voltage Vcc, as shown in (Equation 5) and (Equation 7) above. Therefore, the microcontroller 111 sets the fifth threshold voltage V5, and VDET2 = Vcc / 3 A value higher than and smaller than Vcc, for example, Vcc*9 / 10, can be used. That is, the microcontroller 111 can use VDET2 when VDET2 is Vcc / 3 Therefore, when it is detected that the value has changed to a value greater than or equal to the fifth threshold voltage V5, it can be determined that the microphone unit 2 has changed from being connected to the in-vehicle unit 1C to a fault as exemplified by fault 2. The fifth threshold voltage V5 may be the same value as the first threshold voltage V1.

[0079] Also, VDET2's sky rift 1 To detect this, the microcontroller 111 can use a sixth threshold voltage V6 that is higher than VDET2 = Vcc / 3 when connected and lower than Vcc / 2 when there is a rift, for example, Vcc*4 / 10. That is, the microcontroller 111 can detect when VDET2 is Vcc / 3 When it is detected that the sixth threshold voltage has changed to a value greater than or equal to V6, the microphone unit 2 is connected to the in-vehicle unit 1C, and a fault occurs. 1 It can be determined that it has become that.

[0080] From the above, if both VDET1 and VDET2 are above the fifth threshold voltage V5, the microcontroller 111 will cause a short circuit in the connection of the microphone unit 2. 2 It can be determined that a fault has occurred. Alternatively, if one of VDET1 and VDET2 (VDET1) is above the fifth threshold voltage V5 and the other (VDET2) is above the sixth threshold voltage V6, the microcontroller 111 determines that a fault has occurred in the connection of the microphone unit 2. 1 It can be determined that this has occurred.

[0081] (C4. Ground fault determination) When the microphone unit 2 is connected to the in-vehicle unit 1C and then a ground fault occurs, the voltage VDET1 detected by the microcontroller 111 from the + output terminal is as shown in (Equation 9) above. VDET1 = Vcc * Z / (Z + R1) =Vcc / 2

[0082] When the microphone unit 2 is connected to the in-vehicle unit 1A and then a ground fault 2 occurs, the voltage VDET1 detected by the microcontroller 111 from the + output terminal is the ground potential, as shown in (Equation 11) above. VDET1 = GND (0V) On the other hand, when the microphone unit 2 is connected to the in-vehicle unit 1C, a ground fault occurs. or Ground fault 2 When this state occurs, the voltage VDET2 detected by the microcontroller 111 from the - output terminal is the ground potential, as shown in (Equation 10) and (Equation 12) above. As the seventh threshold voltage V7, VDET2 = Vcc / 3 A value lower than and higher than the ground potential, for example, Vcc / 10, can be used. That is, when both VDET1 and VDET2 are less than or equal to the seventh threshold voltage V7, the microcontroller 111 is not detecting a ground fault. 2 It can be determined that it has become that.

[0083] Furthermore, as the eighth threshold voltage V8 for the microcontroller 111 to detect ground fault 1 using VDET1, a value lower than VDET1 = Vcc * 2 / 3 when connected, and higher than Vcc / 2, such as Vcc * 6 / 10, can be used. In other words, when the microcontroller 111 detects that VDET1 has changed from 2 / 3 * Vcc to a value less than or equal to the eighth threshold voltage V8, it can determine that ground fault 1 has occurred from the state in which the microphone unit 2 was connected to the in-vehicle unit 1C. The eighth threshold voltage V8 may also be the same value as the fourth threshold voltage V4.

[0084] From the above, both VDET1 and VDET2 are at the seventh threshold voltage V 7 In the following cases, the microcontroller 111 will cause a ground fault in the connection of the microphone unit 2. 2It can be determined that a ground fault has occurred. Alternatively, if one of VDET1 and VDET2 (VDET2) is below the seventh threshold voltage V7 and the other (VDET1) is below the eighth threshold voltage V8, the microcontroller 111 determines that a ground fault has occurred in the connection of the microphone unit 2. 1 It can be determined that this has occurred. Here, the eighth threshold voltage V8 is higher than the seventh threshold voltage V7.

[0085] Figure 13, like Figure 12, is a timing chart illustrating the changes in VDET1 and VDET2 values ​​detected by the microcontroller 111 when the connection status changes to disconnected, ceiling fault 1, ceiling fault 2, ground fault 1, and ground fault 2. However, the processing of the microcontroller 111 is the same as that described in Figure 12, so that explanation is omitted.

[0086] (Processing procedure) Figure 18 is a flowchart illustrating the processing of the in-vehicle unit 1C in Embodiment 2. In Embodiment 2, the microcontroller 111 determines the connection status between the microphone unit 2 and the in-vehicle unit 1C by monitoring both VDET1 and VDET2.

[0087] In this process, the microcontroller 111 measures both the voltage VDET1 from the + output terminal and the voltage VDET2 from the - output terminal (S11). The microcontroller 111 then determines whether the voltage VDET1 from the + output terminal is greater than or equal to the first threshold voltage V1, and the voltage VDET2 from the - output terminal is less than or equal to the second threshold voltage V2 (S12).

[0088] In the S12 determination, if VDET1 is greater than or equal to the first threshold voltage V1 and voltage VDET2 is less than or equal to the second threshold voltage V2 (Y in S12), the microcontroller 111 determines that the microphone unit 2 is not connected to the in-vehicle unit 1C. The microcontroller 111 then displays on the display device or light-emitting device of the in-vehicle unit 1C that the microphone unit 2 is not connected.

[0089] In the determination in S12, if VDET1 is not equal to or greater than the first threshold voltage V1, or if voltage VDET2 is not equal to or less than the second threshold voltage V2, the microcontroller 111 proceeds to S14. Then, the microcontroller 111 determines whether both VDET1 and VDET2 are equal to or greater than the fifth threshold voltage V5. Alternatively, the microcontroller 111 determines whether one of VDET1 and VDET2 (V It is determined that DET1) is greater than or equal to the fifth threshold voltage V5, and the other (VDET2) is greater than or equal to the sixth threshold voltage V6 (S14). Here, the sixth threshold voltage V6 is lower than the fifth threshold voltage V5.

[0090] If the determination in S14 is Y, the microcontroller 111 determines that a ground fault has occurred. Then, the microcontroller 111 displays that a ground fault has occurred on the display device or light-emitting device of the in-vehicle unit 1C (S15).

[0091] If the result of S14 is N, the microcontroller 111 proceeds to S16. The microcontroller 111 then determines whether both VDET1 and VDET2 are less than or equal to the seventh threshold voltage of 7. Alternatively, the microcontroller 111 determines that one of VDET1 and VDET2 (VDET2) is less than or equal to the seventh threshold voltage V7, and the other (VDET1) is less than or equal to the eighth threshold voltage V8 (S16). Here, the eighth threshold voltage V8 is a higher value than the seventh threshold voltage V7.

[0092] If the determination in S16 is Y, the microcontroller 111 determines that a ground fault has occurred. The microcontroller 111 then displays the fact that a ground fault has occurred on the display device or light-emitting device of the in-vehicle unit 1C (S17).

[0093] If the result of S16 is N, the microcontroller 111 determines that the microphone unit 2 is properly connected to the in-vehicle unit 1C. The microcontroller 111 then displays on the display device or indicator lamp of the in-vehicle unit 1C that a proper connection is maintained (S18).

[0094] (Effects of Embodiment 2) As described above, the in-vehicle unit 1C of Embodiment 2 measures the voltage of both of a pair of differential signal lines connected to the + output terminal and the - output terminal. The in-vehicle unit 1C detects that the microphone unit 2 is not connected to the in-vehicle unit 1C when the voltage of one of the pair of differential signal lines is equal to or greater than the fifth threshold voltage V5 and the voltage of the other is equal to or less than the seventh threshold voltage V7. Therefore, by monitoring both the + output terminal and the - output terminal, the in-vehicle unit 1C can more reliably and accurately detect that the microphone unit 2 is not connected to the in-vehicle unit 1C and display this information on a display device or the like.

[0095] Furthermore, the in-vehicle unit 1C of Embodiment 2 determines that the microphone unit 2 is in a short circuit when both of the pair of differential signal lines connected to the + output terminal and the - output terminal are at or above the fifth threshold voltage V5. Alternatively, the in-vehicle unit 1C determines whether one of the pair of differential signal lines connected to the + output terminal and the - output terminal (+ output terminal, VDTE1) is at or above the fifth threshold voltage V5. In addition, the in-vehicle unit 1C determines that the microphone unit 2 is in a short circuit when the other (- output terminal, VDET2) is at or above the sixth threshold voltage V6, which is lower than the fifth threshold voltage V5. Therefore, by monitoring both the + output terminal and the - output terminal, the in-vehicle unit 1C can more reliably and accurately detect a short circuit in the microphone unit 2 and display it on a display device or the like.

[0096] Furthermore, the in-vehicle unit 1C determines that the microphone unit 2 is grounded when both of the pair of differential signal lines connected to the + output terminal and the - output terminal are below the seventh threshold voltage V7. Alternatively, the in-vehicle unit 1C determines that the microphone unit 2 is grounded when one of the lines (- output terminal, VDTE2) is below the seventh threshold voltage V7 and the other line (+ output terminal, VDTE1) is below the eighth threshold voltage V8, which is higher than the seventh threshold voltage V7. Therefore, by monitoring both the + output terminal and the - output terminal, the in-vehicle unit 1C can more reliably and accurately detect ground faults in the microphone unit 2 and display them on a display device or the like.

[0097] (modified version) In Figure 18, the microcontroller 111 monitors both VDET1 and VDET2. The connection status between the microphone unit 2 and the in-vehicle unit 1C is determined by a single detection. However, in Embodiment 2, as in Figure 14 of Embodiment 1, the microcontroller 111 of the in-vehicle unit 1C may measure the terminal voltage N times in a row and determine if the threshold is exceeded N times in a row. That is, the determinations in S12, S14, and S16 in Figure 18 may be performed N times in a row, and if the same determination result is obtained N times in a row, determination Y may be performed. By performing such N consecutive determinations in S12, S14, and S16 in Figure 18, the microcontroller 111 can more reliably determine disconnection, ceiling fault, and ground fault.

[0098] <Embodiment 3> Figure 19 is a diagram illustrating the configuration of the in-vehicle unit 1D according to Embodiment 3. The in-vehicle unit 1D has a configuration in which an impedance Z1 is connected in parallel to the microphone unit 2 between the + connection terminal and the - connection terminal, as in the in-vehicle unit 1C of Embodiment 2. In Embodiment 3, as in Embodiments 1 and 2, the microphone unit 2 is assumed to have an output impedance Zm. However, the output impedance Zm of the microphone unit 2 is assumed to be much larger than the impedance Z1 of the in-vehicle unit 1D. In this case, regardless of whether the microphone unit 2 is connected to the in-vehicle unit 1D or not, the voltages VDET1 and VDET2 detected by the microcontroller 111 will be as follows (Equation 1A) and (Equation 2A), similar to (Equation 1) and (Equation 2) in Embodiment 1.

[0099] VDET1=Vb+ =Vcc*(Z1+R2+R3) / (Z1+R1+R2+R3) (Formula 1A) VDET2=Vcc*R3 / (Z1+R1+R2+R3) (Formula 2A) In other words, in the in-vehicle unit 1D, VDET1 is at the positive midpoint potential (Vb+) regardless of whether the microphone unit 2 is connected or not. Also, in the in-vehicle unit 1D, VDET2 is the value obtained by dividing the negative midpoint potential (Vb-) by resistor R3 in the series resistance of R2 and R3. Furthermore, when resistor R2=0, VDET2 becomes the negative midpoint potential (Vb-).

[0100] In the in-vehicle unit 1D, the microcontroller 111 cannot determine whether the microphone unit 2 is connected or not based solely on the DC component of the signals from VDET1 and VDET2. Therefore, the microcontroller 111 may determine that the microphone unit 2 is connected, for example, if the signal level of the sound output from the microphone unit 2 is above a reference value. On the other hand, regarding ceiling faults and ground faults, the microcontroller 111 can determine them in the in-vehicle unit 1D in the same way as in Embodiments 1 and 2.

[0101] In embodiments 1 to 3 described above, a circuit including a microcontroller 111 was exemplified as the connection detection circuit 11. However, the connection detection circuit 11 is not limited to a circuit including a microcontroller 111. That is, the connection detection circuit 11 can also be realized with simple hardware that does not rely on a computer program. For example, a circuit combining a comparator and a counter can also detect when the terminal voltage (+ output terminal or - output terminal) deviates from the threshold multiple times in a row (N times). As the comparator, for example, an operational amplifier (OP amp) can be used. Furthermore, a circuit that compares each terminal of a microphone (+ output terminal or - output terminal) with a threshold can also realize the same function as the connection detection circuit 11 in embodiments 1 to 3.

[0102] <Examples of application> Embodiments 1 to 3 described above illustrate the processing of the microcontroller 111 to determine the connection status between the in-vehicle unit 1A to 1D and the microphone unit 2. However, the application of such processing is not limited to the in-vehicle unit 1A, etc. For example, the processing of the microcontroller 111 described above can be applied to various information processing devices instead of the in-vehicle unit 1A, etc. For example, various voice control systems, etc. The processing of the microcontroller 111 can be applied to determine the connection status between the device equipped with active noise cancellation, automatic volume control, etc., and the microphone unit 2.

[0103] <Computer-readable recording medium> A program that enables a computer or other machine or device (hereinafter referred to as "computer, etc.") to perform any of the above functions can be recorded on a recording medium that the computer, etc. can read. By having the computer, etc. read and execute the program on this recording medium, it can be made to provide that function.

[0104] Here, a recording medium that can be read by a computer refers to a recording medium that stores information such as data and programs through electrical, magnetic, optical, mechanical, or chemical means and can be read by a computer. Examples of such recording media that can be removed from a computer include flexible disks, magneto-optical disks, CD-ROMs, CD-R / Ws, DVDs, Blu-ray discs, DATs, 8mm tapes, and memory cards such as flash memory. In addition, recording media that are fixed to a computer include hard disks and ROMs (read-only memory). Furthermore, SSDs (Solid State Drives) can also be used as a recording medium that can be removed from a computer. It can also be used as a recording medium fixed to a surface, etc. [Explanation of Symbols]

[0105] 1, 1A, 1B, 1C, 1D Onboard equipment 2 Microphone Units 11. Connection detection circuit 12. Hands-free circuit 13 Power circuit 21 Sound detection unit 22 Differential Drivers 23, 24 Capacitors 111 Microcontroller 121 Differential Receiver

Claims

1. A detection circuit for detecting the connection status of a microphone powered by superimposing a power supply voltage on a pair of differential signal lines, wherein the pair of differential signal lines consist of a first signal line biased by the positive power supply voltage via a first resistor and a second signal line biased by the negative power supply voltage via a second resistor. The voltages of both of the pair of differential signal lines are measured, and the disconnection of the microphone is detected when the voltage of the first differential signal line is greater than or equal to a first threshold (V1) and the voltage of the second signal line is less than or equal to a second threshold (V2). When the voltages of both the first signal line and the second signal line are greater than or equal to the fifth threshold (V5), a short circuit in the second signal line is detected. When the voltage of the first signal line is greater than or equal to the fifth threshold (V5), and the voltage of the second signal line is lower than the fifth threshold (V5) and greater than or equal to the sixth threshold (V6), a void in the first signal line is detected. Detection circuit.

2. A detection circuit for detecting the connection status of a microphone powered by superimposing a power supply voltage on a pair of differential signal lines, wherein the pair of differential signal lines consist of a first signal line biased by the positive power supply voltage via a first resistor and a second signal line biased by the negative power supply voltage via a second resistor. The voltages of both of the pair of differential signal lines are measured, and the disconnection of the microphone is detected when the voltage of the first differential signal line is greater than or equal to a first threshold (V1) and the voltage of the second signal line is less than or equal to a second threshold (V2). When the voltages of both the first signal line and the second signal line are below the seventh threshold (V7), a ground fault in the first signal line is detected. A ground fault in the second signal line is detected when the voltage of the second signal line is less than or equal to the seventh threshold (V7), and the voltage of the first signal line is higher than the seventh threshold (V7) and less than or equal to the eighth threshold (V8). Detection circuit.

3. The first threshold (V1) is determined by the microphone's connection to the first signal line and the second signal line. The value is higher than the connection voltage of the first signal line when it is connected to the line, and lower than the positive power supply voltage. The second threshold (V2) is lower than the connection voltage of the second signal line when the microphone is connected to the first signal line and the second signal line, and is greater than the negative power supply voltage. The fifth threshold (V5) is a value that is higher than the connection voltage of the second signal line when the microphone is connected to the first signal line and the second signal line, and lower than the positive power supply voltage. The detection circuit according to claim 1, wherein the sixth threshold (V6) is higher than the connection voltage of the second signal line when the microphone is connected to the first signal line and the second signal line, and lower than the detection voltage of the second signal line when the first signal line is in a junction.

4. The first threshold (V1) is a value that is higher than the connection voltage of the first signal line when the microphone is connected to the first signal line and the second signal line, and lower than the positive power supply voltage. The second threshold (V2) is lower than the connection voltage of the second signal line when the microphone is connected to the first signal line and the second signal line, and is greater than the negative power supply voltage. The seventh threshold (V7) is a value that is lower than the connection voltage of the second signal line when the microphone is connected to the first signal line and the second signal line, and is greater than the negative power supply voltage. The detection circuit according to claim 2, wherein the eighth threshold (V8) is lower than the connection voltage of the first signal line when the microphone is connected to the first signal line and the second signal line, and greater than the detection voltage of the first signal line when the second signal line is ground faulted.

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