JPS5830274Y2 - Cassette tape end detection device - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a cassette tape end detection device.

Generally, a cassette tape used in a cassette tape recorder has a transparent leader tape (section) connected to an end of an opaque magnetic tape (section).

In order to detect the end of the magnetic tape (for reversing the running direction of the tape or automatically stopping the tape), the optical path from the light source to the light receiving element is blocked by the magnetic tape, and the amount of light received by the light receiving element is adjusted between the magnetic tape and the reader. It is known that the magnetic tape and the leader tape are distinguished from each other by the difference in transparency from the tape.

Also known is a device in which the electric signal from the light receiving element is differentiated so that the light receiving element detects the joint between the magnetic tape and the leader tape.

By the way, some of the above-mentioned leader tapes have various symbols (letters or patterns) attached to them, and if the amount of light received by the light-receiving element decreases due to these symbols, it is impossible to distinguish this decrease from that caused by the magnetic tape. An end angle detection signal is erroneously output at the end of the symbol on the leader tape.

The present invention prevents the output of an erroneous termination detection signal using the above-mentioned symbol, and as shown in Fig. 1, a phototransistor, etc. The optical path leading to the light receiving element 2 is blocked by a well-known cassette tape 3,
The electrical signal output from the light emitting element 2 is differentiated by the differentiating circuit 4, the rising edge of the output waveform of the differentiating circuit 4 is detected by the detecting circuit, and one input of the AND gate 6 is set to "1" at the rising edge. It is configured to do.

The detection circuit can be constructed of well-known means such as a transistor or diode that is forward biased by the rising edge of the output waveform.

The rising edge of the output waveform is a state in which relatively weak light is hitting the light receiving element 2 (or a state in which no light is hitting it at all).
, that is, from a state where the symbol part of the magnetic tape section or the leader tape section of the tape 3 is interposed between the light source 1 and the light receiving element 2, to a state where relatively strong light hits the light receiving element 2, that is, the state where the light source 1 and the light receiving element 2 This occurs when the state changes to a state where the leader part (transparent part) of the tape 3 is interposed between the light receiving element 2 and the light receiving element 2 .

Therefore, the rising edge of the above output waveform occurs at the end of the magnetic tape section if it is a joint from the magnetic tape section to the leader tape section, but it occurs at the end of the magnetic tape section from the symbol section of the leader tape section to the transparent section of the leader tape section. If so, it is not the end of the magnetic tape section.

A detection circuit 7 detects the fall of the output waveform from the differentiating circuit 4 and triggers a temporary holding circuit 8 made of a mono-multivibrator.

The detection circuit 7 can be constructed in a well-known manner using a transistor or a diode that is forward biased by the above-mentioned fall.

The fall occurs when the light receiving element 2 is exposed to relatively strong light, that is, the leader tape part (transparent) of the tape 3 is interposed between the light source 1 and the light receiving element 2. When the state changes to a state where the light is weak (or no longer shines at all), that is, the symbol part of the tape part or the magnetic tape part is interposed between the light source 1 and the light receiving element 2. arise.

The holding circuit 8 is operated for a predetermined period of time after being triggered by the output of the detection circuit 7, i.e., sufficient for the normal symbol part of the above-mentioned tape to pass between the light source 1 and the light receiving element 2. It has a hold time that causes the output to reverse over time.

An inverter 9 inverts the output of the holding circuit 8 and supplies it to the other input of the AND gate 6.

In the end detection device having the above configuration, as shown in FIG.
A falling signal shown as B is obtained from the detection circuit 7 at the beginning of , and a rising signal shown as C is obtained from the detection circuit 5 at the end of the symbol portion 11 and the end of the magnetic tape section 12 .

The output of the holding circuit 7 is inverted by the falling signal B for a predetermined time τ as shown in D, and this output is inverted as shown in E by the inverter 9 and supplied to the AND gate 6.

The predetermined period τ is set to be sufficiently longer than the passage time T1 of the symbol portion 11 and sufficiently shorter than the passage time T2 of the magnetic tape section 12.

Therefore, the rising edge (nJ
) is supplied to the AND gate 6, since rOJ is supplied from the inverter 9 to the AND gate,
The output of the AND gate 6 becomes rOJ as shown in FIG. 2F, and no termination detection signal is obtained.

On the other hand, a rising edge ("
1) is supplied to the AND gate 6, the AND gate is supplied with "1" from the inverter 9, so the output of the AND gate 6 is "1" as shown in FIG. 2F.
Then, a termination detection signal is obtained.

FIG. 3 shows another embodiment, in which 13 is an infrared light emitting diode, 14 is a phototransistor, and 15 is a tape interposed in the optical path between the diode 13 and the transistor 4.

Reference numeral 16 denotes a transistor that outputs a termination detection signal from a terminal 17, and when this transistor is turned off, the above detection signal is obtained.

This transistor 16 is biased to be turned on by the voltage divided by resistors R1 and R2.

Further, the transistor 4 is turned on only in the transparent portion of the leader tape portion of the tape 15, and turned off only in the symbol portion of the magnetic tape portion and the leader tape portion.

Therefore, in the off state of the transistor 14 where light is blocked by the magnetic tape portion, the capacitor C1 is charged via the resistor R3, and the capacitor C2 is charged via the resistor R3 and the base-emitter of the transistor 16.

When the large capacity capacitor C1 is sufficiently charged, the small capacity capacitor C2 can also be sufficiently charged, and the potential difference between both ends of the capacitor C2 becomes sufficiently large.

In this state, the transparent part of the leader tape part of the tape 15 passes between the diode 13 and the transistor 4, and when the transistor 14 is turned on, one end of the capacitor C2 becomes approximately ground potential, and the other end of the capacitor C2 is connected. The dividing point between the resistors R1 and R2 becomes a negative potential, turning off the transistor 16, and a termination detection signal is obtained at the terminal 11.

On the other hand, when the optical path is blocked by the symbol part of the leader tape part and the transistor 4 is turned off, the period in which the transistor 14 is off is short because the distance of the symbol part is short, and during this short period, the light is transmitted through the resistor R3. Due to the current, capacitor C1 is not sufficiently charged, and capacitor C
The potential difference between both ends of 2 is also small.

Therefore, even if the transistor 4 is turned on by the transparent part after the above-mentioned symbol part is turned on, and one end of the capacitor C2 becomes the ground potential, the difference in potential between both ends of the capacitor C2 is small, so the dividing point between the resistors R and R2 is That is, the drop in the base voltage of transistor 16 is small and does not drop until transistor 16 is turned off.

As mentioned above, even in the case of FIG. 3, if the off period of the transistor 14 is shorter than the predetermined period, the charging of the capacitor C1 is insufficient, and even if the transistor 14 is turned on, the transistor 6 is turned off. That is, output of the termination detection signal is prevented.

The present invention is as described above, and in the case of the above-mentioned symbol etc. in which the substantially opaque portion is short, the output of the false termination detection signal is prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a time chart showing the operation of FIG. 1, and FIG. 3 is a circuit diagram showing another embodiment. 1... Light source, 2... Light receiving element.

Claims (1)

[Scope of utility model registration request] The optical path from the light source to the light-receiving element is blocked by a cassette tape, and after the light-receiving element detects that relatively weak light is hitting the light-receiving element, it is detected that the light reaching the light-receiving element becomes relatively strong. in which a termination detection signal is output when the light receiving element detects relatively strong light, and then only for a predetermined period after relatively weak light is detected by the light receiving element. A cassette tape end detection device comprising means for preventing output of the end detection signal.