JPS599425Y2 - Tape end detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a tape end detection circuit that magnetically detects the end of a tape.

In order to detect the end of the tape, most video tape recorders have conductive foil such as aluminum foil placed at the beginning and end of the magnetic tape, and a coil element (tape sensor) is placed on the tape surface. The end of the tape is detected by detecting the contact of the coil element with the aluminum foil as a decrease in the Q value of the coil element, and the running of the tape is stopped.

Figure 1 shows a conventional circuit, in which a tape sensor L0 and a first capacitor G form a parallel tuned circuit, and the first and second resistors R
By applying the divided voltages of 1 and R2 and the resonance of the parallel tuned circuit, the amplifier 1 that controls the positive feedback loop in the next stage is put into oscillation mode, and the change in the Q value of the tape sensor L1 is reflected in the oscillation output. It is constructed so that the first and second transistors Q1 and Q2 become conductive only when the large amplitude oscillation output in the state of contact with the magnetic tape is half-wave rectified by converting it into a change and amplifying the amount of change. However, a low level output is derived from the collector of the second transistor Q2.

Therefore, when the aluminum foil comes into contact with the tape sensor L1,
The Q value of the tape sensor L1 decreases, the oscillation output also attenuates, the first and second transistors Q1 and Q2 become non-conductive, and the output level becomes high level.

Therefore, in the conventional example described above, the arrival of the end of the tape is detected as an increase in the output voltage level.

However, such conventional circuits inevitably suffer from high manufacturing costs due to the complexity of the circuits due to the arrangement of amplifiers.

Therefore, in view of the above points, the present invention proposes a tape end detection circuit with simplified circuit connections.

The present invention will be described below with reference to an embodiment shown in FIG.

In this embodiment, as shown in FIG. 2, the resonant coil of the Colpitts type oscillation circuit A is configured with a tape sensor L, and the base potential of the oscillation transistor Q3 is controlled by the first variable resistor VR1.
is adjusted so that the change in the oscillation output is maximized with respect to the change in the Q value of the tape sensor L, and the oscillation output is taken out at low impedance as the emitter output of the oscillation transistor through the half-wave rectifier path B. Fourth transistor Q4
to the base of the fourth transistor Q4 to generate an emitter current in the fourth transistor Q4, and apply the slider output of the second variable resistor VR2 constituting the emitter resistance to the fifth transistor Q5;
The second variable resistor R2 is adjusted so that the fifth transistor Q5 becomes conductive only when the magnetic tape is in contact with the magnetic tape.

Therefore, like the conventional circuit, the circuit of this embodiment detects the end of the tape and derives a high-level output, but its circuit structure is simpler than that of the conventional circuit, and it is possible to reduce manufacturing man-hours and manufacturing costs.

Further, since the oscillation output of the oscillation circuit is extracted as the emitter output of the oscillation transistor through a resistive impedance, there is no interference with other adjacent circuits, and there is no adverse effect.

Furthermore, matching with the next-stage rectifier circuit can be performed easily and without loss, which is highly effective.

[Brief explanation of the drawing]

FIG. 1 shows an example of a conventional circuit, and FIG. 2 shows an example of a circuit according to the present invention. Explanation of main drawing numbers, A...Colpittz type oscillation circuit, B...half wave rectifier circuit, L, L'!・・・・・・
...Tape sensor.

Claims (1)

[Scope of utility model registration request] In a certain magnetic recording and reproducing device, a tape sensor is provided that detects the contact of conductive foil placed at the beginning and end of a magnetic tape as a decrease in the Q value of an inductance element, and is connected to an oscillation transistor and the oscillation transistor. an oscillation circuit comprising a tuned circuit whose oscillation output is partially fed back to the input of the oscillation transistor; a rectifier circuit which extracts and rectifies the oscillation output as an emitter output of the oscillation transistor; 1. A tape end detection circuit comprising a switching circuit that is turned on and off according to the level of an output of a rectifier circuit, and controlling tape running based on the output of the switching circuit.