JPS5916335B2 - Tape end detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting a tape end, particularly a predetermined number N minutes before the tape end, when the tape is running in a tape recorder.

In conventional tape recorders, devices are known that detect the end of the tape during tape running and automatically stop the tape running. Knowing this is useful for practical purposes.

In other words, if you can prepare to change the tape before reaching the end, and if you can predict that changing the tape after reaching the end will result in interruption of music recording in the middle of the song, for example, It becomes possible to perform operations such as stopping recording at a good point in the song before reaching the end. The present invention provides a predetermined number of minutes before the end of the tape (N
The purpose of the present invention is to provide a device that electrically detects a point in time (an arbitrary number) with high precision and displays it.

Embodiments of the present invention will be described in detail below with reference to the drawings.

The sensor 1 of FIG. 1 generates an electrical intermittent signal proportional to the rotational speed of the tape reel. For example, as an example of an optical sensor, a disc with transparent parts and opaque parts arranged alternately is provided so as to be rotatable in conjunction with a tape reel, and a light emitting element and a photoconductive light receiving element are arranged facing each other with the disc in between. , the rotational speed of the tape reel can be detected electrically. The output pulse signal obtained by the sensor 1 has the waveform shown in FIG.
. decreases. This pulse signal is input to the one-shot multivibrator 2 and 3, and the one-shot multivibrator 2 produces the output pulse shown in FIG.
The switch SWI is turned on during the tl period of this output pulse. The output of the one-shot multivibrator 3 having the waveform shown in FIG. 2c is input to the one-shot multivibrator 4, and the output having the waveform shown in FIG. During this period, the switch SW2 is turned ON. All multivibrators operate at the falling edge of the input signal,
One shot multivibrator 3 is switch SWI
Switches SWI and SW2 are provided to temporally shift the ON operation periods of both switches so that they do not turn ON at the same time.Although switches SWI and SW2 are shown mechanically in FIG. 1, they are actually semiconductor devices. It consists of an electronic switch using, etc. If switches SWl and SW2 become 0N at the same time, the voltage at point B of the circuit in FIG. It is desirable to double the setting. The power supply includes a constant current circuit 5, a changeover switch SW3, and a capacitor C.
1, C2 or C3 are connected in series, and the switch SW2 is connected between the junction A of the constant current circuit 5 and the switch SW3 and the ground. Further, the voltage at point A is applied to the input of a voltage comparator circuit (Schmitt circuit) 6 via SWl. The input of the Schmitt circuit 6 is grounded via a capacitor CB. When the voltage at point B on the input side of the Schmitts circuit 6 drops below the operation start voltage of the Schmitts circuit, an indicator lamp or LED, etc. 7 connected to the output of the Schmitts circuit
is lit, thereby indicating that the tape is about to end, eg, several minutes ago. Output waveform of one-shot multipipulator 4 (
During period t1 from the rising edge of d) in Figure 2, switch SW2
is activated and the charge stored in the capacitor C1 is discharged, so that the voltage at point A becomes O level as shown in FIG. 2e. Thereafter, after a period T3 has elapsed, charging of the capacitor C is started from the time when the switch SW2 is turned off, and the charging voltage increases at a gradient θ as shown in FIG. 2e. Next, when the switch SWl is closed at the rising edge of the output waveform of the one-shot multipipulator 2 (Fig. 2a),
Waveform e (17) At point S, the voltage at point A is sampled to the Schmitt circuit input. Waveform f shows the voltage at point B. As the end of the tape approaches, the rotational speed of the supply reel increases so that the pulse interval T of the output pulses of sensor 1 increases.

gradually decreases. On the other hand, since the output pulse widths t1-T3 of each multivibrator 2-4 are predetermined values specific to each multivibrator, the output pulse interval T of the sensor 1.
When , the sampling period becomes shorter and the sampling pressure decreases. To explain this using the waveform diagrams in Figures 3 and 4, Figure 3 shows the case when the rotational speed of the supply reel is at a certain value, and Figure 4 shows the case when the rotational speed becomes slightly higher. It shows. The pulse interval of the sensor output pulses at this time is TO>tl.
Therefore, due to the output waveform d of the one-shot multipipe radar having a pulse width T3, the voltage at point A is equal to the voltage at point C of waveform e.
The voltage begins to rise from 0 and continues to rise at a gradient θ, and the voltage immediately before the rising point of the waveform e is sampled to the Schmitt circuit as the sampling voltage VBl. Similarly, in the case of FIG. 4, the voltage starts to rise from point D, continues to rise at the same slope θ, and is sampled at voltage B2. The sampling voltage difference to the Schmitt circuit 6 at this time is ΔVB=VBI-VB2. The present invention is characterized in that the pulse width T3 is increased and the slope θ is increased to increase the sampling voltage difference, thereby improving the accuracy of detection before a predetermined end of the tape.

That is, the pulse width of the output pulse waveform d of the one-shot multipipulator 4 is changed from T3 to t! If the voltage rise slope of the voltage waveform e at point A is increased from θ to θ5, the starting points of voltage rise will be point C and child point, respectively, as shown in Figures 3 and 4. . Therefore, the sampling voltage difference is △VB'=VBl-V
B3, △VB'>△VB is enlarged.

As is clear from FIGS. 2 and 3, the pulse width T3
is T3kuT. - It is possible to expand within the range of T2. Note that the pulse widths t1 and T2 are much smaller than T3. The switch SB3 in the above embodiment is
It is a mechanical changeover switch, and the slope is made variable in response to multiple types of tape thickness, so that the value of N, which is set N minutes before the end of the tape, does not change due to changes in tape thickness. This is a switch for changing the electric capacity in accordance with a predetermined tape thickness.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of an embodiment of the present invention, FIG. 2 is a diagram of each signal waveform in the circuit of the above embodiment, and FIGS. 3 and 4 show the above embodiment when the tape running speed is low and high, respectively. 3 is a diagram of each signal waveform in the circuit. FIG. Explanation of symbols, 1...Rotation speed center, 2, 3
, 4... One-shot multipipulator, 5
... Constant current circuit, 6 ... Schmitt circuit, 7 ... Display lamp.

Claims (1)

[Claims] 1. A tape reel rotation speed sensor that generates an electrical intermittent signal proportional to the rotation speed of the tape reel, and a first switch element that receives the output signal of the sensor and operates a first switch element that intermittents the input to the voltage comparison circuit. A one-shot multivibrator, a second one-shot multivibrator that inputs the output signal of the sensor and outputs it to a third one-shot multivibrator, and is connected in parallel to the input circuit of the voltage comparison circuit via the first switch element. a connected capacitor, and a capacitor connected in parallel with the capacitor,
A tape end detection circuit comprising: a second switch element operated by the output of the third one-shot multivibrator; and a display device connected to the output of the voltage comparison circuit.