Playback search control device for a tape recorder
This application is a continuation of application Ser. No. 336,993, filed Jan. 4, 1982, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to tape recorders, and more particularly to a playback search control device for a tape recorder. 
     In a conventional playback search control device, when it is detected that a predetermined length of blank magnetic tape occurs after a signal such as music has been recorded, the tape recorder is set in a play mode, thus completing the playback search. Therefore, if while scanning in the forward direction a very long blank portion is encountered, the recorder will be set in a play mode but a long period of time may elapse from the time instant the tape recorder is set in a play mode until a recorded signal (e.g. music) is reproduced. If no recorded portion follows the blank portion having the predetermined length, the tape recorder is forced to continue to perform a useless play mode operation. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide a playback search control device in which the top (i.e. the beginning, or leading edge) of a recorded portion of a magnetic tape is positively detected, to thereby eliminate the wasting of timing. 
     In a playback search control device according to this invention, a counter is employed in such a manner that a clock pulse is applied to the clock input terminal of the counter and an audio pulse, which is obtained by converting the output audio signal of a reproducing head, is applied to the clear input terminal of the counter. The blank portion is detected from the fact that the count value of the counter has reached a predetermined value. Then, the audio pulse is applied to the clock input terminal, and the top, or leading edge, of a recorded portion of the tape is detected from the fact that the count value has reached another predetermined value. The machine then scans in reverse until the blank portion is again detected, at which time it switches to play mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of this invention will be described with reference to the accompanying drawings, in which: 
     FIG. 1 is a circuit diagram showing a playback top search control device according to the invention. 
     FIGS. 2(a) through 2(k) are time charts indicating the waveforms of signals at various locations in the circuit of FIG. 1; and 
     FIG. 2(l) is a diagram showing the variations in operation mode of a tape recorder. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, a recorded audio signal is picked up by a reproducing head 1 and is supplied through an equalizer amplifier 2 to amplifiers 3 and 4. The audio signal amplified by the amplifier 3 is reproduced by a loudspeaker SP. On the other hand, the audio signal amplified by the amplifier 4 is shaped by a Schmitt trigger circuit 5 into a pulsive audio signal, i.e., an audio pulse signal. That is, the amplifier 4 and the Schmitt trigger circuit 5 form a waveform conversion circuit. The output audio pulse of the Schmitt trigger circuit 5 is applied to first input terminals of NAND gates G 1  and G 3 . A clock pulse generator 6 outputs a clock pulse having a predetermined frequency, which is applied to a first input terminal of a NAND gate G 2 . 
     A search start control circuit 7 provides an &#34;L&#34; level signal at its output terminal before a playback search instruction signal is applied thereto, but the circuit 7 provides an &#34;H&#34; level signal when the search instruction signal is applied. The &#34;H&#34; level signal is applied to a cue instruction terminal (CUE) of a tape recorder mechanism control section 8, so that the tape recorder starts a cue operation (which is a FF operation with the reproducing head being in contact with the tape). In this case, a flip-flop circuit FF 1  is in a reset state, thus applying an &#34;H&#34; level signal through its Q terminal to second input terminals of the NAND gates G 1  and G 2 . Therefore, the clock pulse is supplied through the NAND gate G 2  and a NAND gate G 5  to a clock input terminal of a counter 9, and the audio pulse from the Schmitt trigger circuit 5 is supplied through the NAND gate G 1  and a NAND gate G 4  to a clear input terminal of the counter 9. 
     Therefore, when the tape recorder has started the cue operation in response to the playback search instruction signal applied to the start control circuit 7 and the reproducing head is in contact with a signal recorded portion of the tape, audio pulses are successively applied to the clear input terminal of the counter 9 and therefore the count value of the counter 9 is not increased. However, when the reproducing head comes to a blank portion between recorded portions of the tape then no audio pulses are supplied, and accordingly the count value of the counter 9 is increased. When the count value of the counter 9 reaches a first predetermined value K=2 N-1  (N being a natural number), the counter 9 outputs an &#34;H&#34; level signal through its output terminal Q N . The &#34;H&#34; level signal is applied to one input terminal of an AND gate G 7 . At the same time, an &#34;H&#34; level signal is applied to the other input terminal of the AND gate G 7  from the cue output terminal of the mechanism control section 8. Therefore, an &#34;H&#34;  level signal is applied to a CK terminal of the D-type flip-flop circuit FF 1 , to set the latter FF 1 . Therefore, the Q terminal of the D flip-flop circuit FF 1  is set to an &#34;L&#34; level, while the Q terminal is raised to an &#34;H&#34; level. Thus, when the reproducing head comes to the blank portion, as detected by the count N, the circuitry as reconfigured such that only the audio pules of the Schmitt trigger circuit 5 can thereafter be applied to the clock input terminal of the counter 9. There will, of course, be no audio pulses from the trigger circuit 5 during the blank portion of the tape, but the reconfiguration of the circuitry of FIG. 1 will now mean that the counter 9 will begin counting the audio pulses upon reaching a recorded portion of the tape. The counter 9 is designed as an N-bit counter, and therefore the counter 9 overflows and starts from zero again when counting the audio pulses. When the count value of the counter reaches a second predetermined value L=2 M-1  (M being a natural number, and M&lt;N), the counter 9 provides an &#34;H&#34; level signal at its output terminal Q M . This &#34;H&#34; level signal is a blank portion detection signal representative of the fact that the reproducing head has passed the end of a blank portion of the tape and is now detecting a recorded portion. 
     The D-type flip-flop FF 1  is in a set state as described above. Therefore, &#34;H&#34; level signals are applied to both input terminals of an AND gate G 6 , which outputs an &#34;H&#34; level signal. (It will be appreciated that, since M&lt;N, the Q M  output also occurs during counting of both audio and clock pulses. However, since FF 1  is reset in such a case, the Q M  output will not pass through gate G 6 .) This &#34;H&#34; level signal is applied to another D-type flip-flop circuit FF 2  to set the latter FF 2 , and is further applied through a gate G 10  and the gate G 4  to the counter 9 to clear the counter 9. When the D-type flip-flop circuit FF 2  is set, it applies an &#34;H&#34; level signal through its Q terminal to a review instruction terminal (RVW) of the mechanism control section 8. As a result, the tape recorder starts a review operation (which is a rewinding operation with the reproducing head kept in contact with the tape). In this case, the RVW output of the control circuit 8 resets FF 2  and the CUE output terminal of the mechanism control section 8 is set to the &#34;L&#34; level. Therefore, an &#34;H&#34; level signal from a gate G 8  is supplied to a clear terminal of the D-type flip-flop circuit FF 1  to reset the latter FF 1 . Thus, both the clock pulse and the audio pulse are now applied to the clock input terminal and the clear terminal of the counter 9, respectively. When, under this condition, the reproducing head comes back to the blank portion of the tape, the count value of the counter 9 begins to increase. When the count value reaches the N, the output terminal Q N  is raised to the &#34;H&#34; level. In this case, the Q terminal of the D-type flip-flop circuit FF 2  is at the &#34;H&#34; level, and the output of the gate G 8  is also at the &#34;H&#34; level. Therefore, a gate G 9  applies an &#34;H&#34; level signal to a play instruction input terminal (PLAY) of the mechanism control section 8, as a result of which the tape recorder is set in the play mode. Thus, the playback search operation has been completed. 
     The signal waveforms of various elements in the circuit of FIG. 1 are as shown in FIGS. 2(a) through 2(k). FIG. 2(a) shows the audio pulse from the Schmitt trigger circuit 5; FIG. 2(b), the clock pulse outputted by the clock pulse generator 6; FIG. 2(c), the input pulse to the clock input terminal of the counter 9; and FIG. 2(d), the input pulse to the clear terminal of the counter 9. FIGS. 2(e) and 2(f) show the output signals at the output terminals Q M  and Q N  of the counter 9, respectively; FIG. 2(g), the output signal from the cue output terminal of the mechanism control section 8; FIGS. 2(h) and 2(i), the output levels at the Q terminals of the flip-flops FF 1  and FF 2  ; and FIGS. 2(j) and 2(k), the signal waveforms of the review output and the play output of the mechanism control section 8. FIG. 2(l) shows the tape recorder operation mode variations with the signal waveform variations shown in FIGS. 2(a) through 2(k). 
     In the above-described embodiment, the counter 9 is set as an N-bit counter, and the terminal Q N  is employed as an overflow terminal; however, a count value which is obtained before overflowing takes place may instead by employed. In the latter case, a circuit to clear the counter 9 with the output at the terminal Q N  should be provided. 
     As is apparent from the above description, in the playback search control device according to the invention, the blank portion detection timing is set by allowing the counter to count a predetermined number of clock pulses, and the recorded portion detection timing is set by counting a predetermined number of pulses which are obtained from the output audio signal of the reproducing head. Therefore, two different kinds of timing can be set accurately by a signal counter. Thus, the playback search control device of the invention is relatively simple in circuitry.