| 摘要 |
<p>PURPOSE:To prevent a built-in battery from being abnormally consumed by deciding the start and final ends of a magnetic tape based upon an output voltage corresponding to the rotational frequency of feeding and winding reels and lighting up a light emitting element. CONSTITUTION:When the rotational frequency of the feeding reel is increased in the vicinity of the final end of a video tape and a reel pulse SP2 with a high frequency band is outputted, the pulse SP2 is shaped at its waveform, the shaped signal is applied to a frequency conversion circuit 14 and a DC voltage corresponding to the frequency is outputted to the non-inversional input terminal of a comparator 16. When the DC voltage exceeds 3V, 5V voltage is outputted from the comparator 16 and impressed to the base of an output transistor(TR) Q4 through a diode D4. Thereby, the TR Q4 is turned on and a power supply voltage is impressed to an LED D1 to turn on the LED D1. Since the LED D1 is turned on only when the tape exists in the vicinity of the start or end terminal of the tape, power consumption is sharply reduced and the consumption of the built-in battery is suppressed.</p> |
