| 摘要 |
PURPOSE:To reduce number of components by allowing a frequency analyzer to extract a desired signal, taking a ratio with other noise frequency component and deciding the stregth of an electric fied so as to attain the use of a microcomputer. CONSTITUTION:The frequency analyzer 13 decomposes an input signal into 16 kinds of frequencies (f0-f15), a comparator 14 compares the frequency component, a component of the maximum amplitude is produced to an output (a) and the remaining components are produced to an output (b), which is fed to an adder 15. That is, when an input signal shown in Fig. (b) exists, an f9 is produced at the output (a), the remaining frequencies are produced to the output (b), they are added by the adder circuit 15, and an amplitude A is outputted. A deciding circuit 16 compares and discriminates the amplitude of the signal f9 and the output A and the ratio of the amplitudes controls an LED drive circuit 9. Thus, when the strength of electric field is very strong, the ratio of the signal f9 and A is large, LEDs of the circuit 9 are all lighted, and when the electric field strength is weak, the number of lighted LEDs is decreased. On the other hand, the signal f9 is fed to an information decoding circuit via a gate circuit 17 only when a signal from the deciding circuit 6 exists.
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