| 摘要 |
PURPOSE:To prevent abnormal transmission and reception of an acoustic coupler which uses batteries as a power source, by detecting a voltage drop right before abnormal reception is caused by a battery voltage drop and by giving the indication to an operator while stopping an acoustic output. CONSTITUTION:Key input data obtained from a key input part 11 is held in a buffer incorporated in a control part 12, and the logical level signal of the data is converted into an acoustic frequency signal by an output part 13 to drive the speaker 15 of an acoustic coupler 16. At a battery part 14, on the other hand, a battery voltage E is stabilized by a Zener diode CR2 through a resistance R5 and supplied to each part through a line 27. A potential obtained at point A by a resistance R1 and a variable resistor VR1 and a reference potential obtained by a resistance R2 and a Zener diode CR1 are compared mutually by a comparator 22 and when the battery voltage drops and the potential at point A drops below that at a point B, the output of the comparator 22 sets an FF23 to turn on an LED24, thereby stopping the operation by the control part 12. |
