| 摘要 |
PURPOSE:To decrease the number of transmission/reception lines, by adding a Zener diode to each station and transmitting signals among plural stations by means of a double-core twist cable. CONSTITUTION:Transistors TRT1 and TRT2 serving as elements for transmission are turned off while both stations A and B are not performing transmission. In such a case, a line 1' is cut off and transmits no current, and therefore light emitting diodes 21a and 22a in receiving photocouplers 21 and 22 emit to light. Thus phototransistors 21b and 22b corresponding to the diodes 21a and 22a are turned off. When the station A turns on the TRT1 with a transmitting signal (a), the line 1' conducts. Then a current flows in order of a current limiting resistance R1, the TRT1 the diode 21a in the coupler 21, the line 1', a current limiter R2 within the station B, a Zener diode 24 and the diode 22a in the coupler 22. When the current flows to the diode 22a at the station B, the diode 22a emits light to turn on the phototransistor 22b. |
