| 摘要 |
<p>The arrangement is used with a two-way telephone set powered via the subscriber line. The aim is to redesign the hold circuit in a simple, low-cost fashion to function as the dial pulse contact, where DC isolation of the line and speech circuit must be guaranteed, providing an arrangement which can be integrated and switched using the keys of a standard keypad. This is achieved in that the current path provided with a load resistor in the hold circuit to terminate the subscriber line is connected through and opened between the wires of the subscriber line in time with the dial pulses, while the load resistor is by-passed. The by-pass is effected by means of transistors, which are controlled by the microprocessor via a transistor-optocoupler. The circuit arrangement is used in two-way telephone sets. <IMAGE></p> |
