APPARATUS FOR CONTACTLESS TRANSMISSION OF DTMF SIGNALS

摘要

In the device there is a standard portable keyboard (1) of the voice frequency dialling used with built-in dynamic speaker (2), wherein in the receiving circuit of the voice frequency dialling there is a decoder (7) of the signal of the voice frequency dialling connected with the condenser (6) and resistance (8) at the input of the receiving circuit. At the input of the receiving circuit of the voice frequency dialling there is an infra transistor (5) connected, the cathode of which is connected with the common ground (4) of the voice frequency dialling circuit and the anode is connected with the input of the receiving circuit and the resistance (10), the other end of which is connected with the driving voltage (9), whilst the standard portable keyboard (1) is modified by serial connection of the transmitting infra led diode (3) into the circuit of the built-in dynamic speaker (2).