Transmission control unit

A transmission control unit, for controlling the transmission and reception of analog electronic data between an electronic device and a main telephone unit having an electronically detachable handset without any use of acoustic coupling, comprising:

• a first terminal for detachably connecting the transmission control unit electronically to the main telephone unit;
• a second terminal for detachably connecting the transmission control unit electronically to the handset when the handset is electronically detached from the main telephone unit;
• a third terminal for detachably connecting the transmission control unit electronically to the electronic device;
• and
• an electronic circuit interconnecting said first, second, and third terminals and having switching means for connecting the first terminal only to the third terminal when analog electronic data is to be transmitted from the electronic device to the main telephone unit, and connecting the first terminal only to the second terminal when analog electronic data is not to be transmitted from the electronic device to the main telephone unit, said switching means being electronically responsive to a switching signal received from the electronic device through said third terminal for connecting said first terminal to said third terminal when analog electronic data is to be transmitted from the electronic device to the main telephone unit,
• wherein the electronic device has a transmit button which is pushed to generate a transmit command in order to effect transmission of analog electronic data from the electronic device to the main telephone unit,
• wherein said switching means includes a relay coupled to a switch group which is normally in an OFF position connecting said first terminal to said second terminal and which is responsive to the transmit command for effecting transmission from the electronic device through said third terminal for switching to an ON position disconnecting said first terminal from said second terminal and connecting said first terminal only to said third terminal when analog electronic data is to be transmitted from the electronic device to the main telephone unit, and further,
• wherein said electronic circuit includes a current-adjusting power source coupled between said third terminal and said switching means for adjusting a suitable loop current of the electronic device provided to said third terminal, so that said transmission control unit can be connected to any type of electronic device without requiring a matching modification thereof.