Parallel-connected dialing signal transmission-inhibiting device for data transfer over a telephone link

A parallel-connected dialing signal detection and transmission-inhibiting device is disclosed which detects dual-tone multi-frequency dialing signals across tip and ring conductors of a telephone link and switches in an a.c. load that attenuates the dialing signals by at least 30 dB. This prevents action in response to the DTMF signals by a central office servicing the telephone link, thereby allowing commands-data to be transmitted within the home telephone wiring. Such commands can be used to invoke a speed/auto dialing function, to provide an intercom, to control appliances, etc. To allow fast response, the controller charges a capacitor of the a.c. load by connecting it across the tip and ring conductors in response to an off-hook condition. Then it is disconnected to allow a dial tone to reach a user at the telephone. Further transparency is provided by the fact that a single interfacing capacitor connects both the dialing signal detector and a tone generator to the tip line. This reduces the loading on the tip line by the device during periods when users are conversing on the telephone link.