Circuit for applying alpha/numeric data to a TV receiver

摘要

An electrical circuit for allowing the use of a TV receiver to display alpha/numeric data includes a pair of monostable multivibrators, logic circuitry and a tri-state gate for shaping and mixing digital horizontal and vertical retrace sync signals and alpha/numeric video signals to create a properly proportioned composite thereof. The circuit further includes an oscillator for generating a RF carrier signal, a field-effect transistor (FET) coupled between the oscillator and the output of the circuit which is adapted to be coupled to the antenna terminal of the TV receiver, and an emitter-follower device which feeds the composite signal to the FET for producing amplitude modulation of the RF carrier signal by the FET and transmission of the modulated signal to the TV receiver antenna terminals.