Abstract: A circuit for protecting an electronic device from excessive voltages applied to an input or output terminal includes a solid state relay coupling the electronic device to the terminal. The solid state relay may include an opto-transistor coupled between the electronic device and the terminal and a light-emitting diode optically coupled to the opto-transistor. The solid state relay is coupled in series with a current limiting device, such as one or more enhancement mode field effect transistors, and an electromechanical relay. A voltage detector coupled to the terminal detects a voltage larger than a specific value and causes current to flow thorough the light-emitting diode, thereby interrupting the coupling between the terminal and the electronic device. The voltage detector may be coupled between two spaced-apart connections to the coupling path between the terminal to the electronic device so that the voltage detector avoids diverting current from the coupling path.

Abstract: A circuit for protecting an electronic device from excessive voltages applied to an input or output terminal includes a solid state relay coupling the electronic device to the terminal. The solid state relay may include an opto-transistor coupled between the electronic device and the terminal and a light emitting diode optically coupled to the opto-transistor. The solid state relay is coupled in series with a current limiting device, such as one or more enhancement mode field effect transistors. A voltage detector coupled to the terminal detects a voltage larger than a specific value and causes current to flow thorough the light emitting diode, thereby interrupting the coupling between the terminal and the electronic device. The voltage detector may be coupled between two spaced-apart connections to the coupling path between the terminal to the electronic device so that the voltage detector avoids diverting current from the coupling path.

Abstract: A tennis teaching machine has a ball hopper slidably mounted on a vertical support. A hollow extension arm protrudes from the ball hopper and has a ball projection mechanism at the end. A rotating ball tray supported within the ball hopper supplies balls to the extension arm and ball projection mechanism. A control unit has a tapedeck which automatically activates the ball projection mechanism when a sensor detects a strip of metal foil on magnetic tape played by a tapedeck. The tennis teaching machine is positioned between two training mats upon which various tennis technique training indicia are inscribed. The student listens to instructions from the control unit and strokes a tennis ball dropped on cue from the extension arm. When stroking the tennis ball, the student positions his feet and racket as indicated by the training indicia on the mats.

Abstract: A coin operated music machine which permits persons purchasing musical selections on the machine the opportunity of making additional selections over and above the amount of records and playing time to which he would be entitled by the deposit of coins into the machine. After the initial coin has been deposited into the machine, the player is offered the opportunity to make an additional coin deposit for which he may receive additional plays in addition to those purchased by the two coins. The right to receive the "Bonus Play" will be indicated on the machine but the player need not exercise the right to such play and can reject it by merely selecting the recordings which have been purchased by the deposit of the first coin. If the player decides to utilize the "Bonus Play" he will always receive the normal number of selections for the second coin but may additionally receive extra plays above the normal number of selections for a coin.