Circuit for detecting a paper at a desired position along a paper feed path with a one shot multivibrator actuating circuit

A print paper detecting circuit for detecting the presence of a print paper at a desired position along a paper feed path, said circuit comprising:

• an optical sensor disposed at the desired position and having a light emitting diode for emitting light and a phototransistor for receiving the light and producing an output signal corresponding to the received light;
• a current supply circuit, including a switch circuit, for supplying a high level of a driving current to said light emitting diode when said switch circuit is actuated,
• said current supply circuit comprising a transistor having its emitter-collector path connected in series with a resistor and said light-emitting diode across a voltage source, and a base;
• an actuating circuit, connected to said base of said transistor, for selectively actuating said switch circuit for a predetermined duration in response to a control signal;
• and
• an output circuit means for providing a paper detecting signal according to the output voltage from said phototransistor.

A print paper detecting circuit for detecting the presence of a print paper at a desired position along a paper feed path, said circuit comprising:

• an optical sensor disposed at the desired position and having a light emitting diode for emitting light and a phototransistor for receiving the light and producing an output signal corresponding to the received light;
• a current supply circuit, including a switch circuit, for supplying a high level of a driving current to said light emitting diode when said switch circuit is actuated;
• an actuating circuit for selectively actuating said switch circuit for a predetermined duration in response to a control signal;
• and
• an output circuit means for providing a paper detecting signal according to the output voltage from said phototransistor, and wherein said output circuit means comprises:
• an invertor, having a predetermined threshold value, for inverting the output voltage from said phototransistor;
• and a set-reset flip-flop circuit having a set input connected to receive an output signal from said invertor, a reset input to receive said control pulse, and an output for providing a signal indicating the detection of a paper by said phototransistor.