Abstract: An operational amplifier is disclosed having a phototransistor at its input for reading a bar code wherein the saturation point of an operational amplifier is controlled by a clamping feedback voltage having a positive control controlling the saturation point of the operational amplifier while prohibiting the operational amplifier from reaching its saturation point.

Abstract: A tactile feel device which provides a characteristic resistance to movement, and breakaway feel to signal the operator that movement and accompanying function, such as switching, has been accomplished. Resistance to movement is provided by spring biasing means for the initial stroke of the device, by spring biasing means plus magnetic force at the end of the initial stroke, and by spring biasing means only, after magnetic breakaway at the end of the initial stroke, to provide a characteristic breakaway feel. The device is shown and described in connection with a light pen which generates a signal when pressed against a cathode-ray-tube faceplate. The characteristic breakaway feel signals the operator that the tip or probe of the pen has been sufficiently pressed against the cathode-ray-tube to generate the appropriate signal in the light pen.