Abstract: A line circuit is described which provides isolated power to a subscriber telephone line in a manner that produces a constant power characteristic over the normal range of telephone line loop resistance. The isolated feed characteristic of the present invention simplifies protection against lightning and other transients. The constant power characteristic limits power dissipation under short loop, i.e. low resistance, or short circuit conditions yet allows enough current flow under short loop conditions to activate the voice level reducing varistor in the telephone sufficiently to prevent excessive loudness. This eliminates the need for additional circuits at the telephone central office for detecting short loops and for providing voice frequency (VF) level attenuation under such conditions.

Abstract: A pulse discriminator circuit for use in a closed loop scanning and positioning system for finding and positioning white blood cells. The surface of a slide is scanned to produce an optical signal which is converted by a sensor into an electrical signal. This signal is applied to the pulse discriminator circuit which provides an output pulse only when a white blood cell is being scanned. The output of the pulse discriminator is coupled to a logic circuit which produces signals that are used to drive the microscope stage to cause the white blood cell to be positioned within a small aperture in the optical system.

Abstract: In a system which automatically analyzes laboratory slides, the adjustable objective lens is automatically focused. A beam splitter splits light from the slide into two parts. One slide image is projected to an actual image plane where it is converted into electrical signals representing the optical characteristics of the slide. The other slide image is projected to a parfocal image plane at which two light sensing devices for the focusing system are positioned. One light sensing device is in front of the parfocal image plane and the other is behind the parfocal image plane. These light sensing devices produce electrical signals representing the position of the actual image plane with respect to the desired image plane. The electric signals are differentiated and then applied to a comparator which supplies pulses to a stepping motor which moves the objective lens.