Abstract: Circuitry for use in a voltage measurement and display device provides automatic function change for measurement of AC or DC voltages. Voltage measurement in a predetermined mode (DC, for example), is assumed. Upon detection of an input voltage component exceeding a predetermined threshold of the other mode, (AC, for example), the measurement function is changed to that other mode. Upon detection of a component in the other mode, in a range between the predetermined threshold and a second (preferably lower) threshold, an annunciator is activated to alert the user to the presence of the other mode (AC) voltage, for manual activation of a function-selecting switch if desired. Thus, in a specific embodiment, automatic function changeover is provided upon detection of AC components exceeding a predetermined threshold, along with activation of an AC annunciator.

Abstract: A hysteresis type battery charger includes a circuit for monitoring battery voltage and in response controlling a pass transistor to supply charging current to a battery. When the battery voltage is below a first predetermined value, high charging rate current is supplied to the battery; when the battery voltage is above a second predetermined value, the battery is supplied with trickle charging current. First and second light emitting diodes (LEDs) are selectively energized to indicate whether the battery is receiving high charging rate current or trickle charging current. The second LED is connected in circuit with the pass transistor to provide charging current foldback during excessive current demand, e.g., short circuit. The battery charger includes a low battery monitor that is energized when the expected battery lifetime is at a predetermined value, e.g., one hour.

Abstract: In a device for mounting a liquid crystal display (LCD) to a circuit board, a holder is positioned between the LCD and the circuit board and a cover member positioned around the LCD and holder is secured to the board. The LCD is recessed slightly within the cover member and is exposed through the cover at a display opening. To compensate for the recess of the LCD within the cover member, an optically clear lens is positioned with its lower surface in contact with the LCD and upper surface extending outwardly through the display opening. An image of the alphanumeric characters displayed by the LCD is projected on the outer surface of the lens of create an optical illusion of the display characters at the surface of the cover.

Abstract: A digital multimeter having a tone generating circuitry and operable in a tone mode of operation for providing an audible indication when a measured electrical characteristic has a predetermined relationship with a reference value. The audible indication may be provided when a voltage level exceeds a preselectable limit, such as 1 or 2 volts. Predetermined limits for resistance values may also be selected for actuation of the audible tone. The device may be utilized as a conventional multimeter when the tone mode is non-operative.

Abstract: An offset circuit for use in providing an offset signal to an analog-to-digital converter. The analog-to-digital converter has an integrator for performing signal integrate operations and is connected to a digital display. The offset circuit is gated to provide a variable offset current directly to the integrator of the analog-to-digital converter, thereby eliminating adverse loading effects on the high input impedance of the analog-to-digital converter.

Abstract: A track and hold system for use with a test instrument such as a multimeter includes an input circuit, a buffer amplifier, a storage device such as a capacitor, an output amplifier, an output circuit, a detector for detecting a pulse on a signal passing from the input to the output, and a switch responsive to the detector for isolating the storage device from the input circuit but not the output circuit for a predetermined period. The system also includes a timer responsive to the detector to provide an isolation command to the switch for the predetermined period. Further, the system includes a delay circuit, responsive to the detector, for interposing a delay of variable duration prior to activating the timer.

Abstract: Digital display devices and digital timepieces in which the display is remotely updated. The method permits continuous updating with simple and inexpensive TTL Logic and less frequent updating with microprocessor means. The remote updating signal can be transmitted through telephone means, broadcast means or other standard communications means to simultaneously update multiple digital displays.A single improved digital display device can be utilized as a master for controlling the display of multiple devices.