Abstract: An automatic telephone answering machine of the kind employing a microcomputer for switching from one mode of operation to another is arranged to switch from the "stop" mode to the "automatic answer" mode in response to recurring ring signals transmitted during an incoming phone call, provided those signals meet criteria such as duration of ring, length of interval between successive rings, and a minimum period of recurring ring signals. The mode switching arrangement causes the machine to switch to the "automatic answer" mode and then answer the call during the same phone call to enable the caller to confirm by receipt of the machine's outgoing announcement that the mode switch has occurred.

Abstract: Detector circuitry monitors the line voltage on a telephone line to detect an off-hook condition. In order to accomodate varying line voltages and noise conditions, the circuitry automatically selects a threshold off-hook voltage by an iterative initialization procedure which is initiated on circuit power-up. The intialization procedure repeatedly compares the threshold voltage to the actual line voltage over a period of time to eliminate false off-hook detection due to noise.

Abstract: An indexing device for providing signals identifying the address in a memory device of stored information corresponding to any selected listing in the index has a housing in which is stacked a quantity of index cards of the type enabling a plurality of listings to be entered on each card. The housing can be closed by a hinged cover which carries an indicator that can be moved to line up with card identifying indicia marked on the cover. The indicator is pivotally mounted on a carriage that is slidably mounted at one edge of the cover. Disposed in the housing along the path of travel of the slidable indicator is a position sensor which detects the position of the indicator at stations which are disposed along the indicator's travel path to match the alignment of the indicator with the card identifying indicia on the cover.