VFD Clock

Posted on Feb 6, 2014

A vacuum fluorescent display (VFD) tube is a type of tube which consists of a hot cathode (filaments), anodes (phosphor) under a high vacuum condition in a glass envelope. This clock uses tube types 8843 or 8894 made by Sylvania in the early seventies. The cathode is made up of fine tungsten wires, coated by alkaline earth metal oxides, which emit

VFD Clock
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electrons when heated by an electric current. If electrons impinge on the phosphor-coated plates, they fluoresce, emitting light to indicate the 7-segments used in this tubes. Electrons can only reach (and "illuminate") a given plate element if the plate is at a positive potential with respect to the cathode. They have no grid compared to other VFD displays. Power Down Mode: tubes and supply can be totally switched off for a user programmed period in order to save energy and increase life expectancy of the tubes RTC drift compensation: Every RTC chip (RTC=Real Time Clock) does have a drift. This drift depends to the ambient temperature, buffer battery voltage, aging and other factors. This clock has a feature called drift compensation  which allows compensating that drift nearly to zero.

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