Autoranging digital luxmeter

摘要

An autoranging digital luxmeter is disclosed in which the current from a photocell is converted into a voltage by cascaded, variable gain amplifiers. The output of the amplifiers is coupled by a sample-and-hold circuit to an analogue-to-digital converter, the output of which is a digital representation of lux. The output of the amplifiers is also connected to limit comparison circuitry which, by way of an up- down counter, varies the gain of one or both of the amplifiers.