Remote control

DETAILED DESCRIPTION According to one aspect of the present invention, there is provided a slave receiver for detecting commands in the form of digital signals modulated on a cyclic carrier, the receiver comprising means responsive to the carrier to determine the digital values of the digital signals in dependence upon the number of cycles of carriers within time windows defined by the receiver, characterised in that the responsive means comprises an input circuit having an output stage switchable between two states to and produce a binary signal and capacitive means having charging and discharging circuit means so responsive to said carrier that: (a) the output stage has a first state when said carrier is absent; (b) when the carrier has been present above a given frequency and for a first given time sufficient charge accumulates on the capacitive means to change the output stage to its second state; (c) a subsequent break in the carrier of a length greater than a second given time (substantially less than the first time) causes a change of charge on the capacitive means to change the output stage to its first state; (d) when said carrier is subsequently restored, then the output will remain in the first state for a time directly related to the length of said break before sufficient charge again accumulates to change the state to said second state; and (e) a cyclic signal of a frequency substantially below the given frequency cannot cause sufficient charge to accumulate to cause said output stage to attain its second state, the receiver further comprising means for processing the binary signal within said time windows to determine the binary values therefrom, It will be seen that a digital counter as used in UK Specification No.
1592971 can be avoided by the use of capacitive means to accumulate charge dependent upon the number and frequency of carrier cycles.
More specifically, the resulting binary signal is suitable for processing by a microprocessor, e.
g.
by measuring the time for which the binary signal is in its second state in a window to determine the digital values, yet still discriminate against noise