Abstract: A receiver amplifier for amplifying a photoelectric current produced by a light-sensitive semiconductor component. The amplifier includes an amplifier transistor, a capacitor connected between the light-sensitive conductor component and the amplifier transistor for isolating signals with a frequency below a certain threshold delivered by the semiconductor components from the amplifier transistor, and a second transistor connected to the amplifier transistor for producing a current which compensates for changes in the current produced by the light-sensitive semiconductor component in response to light pulses.

Abstract: A remote-control lock system has a transmitter that can be set to emit any one of a succession of differently coded signals, a receiver that can be set to respond to any one of the succession of signals, and a lock operable by the receiver when it receives the signal it is set to. Initially the transmitter is set to emit a predetermined one of the succession of signals and the receiver is set to respond to the predetermined one of the signals. Thereafter, after each emission by the transmitter and reception by the receiver, the transmitter and receiver are reset to the next of the signals in the succession except after the last signal of the succession has been emitted and received in which case the transmitter and receiver are reset to the first of the succession of signals. Thus each actuation of the transmitter change the code that will open the lock.