Abstract: An automatic vehicle headlamp intensity adjustement circuit includes a high sensor. A tuned rectifier circuit for producing a d.c. signal of magnitude dependent on the amplitude of the 50Hz (or other local supply frequency) component of the signal picked up by the sensor. A lamp current modulating circuit is controlled by this d.c. signal through the intermediary of an averaging circuit. The averaging circuit has a relatively long time constant and a timer is connected to reduce this time constant if the d.c. signal continues to fall for more than a predetermined period of time.

Abstract: A drive circuit for a piezo-electric crystal stack comprises an inductor, a first circuit including a diode and a transistor through which the inductor can be connected to a pair of d.c. supply terminals, the first circuit including a switch operable to reduce the current flow through the inductor, a second curcuit including a diode through which energy from the inductor is transferred to the stack of crystals when the current flow through the inductor is reduced. The drive circuit also includes means for transferring energy from the stack of crystals to the inductor when it is required to increase current flow in the inductor.

Abstract: A spark ignition system for a vehicle produces pulses representing the engine crankshaft angle. These pulses are counted, and compared with a datum signal which varies in accordance with engine conditions. When the two signals compared are equalled, then a spark is produced.

Abstract: A data transmission system for a road vehicle has an aerial on the road vehicle for picking up signals from an external transmitter. This aerial passes a signal to a receiver on the vehicle which in turn passes the information to a memory unit which stores the information at a fast rate and then supplies the information at a slow rate to an electrical voice synthesizer.

Abstract: A full wave rectifier comprises positive and negative supply lines, and a differential input amplifier which is powered by the positive and negative supply lines and which has its inverting input terminal connected through an impedance to an input terminal to which the a.c. signal to be rectified is fed. The non-inverting input terminal of the differential input amplifier is connected to a terminal at a potential intermediate the positive and negative supply lines, and a transistor has its base connected to the output terminal of the differential input amplifier. The emitter and collector of the transistor are connected through resistors to the supply lines, while the emitter of the transistor is also connected through an impedance to the inverting input terminal of the differential input amplifier, the output of the full wave rectifier being taken from the collector of the transistor.

Abstract: A direction indicator system for road vehicles, comprises an electrical circuit which is in the form of a single integrated circuit and which includes circuitry means externally connectible in at least two alternative ways to enable the indicator system to operate in any one of at least two different modes.

Abstract: A fault indicating system in a vehicle includes a d.c. source, a plurality of electrically operated devices operated by the d.c. source and a plurality of fault indicating units, one for each device. Each fault indicating unit is operable by a predetermined address signal, and on being operated produces after a delay an output representative of the operation condition of its device, each fault indicating unit having a different delay. A monitoring unit produces the predetermined address signal and receives the output signals from the fault indicating units. The monitoring unit operates in cycles, in each of which it has a transmission period in which it feeds the address signal to all the fault indicating units, and a plurality of receiving periods during which it receives the output signals from the fault indicating units in turn, warning means being operable by the monitoring unit to indicate a fault in any of the devices.