We found this circuit in an old Mullard (Philips) documentation. The sensor consists of a reed-switch that is coupled to a magnet on one of the wheels of the vehicle.
We found this circuit in documentation from the 1950s. The circuit basically applies to germanium...
With the configuration shown in the figure, a common 12 V lamp lights up when light no longer...
The purpose of this circuit is to re-trigger slow scan circuits used in the 1980s on low frequency...