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.
This circuit works only with carbon microphones, due its low impedance. The speaker should be good or...
This circuit produces a sinusoidal signal whose frequency can be calculated using the formula next...
This circuit was found in the 1987 Radio Electronics magazine. The components used are integrated...