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 configuration is from a 1964 US documentation valid for any FET. The range of power voltages...
The operational amplifier used in this circuit from a 1970s publication is no longer easily found...
This circuit was found in an old American documentation. It can operate with signals from 40 Hz to...