We found this circuit in a documentation from the 90's. The coil has its characteristics given next to the diagram. Power is provided by a 9 V battery and a range of a few tens of meters.
We found this simple circuit with headphones listening in Radio Electronics magazine from March...
This circuit was obtained from Maxim documentation. The circuit has 4.5 and 5.5V thresholds for...
This complementary-output amplifier can be used to source a good qualuty signal to high impedance...