This circuit was found in a 1970s General Electric documentation. This circuit already used an emitting LED. The circuit operates at frequencies from 50 Hz to 50 kHz with short pulses
This application is not modern since few computers have parallel ports. But you can use this...
Using a 741 op-amp this circuit high-pass to 10 kHz was found in the February 1995 issue of...
Found in a 1969 EEE, this circuit is based on an operational amplifier of the time and on old type...