Found in Maxim's documentation from the 90's, this circuit uses an integrated from the time providing a 12 V output from 10 to 12 V inputs.
This circuit has a low level at its output (pin 8) when the input signal has a frequency of 10...
Found in a 1993 Electronics Experimenter Handbook, this circuit uses a multimeter to measure...
The circuit is from an old American publication. We can mount it with the BC548 and TIP31. The...