Using JFETs, this circuit from a 90’s American documentation can generate signals of 0.15 Hz. The JFET can be of any general-purpose type like the BF245 or MPF102.
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...