Found in a 1980s American documentation, this circuit uses programmable unijunction transistors of the time. The time interval obtained depends on the capacitors that can be changed.
This circuit is from 1977 documentation, but can be assembled with BC548 for Q1, Q2 and Q4, BC558...
Found in American documentation from the 90s, this circuit uses components that are still common...
This high impedance input amplifier is suitable for the use with piezoelectric sources such as...