This circuit is from an old Mullard (Philips) manual with applications using the 555. Choosing appropriately the resistors and the timing capacitors, the ranges obtained can exceed days.
We found this sensitive moisture detector in an old documentation. The circuit uses a common JFET,...
This circuit, with the assembly in a contact matrix, was found in a publication from the 90s. The...
This modulator circuit for transmitters was found in American documentation from 1964. It can be...