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.
The integrated circuit used in this application is not very common. The circuit is intended for...
The focused circuit was found in the National Semiconductor's Linear Applications Handbook of...
The TDA2040 is not a common IC these days, but if you find one you can build this high quality...