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.
This configuration is from a 1964 US documentation valid for any FET. The range of power voltages...
The operational amplifier used in this circuit from a 1970s publication is no longer easily found...
This circuit was found in an old American documentation. It can operate with signals from 40 Hz to...