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 noise generator uses the thermal noise of a common diode junction. The circuit is from an...
This circuit can monitor the charge and discharge of batteries. The circuit is from a Linear...
This simple electroscope with bipolar transistors is not the most sensitive, but can detect static...