This amplifier for electrometer can work with currents of 0.1 pA in a band of 1 Hz. The circuit is from NASA in a publication of the 60s. Transistors are general purpose types.
This circuit was found in a 1965 General Electric manual. What it does is give a warning if you...
The sensor in this circuit is a BA315 diode. Other diodes can be experimented, but this is one...
This circuit turns on your car's backlight when a vehicle coming from behind gets too close to it...