This 2005 Linear Technology circuit has separate outputs for monitoring the charge and discharge of a battery. Formulas next to the diagram let you calculate the components.
This is the typical circuit of an FET amplifier stage in the common source configuration. The circuit is...
Pressing and releasing S, the capacitor C1 charges and discharge slowly through the oscillator...
For the 7 to 10 MHz band L1 is formed by 3 turns of 22 to 28 AWG wire in a ferrite core 15 to 20...