The CD 4001 is a very versatile CMOS chip.
Follow the inputs and note when the LED is illuminated.
Gating
Do not leave an input "open" (non-connected) as the high input impedance (approx 10M)
will pick up noise and create faulty operation.
The secret to understanding the operation of
the gate is show in the diagram on the right.
It is called Gating.
When one input is held Low, the signal on the other input
will be inverted by the gate and appear on the output.
When one input is held High, the output is a constant Low.
This is also shown
in the 1kHz tone circuit below.
