Here is the demonstration of a stable multivibrator using 7404 inverter. Added with few transistors, this can blink three LEDs for the demonstration.
If supposing that the electric charge isn't stored up in Cy, the electric current flows with the inverter A output Cy Ry Dy inverter B output.
At first, the condition of the inverter B is unsettled but because the output of the inverter B is not totally in the high level condition, above-mentioned electric current flows.
When the electric charge begins to store up in Cy, Cy can be seen like the short circuit condition. So, the input of the inverter B becomes the high level condition. The output of the inverter B becomes the low level and above-mentioned electric current route is fully formed.
However, because it is a small amount, most of the electric currents flow in the route which passes Ry.
When the electric charge is stored up in Cy, the electric current decreases. Input voltage of the inverter B goes down with it and approaches the threshold voltage of the inverter B. Because the output of the inverter B is the low level (being 0V almost), the electric current alwayses fall through more through Ry, Dy and the input voltage of the inverter B becomes the threshold voltage (VT).
http://www.hobby-elec.org/e_ckt6.htm
