Digital Electronics - Multivibrators and 555 Timer

When extremely critical timing is required, a quartz crystal can be used.

In the 74121, which is nonretriggerable, any triggers that come in before the end of the timing cycle are ignored.

A comparator simply outputs a HIGH or LOW based on a comparison of the voltage levels at its input.

The 74S124 TTL chip is a voltage-controlled oscillator that will generate a specific frequency at V_out.

A single Schmitt trigger inverter is all that is needed to build a simple astable multivibrator.