Practical Electronics/IC/4066

The 4066 contains 4 analogue bilateral switches, each with an active-high enable input (A) and two input/outputs (X and Y). When the enable input is set high, the X and Y terminals are connected by a low impedance; this is the on condition. When the enable is low, there is a high impedance path between X and Y, and the switch is off.

The 4066 is pin-compatible with the 4016, but has a significantly lower on impedance and more constant on resistance over the full range of input voltage. Therefore, the 4066 is preferable to the 4016 in most cases.