One application of the CD4051B is to use it in conjunction with a microcontroller to poll a keypad. Figure 9-1 shows the basic schematic for such a polling system. The microcontroller uses the channel select pins to cycle through the different channels while reading the input to see if a user is pressing any of the keys. This application is a very robust setup, allowing for multiple simultaneous key-presses with very little power consumption. This setup also uses very few pins on the microcontroller. The down side of polling is that the microcontroller must continually scan the keys for a press and can do little else during this process.

Figure 9-1 The CD4051B Being Used to Help Read Button Presses on a Keypad