Simple Key code lock switch circuit using IC-4017 digital, uses 10 switch bottom to control output by Relay. No microcontroller so easier and cheaper!
It may be difficult. In the design of the BCD signal generator circuit by pressing a key. Here is how you make a keyboard encoder circuit for 16 keypads.
The simple bounceless switch circuit. It is one kind of electronic switches, high quality, and low noise. They are suitable for the digital circuits. Why?