In the design of the BCD signal circuit that defined by pressing a key is difficult for a electronics beginner so much.
With this circuit so be the simple answer that can be used as versatile, because circuit is designed using a single IC follow the circuit shown in Figure 1. Key input circuit connected in the matrix format, with the signal from the Row and Column each of 4 rows, enable to get the code number 16 stage from 0-15. The binary code output to pin 14,15,16,17 respectively. When you press a key to the pulse signal output from the pin 12 with every time. The signal pulse is short time the one only. We call this that the Strobe signal for the control circuit used to be connected to output other circuit. The keys switch is used as a matrix. You may have to use self. By the positions of the switch. The new requirements, or if you want convenience may will be find a key block for the phone keys as well.
The number keys are used. May be a key to the 0-9 keys, leaving only blank AF, the voltage applied to the circuit, this is a 5V.
C1, C2_________________0.1 uF 63V
C3_____________________0.01 uF 50V
In the creation we put the electronic device in the PCB Perforated board as shown in Figure 2. For a key switch we did not design the PCB sheet. To help you make the switch to a design or pattern to suit your needs.