By "switchboard", do you mean "keyboard". You mentioned "E", implying you want several letters other than "E". Keyboards are amazingly complicated and you'll have a miserable time if you try to design a PCB for one. Possibly, you mean something like a 12 key or 16 key keypad. These are also difficult to make at home and amazingly cheap, so better to buy. If you just mean a few switches, then you just need the switch and at least a resistor and maybe a capacitor. One end of each switch is usually wired to 0V and the other to the resistor and to a pin on the Arduino or whatever. The other end of the resistor is usually wired to +5V, or maybe +3.3V for some modern ICs.
Good luck.