Using this scheme can be built a very simple electronic channel selector, using very few electronic components. The channel selector allow selection of four positions and is built using integrated circuit 74hct154 some classic electronic parts.
Switches are connecting to the decoder inputs by a resistance, an LED and a transistor. Transistor is in parallel with the switch, so that clicking has no effect unless the transistor is blocked
Four transistors are controlled by each decoder output resistance of 1 k.
When power is connected, none of the transistors does not conduct (IC1's input state is 1111 and pin 17 of decoder logic is in state H).
If you press one of the switches corresponding input bit in IC1 goes to logic state L (this change of input code and output corresponding to the pressed switch goes to logic state H).