# Using a 4-1 multiplexer

I have a 4-1 multiplexer. I am trying to learn how to use it and I understand the logic well enough, but since I have never had any electronics training, my knowledge is somewhat limited and without actual circuit diagrams on any online resource, it is very confusing. what I am confused about is how do you send inputs to the MUX. Do we need to have a full circuit from positive to ground and then have a branch coming out of that circuit going into the MUX? If someone could explain a simple input like say (0 1 0 1) with selectors (1 1) with a circuit diagram (which shows the power supply), that would be great.

• The first place to start is the datasheet for the part you have. For one thing, we don't know if it is an analog or digital multiplexer. Some details will depend on the logic family and individual part details. Sep 18, 2020 at 14:41
• @SpehroPefhany I did start with the datasheet (‎SN74HC153N) but I just wanna know how to connect a general multiplexer in a simple circuit. I know which pins to connect to for what for this specific multiplexer, but I have no idea how to connect them. Sep 18, 2020 at 14:48
• You need to provide a high or low voltage to each of the inputs. The simplest way is to wire some of the inputs to power/Vdd and some to ground/Vss. That is not a very useful configuration though, as the outputs will be constant. Sep 18, 2020 at 14:54
• What are you trying to do, really? If your goal is to learn discrete digital circuits, what made you choose this path to learn? Sep 18, 2020 at 14:55
• @Justin, I don't want a useful configuration. Once I understand how to wire things up, I will start controlling the inputs. I just got my hands on a RPi and a bunch of electrical components so I want to make something. I have one other question on here where I explained what I wanna do and that's where someone suggested multiplexers. Sep 18, 2020 at 15:02

So the part you have is an CMOS dual one-of-four digital multiplexer.

With CMOS logic circuits you should tie every single one of the inputs on the chip to a valid logic level, either directly to a supply line or through a resistor.

The outputs can go somewhere (maybe a logic input or a resistor + LED, or even both if you keep the LED current low) or they can be left open.

An easy way to do that when you are playing with it on a solderless breadboard is to have a pullup or pulldown resistor such as 10K to a supply rail and use a switch to the opposite rail to control the input.

simulate this circuit – Schematic created using CircuitLab

The resistors R2 R3 are optional if you don't use a switch. R1 is required, otherwise SW1 would short out the power supply when closed. In the latter circuit the input is high with SW1 open and low with SW1 closed.

• This is exactly what I needed, thanks! Sep 18, 2020 at 15:06