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# CD4051 8-Channel Analog Mux with an Arduino Uno

Powered from the Arduino Uno's 5V, the CD4051 needs 3.5 V on its select pins to see a high, which the Uno's 5 V outputs on D2, D3 and D4 provide directly. Its common pin goes to A0, turning one of the Uno's six analog inputs into eight.

## Wiring

| CD4051 8-Channel Analog Mux | Arduino Uno | Note |
| --- | --- | --- |
| VDD | 5V |  |
| VSS | GND |  |
| VEE | GND |  |
| INH | GND |  |
| A | D2 |  |
| B | D3 |  |
| C | D4 |  |
| COM | A0 |  |

## What to know on the Arduino Uno

- At VDD = 5 V the select inputs need at least 3.5 V for a high. The Uno drives 5 V, so it can select channels directly; a 3.3 V board could not with the mux on 5 V. (TI CD4051B datasheet SCHS047O, p. 8)
- The ATmega328P's ADC is designed for sources of about 10 kΩ or less. The mux adds 470 Ω typical (1050 Ω max) at 5 V in series, so 10 kΩ potentiometers stay within that; higher-impedance sources need a slower read or a buffer. (TI CD4051B datasheet SCHS047O, p. 6; Microchip ATmega328P datasheet DS40002061B, ADC section)
- Address to signal takes 720 ns at most at 5 V. The sketch waits 10 µs after setting the select pins, which also lets the Uno's sample-and-hold settle to the new channel before analogRead(). (TI CD4051B datasheet SCHS047O, p. 8)
- Every channel must stay between GND and the mux's 5 V supply, which is also the Uno's ADC range. A second CD4051 on A1 sharing D2 to D4 gives 16 inputs from four Uno pins. (TI CD4051B datasheet SCHS047O, p. 19)

## Code

```cpp
// CD4051 8-Channel Analog Mux on Arduino Uno: wiring and a free simulation at https://www.tinkered.ai/components/cd4051-multiplexer/arduino-uno
#include <Arduino.h>

const int SEL_A = 2;
const int SEL_B = 3;
const int SEL_C = 4;
const int MUX_COM = A0;

int readChannel(int ch) {
  digitalWrite(SEL_A, ch & 1);
  digitalWrite(SEL_B, (ch >> 1) & 1);
  digitalWrite(SEL_C, (ch >> 2) & 1);
  delayMicroseconds(10);   // the switch settles (about 0.5 µs at 5 V)
  return analogRead(MUX_COM);
}

void setup() {
  Serial.begin(115200);
  pinMode(SEL_A, OUTPUT);
  pinMode(SEL_B, OUTPUT);
  pinMode(SEL_C, OUTPUT);
}

void loop() {
  Serial.print("pot 1: ");
  Serial.print(readChannel(0));
  Serial.print("  pot 2: ");
  Serial.println(readChannel(1));
  delay(200);
}
```

Compiled for arduino:avr:uno on 2026-10-29.

## Questions

### Can I use a CD4051 with an Arduino Uno to read more analog inputs?

Yes. Power it from the Uno's 5V, drive A, B and C from three digital pins and read COM on an analog pin: each CD4051 turns one Uno analog input into eight.

### Do the CD4051 select pins work with the Uno's 5 V logic?

Yes. With the mux on 5 V, a select high needs 3.5 V minimum (TI datasheet, p. 8), and the Uno drives its pins to 5 V.

### Why are my CD4051 readings on the Uno mixed up between channels?

The ADC needs a moment after the channel changes. Wait a few microseconds after setting A, B and C, as the sketch does with delayMicroseconds(10), and keep source impedance around 10 kΩ or less; you can also discard the first analogRead() after a switch.

## More

- [CD4051 8-Channel Analog Mux reference](https://www.tinkered.ai/components/cd4051-multiplexer.md): pinout, specs, rules and common mistakes

## Try it

Tinkered simulates the CD4051 8-Channel Analog Mux on the Arduino Uno in the browser, with this wiring and code, free: https://www.tinkered.ai/components/cd4051-multiplexer/arduino-uno