CD74HC4067 16-channel multiplexer

Sixteen analog switches with one common pin, on a breakout.

Aliases: 74HC4067, 16-channel analog mux, SparkFun BOB-09056. Four address lines pick which channel is joined to COM, in either direction, so one analog pin reads sixteen knobs or sensors, or one pin drives sixteen outputs in turn.

Pins

Pin	What it does
I0 to I15	The sixteen channels.
COM	The common pin (SIG on some boards).
S0 to S3	The channel address, S0 the least significant bit.
EN	Enable, active low: tie it to ground, or high to open every switch.
VCC, GND	Supply, 2 to 6 V.

While it runs

The marker beside the channel joined to COM lights.

Reading it on an Arduino

const uint8_t ADDRESS[4] = {2, 3, 4, 5};   // S0 to S3

int readChannel(uint8_t ch) {
  for (uint8_t bit = 0; bit < 4; bit++) digitalWrite(ADDRESS[bit], (ch >> bit) & 1);
  delayMicroseconds(50);
  return analogRead(A0);                    // COM on A0
}

What the model gets right

From the TI datasheet:

It is a switch, not a buffer. The chosen channel is joined to COM through the on-resistance, both ways, so the signal is divided by whatever loads it, as on the bench.

The on-resistance: 70 ohm typical from 4.5 V up, 100 ohm from 3 V and 160 ohm below.

Every other channel is open, and EN high opens them all. An address line that is not a clean logic level opens every switch too.

What it does not model

The switching time, break-before-make, charge injection, leakage, the on-resistance's change with the signal voltage, and signals past the supply rails, which a real one clamps.

Common mistakes

Leaving EN unconnected: it floats, and the chip may or may not be enabled. Tie it to ground.

Reading straight after changing the address: give the switch and the ADC's input a few microseconds to settle.

See it in action

Mux knobs reads three potentiometers on one analog pin. Open it at /templates.