Using the CD74HC4067 Multiplexer with the Raspberry Pi

The CD74HC4067 is a 16-channel analog/digital multiplexer that enables a Raspberry Pi to interface with up to 16 inputs or outputs using only a few GPIO pins. It’s perfect for expanding the I/O capabilities of your Raspberry Pi when working with multiple sensors or devices.

---

What You Will Need

1. Raspberry Pi (any model with GPIO support, e.g., Pi 3, Pi 4)
2. CD74HC4067 Multiplexer
3. Analog or Digital Input Devices (e.g., sensors, switches)
4. Breadboard and Jumper Wires
5. Python installed on the Raspberry Pi

---

Step 1: Understanding the CD74HC4067

The CD74HC4067 has:

• 16 Input/Output Channels (S0-S15)
• 4 Control Pins (S0, S1, S2, S3) to select the active channel.
• 1 Enable Pin (EN) to activate the multiplexer (active LOW).
• A single COM (common) pin for shared communication.

Truth Table for Channel Selection

S3	S2	S1	S0	Active Channel
0	0	0	0	S0
0	0	0	1	S1
0	0	1	0	S2
...	...	...	...	...
1	1	1	1	S15

---

Step 2: Wiring the CD74HC4067 to the Raspberry Pi

Connect the multiplexer to the Raspberry Pi as follows:

CD74HC4067 Pin	Raspberry Pi Pin
VCC	3.3V (Pin 1)
GND	GND (Pin 6)
S0	GPIO17 (Pin 11)
S1	GPIO27 (Pin 13)
S2	GPIO22 (Pin 15)
S3	GPIO23 (Pin 16)
EN	GND (Active LOW)
COM	GPIO18 (Pin 12, Analog Input/Output)
S0-S15	Connect sensors/devices

---

Step 3: Install Required Libraries

Update your Raspberry Pi and install Python libraries for GPIO control.

sudo apt update && sudo apt upgrade -y
sudo apt install python3-rpi.gpio

---

Step 4: Python Code to Read Data from the Multiplexer

Here’s a Python script to control the CD74HC4067 and read data from the connected channels.

Python Code Example

import RPi.GPIO as GPIO
import time

# Define GPIO pins
S0 = 17
S1 = 27
S2 = 22
S3 = 23
COM = 18  # Common pin for input/output

# Initialize GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup([S0, S1, S2, S3], GPIO.OUT)
GPIO.setup(COM, GPIO.IN)  # Set COM pin as input for reading data

# Function to select a channel
def select_channel(channel):
    GPIO.output(S0, channel & 0x01)
    GPIO.output(S1, (channel >> 1) & 0x01)
    GPIO.output(S2, (channel >> 2) & 0x01)
    GPIO.output(S3, (channel >> 3) & 0x01)

try:
    while True:
        for channel in range(16):
            select_channel(channel)
            time.sleep(0.1)  # Small delay for channel stabilization
            value = GPIO.input(COM)  # Read data from the active channel
            print(f"Channel {channel}: {value}")
        time.sleep(1)
except KeyboardInterrupt:
    print("Exiting...")
finally:
    GPIO.cleanup()

---

Step 5: Applications of the CD74HC4067 with Raspberry Pi

1. Reading Multiple Sensors: Interface with up to 16 sensors (e.g., temperature, humidity, or light).
2. Expanding Digital I/O: Manage multiple switches, LEDs, or relays.
3. Analog Sensor Integration: Read signals from potentiometers, joysticks, or soil moisture sensors.
4. Home Automation: Control multiple devices like lights, fans, or appliances.

---

Troubleshooting

1. No Data from Channels:

   • Verify the wiring of S0-S3 control pins and the COM pin.
   • Ensure sensors/devices are properly connected to the S0-S15 pins.

2. Incorrect Channel Selection:

   • Check the truth table for S0-S3 configurations.
   • Ensure the EN pin is connected to GND for activation.

3. Intermittent Readings:

   • Add a small delay (time.sleep(0.1)) between switching channels to allow signal stabilization.

---

Conclusion

The CD74HC4067 multiplexer is a powerful and cost-effective way to expand the Raspberry Pi’s input/output capabilities. By following this guide, you can easily interface with up to 16 analog or digital devices using just 4 GPIO pins. Experiment with various sensors and applications to make the most of this versatile module! 🚀