Raspberry Pi - Keypad - Relay
This tutorial instructs you how to combine a keypad, relay, and Raspberry Pi. If the user enters the correct password on the keypad, the Raspberry Pi will turn on the relay.
The tutorial also provides the Raspberry Pi code which activates a relay over a certain period of time and then deactivates it. Moreover, the Raspberry Pi code is capable of handling multiple passwords.
By connecting a relay to an Electromagnetic Lock, Solenoid Lock, Linear Actuator, Heating Element, Pump, or Fan... We can then control them using a keypad.
Hardware Preparation
| 1 | × | Raspberry Pi 4 Model B | |
| 1 | × | Keypad | |
| 1 | × | Relay | |
| 1 | × | Jumper Wires | |
| 1 | × | (Optional) Screw Terminal Adapter for Raspberry Pi |
Or you can buy the following sensor kits:
| 1 | × | DIYables Sensor Kit (30 sensors/displays) | |
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
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Overview of Keypad and Relay
If you are unfamiliar with keypad and relay (including pinout, functionality, programming, etc.), the following tutorials can help:
- Raspberry Pi - Keypad tutorial
- Raspberry Pi - Relay tutorial
Wiring Diagram
This image is created using Fritzing. Click to enlarge image
Raspberry Pi Code - turn relay on if the password is correct
Detailed Instructions
- Make sure you have Raspbian or any other Raspberry Pi compatible operating system installed on your Pi.
- Make sure your Raspberry Pi is connected to the same local network as your PC.
- Make sure your Raspberry Pi is connected to the internet if you need to install some libraries.
- If this is the first time you use Raspberry Pi, See how to set up the Raspberry Pi
- Connect your PC to the Raspberry Pi via SSH using the built-in SSH client on Linux and macOS or PuTTY on Windows. See to how connect your PC to Raspberry Pi via SSH.
- Make sure you have the RPi.GPIO library installed. If not, install it using the following command:
sudo apt-get update
sudo apt-get install python3-rpi.gpio
- Create a Python script file keypad_relay.py and add the following code:
# This Raspberry Pi code was developed by newbiely.com
# This Raspberry Pi code is made available for public use without any restriction
# For comprehensive instructions and wiring diagrams, please visit:
# https://newbiely.com/tutorials/raspberry-pi/raspberry-pi-keypad-relay
import RPi.GPIO as GPIO
import time
# Define keypad layout
KEYPAD = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9],
['*', 0, '#']
]
# Define GPIO pins for rows, columns, and relay
ROW_PINS = [17, 27, 22, 24]
COL_PINS = [25, 8, 7]
RELAY_PIN = 16 # Adjust this to the actual GPIO pin connected to the relay
# Password to unlock
PASSWORD = [1, 2, 3, 4]
# Initialize GPIO
GPIO.setmode(GPIO.BCM)
# Set up row pins as inputs with pull-up resistors
for row_pin in ROW_PINS:
GPIO.setup(row_pin, GPIO.IN, pull_up_down=GPIO.PUD_UP)
# Set up column pins as outputs
for col_pin in COL_PINS:
GPIO.setup(col_pin, GPIO.OUT)
GPIO.output(col_pin, GPIO.HIGH)
# Set up relay pin as an output
GPIO.setup(RELAY_PIN, GPIO.OUT)
GPIO.output(RELAY_PIN, GPIO.LOW) # Initially, keep the relay off
def get_key():
key = None
# Scan each column
for col_num, col_pin in enumerate(COL_PINS):
GPIO.output(col_pin, GPIO.LOW)
# Check each row
for row_num, row_pin in enumerate(ROW_PINS):
if GPIO.input(row_pin) == GPIO.LOW:
key = KEYPAD[row_num][col_num]
# Wait for key release
while GPIO.input(row_pin) == GPIO.LOW:
time.sleep(0.05)
GPIO.output(col_pin, GPIO.HIGH)
return key
def check_password(input_password):
return input_password == PASSWORD
entered_keys = []
try:
while True:
pressed_key = get_key()
if pressed_key is not None:
print(f"Pressed: {pressed_key}")
if pressed_key == '*':
entered_keys = [] # reset the input password
elif pressed_key == '#':
if check_password(entered_keys):
print("Password correct! Access granted.")
GPIO.output(RELAY_PIN, GPIO.HIGH) # Activate the relay
break
else:
print("Incorrect password. Try again.")
entered_keys = [] # reset the input password
else:
entered_keys.append(pressed_key)
time.sleep(0.1)
except KeyboardInterrupt:
GPIO.cleanup()
- Save the file and run the Python script by executing the following command in the terminal:
python3 keypad_relay.py
- Enter 9765 followed by the # key, then 1234 followed by the # key.
- Check the Terminal for the result and the state of the relay.
PuTTY - Raspberry Pi
The incorrect password! try again
The correct password! Turning ON relay
The script runs in an infinite loop continuously until you press Ctrl + C in the terminal.
Code Explanation
Authorized passwords are pre-defined in the Raspberry Pi code. A string is used to store the password inputted by users, called input string. In keypad, two keys (* and #) are used for special purposes: clear password and terminate password. When a key on keypad is pressed:
- If the pressed key is not two special keys, it is appended to the input string.
- If the pressed key is *, the input string is cleared. This can be used to start or re-start inputing the password.
- If the pressed key is #:
- The Raspberry Pi verifies if input string match one of the pre-defined passwords, the relay is turned on.
- Regardless of whether the password is correct or not, the input string is cleared for the next input.
Raspberry Pi Code - turn a relay on in a period of time if the password is correct
If the password is correct, the relay will be turned on for 5 seconds. After that period of time, it will be switched off.
# This Raspberry Pi code was developed by newbiely.com
# This Raspberry Pi code is made available for public use without any restriction
# For comprehensive instructions and wiring diagrams, please visit:
# https://newbiely.com/tutorials/raspberry-pi/raspberry-pi-keypad-relay
import RPi.GPIO as GPIO
import time
# Define keypad layout
KEYPAD = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9],
['*', 0, '#']
]
# Define GPIO pins for rows, columns, and relay
ROW_PINS = [17, 27, 22, 24]
COL_PINS = [25, 8, 7]
RELAY_PIN = 16 # Adjust this to the actual GPIO pin connected to the relay
# Password to unlock
PASSWORD = [1, 2, 3, 4]
# Initialize GPIO
GPIO.setmode(GPIO.BCM)
# Set up row pins as inputs with pull-up resistors
for row_pin in ROW_PINS:
GPIO.setup(row_pin, GPIO.IN, pull_up_down=GPIO.PUD_UP)
# Set up column pins as outputs
for col_pin in COL_PINS:
GPIO.setup(col_pin, GPIO.OUT)
GPIO.output(col_pin, GPIO.HIGH)
# Set up relay pin as an output
GPIO.setup(RELAY_PIN, GPIO.OUT)
GPIO.output(RELAY_PIN, GPIO.LOW) # Initially, keep the relay off
def get_key():
key = None
# Scan each column
for col_num, col_pin in enumerate(COL_PINS):
GPIO.output(col_pin, GPIO.LOW)
# Check each row
for row_num, row_pin in enumerate(ROW_PINS):
if GPIO.input(row_pin) == GPIO.LOW:
key = KEYPAD[row_num][col_num]
# Wait for key release
while GPIO.input(row_pin) == GPIO.LOW:
time.sleep(0.05)
GPIO.output(col_pin, GPIO.HIGH)
return key
def check_password(input_password):
return input_password == PASSWORD
entered_keys = []
try:
while True:
pressed_key = get_key()
if pressed_key is not None:
print(f"Pressed: {pressed_key}")
if pressed_key == '*':
entered_keys = [] # reset the input password
elif pressed_key == '#':
if check_password(entered_keys):
print("Password correct! Access granted.")
GPIO.output(RELAY_PIN, GPIO.HIGH) # Activate the relay
time.sleep(5) # Wait for 5 seconds
GPIO.output(RELAY_PIN, GPIO.LOW) # Deactivate the relay
break
else:
print("Incorrect password. Try again.")
entered_keys = [] # reset the input password
else:
entered_keys.append(pressed_key)
time.sleep(0.1)
except KeyboardInterrupt:
GPIO.cleanup()