Skip to main content

Relay

Introduction​

We know that the GPIO output level of our development board is 3.3V, which cannot directly control high-voltage devices such as lights (220V). This is where the relay — a commonly used low-voltage-controlled high-voltage component — comes in.

Objective​

Use a button to control the relay's on/off state.

Experiment Explanation​

The image below shows the 01Studio relay module, which can be powered by 3.3V. The WalnutPi PicoW's IO pins can be directly connected to the module's control terminal. The low-voltage control interface on the left mainly has power pins and a signal control pin (supply voltage is typically 3.3V, depending on the manufacturer's specifications). The blue high-voltage section on the right can connect to 220V appliances.

Note

Always use a 3.3V level controlled relay, because the WalnutPi PicoW's GPIO voltage tolerance is 3.3V. Using a 5V-controlled relay may back-feed and damage the development board.

relay

A relay can be understood as a switch, similar to a light switch panel in our homes, except now it's controlled by an MCU's GPIO. A typical wiring diagram for a relay controlling a high-voltage appliance from low voltage is shown below:

relay

In this experiment, WalnutPi PicoW pin 10 is connected to the relay module's control pin. The wiring diagram is as follows:

relay

The 01Studio relay module's control principle is very simple, similar to LED control: low level '0' means relay ON, high level '1' means relay OFF.

We can refer to the Basic Experiments — Button External Interrupt example for using the relay. Please see the External Interrupt chapter; it won't be repeated here!

The code flow is as follows:

Reference Code​

'''
Experiment Name: Relay
Version: v1.0
Author: WalnutPi
Platform: WalnutPi PicoW
Description: Use a button to change the relay's on/off state (external interrupt method)
'''

#Import related modules
from machine import Pin
import time

relay=Pin(10,Pin.OUT,value=1) #Build relay object, default off
KEY=Pin(0,Pin.IN,Pin.PULL_UP) #Build KEY object

state=0  #Relay pin state flag

#LED state toggle function
def fun(KEY):
    global state
    time.sleep_ms(10) #Debounce
    if KEY.value()==0: #Confirm button is pressed
        state = not state
        relay.value(state)

KEY.irq(fun,Pin.IRQ_FALLING) #Define interrupt, falling edge trigger

Experimental Results​

Run the code and you can control the relay on/off via the button:

relay

Relay control is very simple and widely applicable. It only requires a simple GPIO high/low level to achieve control.