Category: raspberrypi

Switch relay with Raspberry pi + Arduino Uno

The 5V Relay switch require that i have require around 52mA current to work properly.

  • Raspberry pi max GPIO current with 5v Relay = ?
  • Arduino pin 13 current with 5v Relay = 38.5mA
  • Arduino pin 13 + 12 current with 5v Relay = 45 mA
  • Arduino pin 13 + 12 + 2 current with 5v Relay = 47.3 mA ( This worked )

So Now i can use Arduino as a switch on/off. Also I needed this switching to be based on some external events. So I used Aurdino Pin 2 as INPUT pin and added one 2.7K ohm resistor to from pin2 to Ground.

int status = 0;

void setup() {
  pinMode(13, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(2, INPUT);
}

void loop() {
  status = digitalRead(2);
  if (status == HIGH) {
    digitalWrite(13, HIGH);
    digitalWrite(12, HIGH);
    digitalWrite(8, HIGH);
  }
  else {
    digitalWrite(13, LOW);
    digitalWrite(12, L0W);
    digitalWrite(8, LOW);
  }
}

Switch ON = 7PM
Switch OFF = 12AM

  • added Cronjob on Raspberry Pi 4
0 19 * * * /usr/bin/python3.8 /opt/led.py on
0 0 * * * /usr/bin/python3.8 /opt/led.py on

led.py

import RPi.GPIO as GPIO
from time import sleep 
import sys

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(21, GPIO.OUT, initial=GPIO.LOW)

if sys.argv[1] == "on":
    GPIO.output(21, GPIO.HIGH)
    #print("on")
    exit()
elif sys.argv[1] == "off":
    GPIO.output(21, GPIO.LOW)
    #print("off")
    exit()

Raspberry Pi Max current with GPIO for LED

Note: withdrawing more current(~15mA) from GPIO can affect the Rpi
https://raspberrypi.stackexchange.com/questions/9298/what-is-the-maximum-current-the-gpio-pins-can-output

  • Use 5V Pin (2,4)
  • Use GPIO as Negative volt
  • Max current withdrawn was 23mA for my use case
import RPi.GPIO as GPIO
from time import sleep 
import sys

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(21, GPIO.OUT, initial=GPIO.HIGH)

if sys.argv[1] == "on":
    GPIO.output(21, GPIO.LOW)
    #print("on")
    exit()

Fore More brightness:

  • Add multiple GPIO as GROUND
  • After adding GPIO20 as ground it was taking ~18mA from GPIO20
  • And Overall of ~36mA from both GPIO 20 and 21

Raspberry pi 4 to measure temperature and humidity with DHT11/DHT22 sensor

pip3 install adafruit-circuitpython-dht
apt-get install libgpiod2

temp.py

import Adafruit_DHT
import time
 
DHT_SENSOR = Adafruit_DHT.DHT11
DHT_PIN = 4

#while loop is there because sometime it does not get the temp.
while True:
    humidity, temperature = Adafruit_DHT.read(DHT_SENSOR, DHT_PIN)
    if humidity is not None and temperature is not None:
        print("Temp={0:0.1f}C Humidity={1:0.1f}%".format(temperature, humidity))
    else:
        print("Sensor failure. Check wiring.");
    time.sleep(1);

run:

python3 temp.py

For DHT22 sensor:

temp-dht22.py

import Adafruit_DHT
import time

DHT_SENSOR = Adafruit_DHT.DHT22
DHT_PIN = 4

humidity, temperature = Adafruit_DHT.read(DHT_SENSOR, DHT_PIN)
if humidity is not None and temperature is not None:
    #print("Temp={0:0.1f}C Humidity={1:0.1f}%".format(temperature, humidity))
    print("{0},{1}".format(temperature, humidity))
  • shell script to send over pushgateway
root@lp-arm-1:~# cat /opt/cron/get_temp_dht22.sh
#!/bin/bash

t_and_h=$(python3 /opt/cron/get_temp_dht22.py)

temprerature=$(echo $t_and_h | awk -F ',' '{print $1}')
humidity=$(echo $t_and_h | awk -F ',' '{print $2}')
echo "room_temp $temprerature" | curl --data-binary @- http://192.168.0.183:30008/metrics/job/room_temp/instance/lp-arm-1
echo "room_humidity $humidity" | curl --data-binary @- http://192.168.0.183:30008/metrics/job/room_humidity/instance/lp-arm-1

raspberry pi 4 wifi setup using command line only – bash

  • find the wifi adaptor name
lshw

ls /sys/class/net

it was wlan0 in my case

  • edit /etc/netplan/50-cloud-init.yaml
network:
    ethernets:
        eth0:
            dhcp4: true
            optional: true
    version: 2
    wifis:
        wlan0:
            optional: true
            access-points:
                    "SSID-NAME":
                            password: "your_password"
            dhcp4: yes
  • Test the config
netplan try
netplan --debug try

This command will make the above changes for 120seconds if anything wrong it will be reverted back. OR you can hit Enter to make the changes.

  • apply config
netplan generate 
netplan apply
#enable wifi module

modprobe brcmfmac

#disable
modprobe -rv brcmfmac


nano /etc/modprobe.d/raspi-blacklist.conf

blacklist brcmfmac
blacklist brcmutil
  • Stop wifi without reboot
#disable
rfkill block wifi


#enable
rfkill unblock wifi
  • Using NMCLI
nmcli d

nmcli d wifi list

nmcli d wifi connect my_wifi password <password>

#### with BSSID
root@lp-arm-3:~# nmcli device wifi list
IN-USE  BSSID              SSID            MODE   CHAN  RATE        SIGNAL  BARS  SECURITY  
        xx:06:C3:CD:57:xx  TP-Link_123    Infra  153   270 Mbit/s  100     ▂▄▆█  WPA2      
*       xx:06:C3:CD:57:xx  TP-Link_123    Infra  2     130 Mbit/s  93      ▂▄▆█  WPA2 

====================
nmcli d wifi connect xx:06:C3:CD:57:xx password PASSWORD

More : https://raspberrypi.stackexchange.com/questions/108636/setting-wifi-up-via-the-command-line-ubuntu-server-18-04-4-lts-raspberry-pi-4

https://huobur.medium.com/how-to-setup-wifi-on-raspberry-pi-4-with-ubuntu-20-04-lts-64-bit-arm-server-ceb02303e49b

https://ubuntu.com/core/docs/networkmanager/configure-wifi-connections