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I am doing a small project which consists of turning LEDs on and off using the GPIO library. I am able to successfully turn the LED's on and off using a browser on my laptop. But now I want the LEDs to turn on automatically at a specified time for a short duration.
Example: If I set the LED's to turn on after 12:00 for 2 hours, then the Raspberry Pi would automatically turn them on at 12:00 for 2 hours.
Is this possible, and if so, how?
Let's break this answer in two parts: scheduling a task and turning a led on and off, than wrap together. You can go to the end and just get the script if you prefer!
So I would suggest you use the atd for one time scheduling in Raspbian. If you need something repetitive, use cron - I will cover here only how to use the at command. More details here: https://debian-handbook.info/browse/stable/sect.task-scheduling-cron-atd.html
First, you need to install it!
sudo apt-get install at
Now for using it, see the date right now on your raspbian - I'm assuming you are connected to it using ssh or is accessing through the terminal.
date
Let's make a blank folder on your home for testing purpose
mkdir ~/test
cd ~/test
Let's schedule a job!!
echo "echo \"teste\" > ~/test/test.log " | at 10:52
Let's wait it to be executed!!!
watch ls
The watch command will execute the command after it repeatedly and will output it's output with a clock, so we can confirm it works! (an archive named test.log be created at the scheduled time.
Now you need to make a script to turn on and off a LED - I don't know how you are doing this and schedule it with using the at command. We will use the gpio utility from wiringpi. Let's learn about it.
sudo apt-get install wiringpi
I will suppose you want to turn on and off led 5, but do whatever you want. Let's test if it works. Try:
gpio -g mode 5 out
gpio -g write 5 1
You can turn the led off using:
gpio -g write 5 0
Ok, now we need to wrap all of this in a bash script for ease of use.
Let's create ledsched.sh:
#!/bin/bash
timeat="$1"
duration="$2"
ledpin="$3"
endtime=`date +%H:%M -d " $timeat today + $duration"`
gpio -g mode $ledpin out
echo "gpio -g write $ledpin 1" | at $timeat
echo "gpio -g write $ledpin 0" | at $endtime
And call it using (remember to use first chmod +x ledsched.sh ):
./ledsched.sh 12:00 2hours 5
I'm scheduling to turn pin 5 on at 12:00 and off after 2 hours. If your led is at pin 5 it should work!
Oh, if you do have access to the visual interface, you can use the alarm-clock-applet. Install it from the command line with sudo apt-get install alarm-clock-applet .
To start, you need to make sure that your Raspberry Pi is connected to the internet. This is needed to track time. Then type in this code:
import RPi.GPIO as GPIO
import datetime
import time
pin = your_output_pin_here
GPIO.setup(pin, GPIO.OUT)
while True:
time = datetime.datetime.now().strftime("%H:%M")
if time == "12:00":
GPIO.output(pin, True)
time.sleep(number_of_seconds_for_led_to_be_on_here)
GPIO.output(pin, False)
time.sleep(0.030)
Replace things like 12:00 and your_output_pin_here with your own values. Every 30 milliseconds, it checks whether it is 12:00. If it is, it turns on the LED. It then waits a number of seconds, then turns it back off.
If you want this program to be run whenever you start the Raspberry Pi, go into LXTerminal and type this:
sudo crontab -e
It will open a text document. Use the arrow keys to navigate to the bottom, then type this:
@reboot sudo python /path/to/your/python/file.py &
Replace "/path/to/your/python/file.py" with the path to your python file (like /home/pi/timed_led.py). Do CTRL+O and RETURN to save. Then to exit, do CTRL-X.
When you start up your Pi, it will take a while to boot up, then it will run the program. If you ever want to stop it doing this, then do sudo crontab -e again and put a hash (SHIFT+3) at the front of the line.
I really hope this helps!
