You can find the first part on how to built a water level sensor, here:
-Raspberry Pi with
Sendmail or postfix if you want a email warning.
What the software will do:
The command part
This part is invisible to the user and is (and should be ) independent of the webpage.
Using cron, it will read the water level every minute and save the information to a file. If the water level reaches a certain level, an email will be sent. This is the most important part.
The Web page
In this part, the web page reads the information from the file written by the cron job and displays an image of your pit.
Step 1: Download and copy the software
Download the zip file and uncompress it to the webfolder of your Raspberry. I recommend creating a subfolder at the root of your www folder. Typically, the folder path is /var/www/sumppump.
Step 2: Ajust the preferences
Save and close the file.
Open the file "preference.php". All the preferences are explained in the comments.
The $levelamber and $levelred variables change the color of the led on the webpage and sends an email to the $to variable.
Be careful: If you set the $preferunit to cm, be sure to set all other measements to cm. The same thing applies in reverse cms to inches."
Refer to this images for the definition of some variables
Step 3: Schedule the cron task
Add this line to your crontab file:
* * * * * php /var/www/sumppump/chklevel.php
This will instruct to run the php script at every minutes of every hour of every...
Save the file with ctrl-o and ctrl-x to close the file.