This code is for a general purpose distance sensor, which can be used for monitoring things like water levels. For example, I use it to monitor my sump pump to make sure it doesn't overflow. It's configured to send warning text messages to me via Twilio when the water level gets too high:

Below are a list of materials and setup instructions you can use this code to monitor anything you want.

• Wireless capable Raspberry Pi with GPIO headers, power cord, and SD card
• Female to Female Jumper Wires
• An ultrasonic sensor, either US-100 or RCWL-1601.
• An internet connection to send text messages through Twilio's API

All told, the above materials should cost around $40.

The first step is to get the Raspberry Pi up and running and connect the distance sensor. I won't go in-depth into this as there are better resources out there but the crucial thing to know is that I assume that the echo of your sensor is attached to GPIO 17, and the trigger to GPIO 27. The power can be attached to any 3V pin, and the ground to any ground pin.

The next step is to put the sensor in position. Point the sensor at what you want to measure, keeping it perpendicular to the surface (these sensors use soundwaves to measure distances, so oblique angles won't work). The sensors will work at about 2cm to 450cm away, but 10cm-250cm will give you the best results.

All of the code for this project is available in this GitHub repository. Either ssh into your Raspberry Pi, or connect it to a keyboard or screen. Choose a directory to install this code, then clone and enter this repo:

$ git clone https://github.com/psthomas/distance-sensor.git
$ cd distance-sensor

Next, you need to install the dependencies, which I used a virtual environment for to keep consistent. The recommended way to create virtual environments is now the built in venv, so that's what I'll use:

$ python3 -m venv .venv
$ source .venv/bin/activate
$ pip3 install requirements.txt

Next, you need to set up the configuration file as outlined below. Once that's finished, come back here for the final commands to get it up and running.

The final thing to do is tell your computer to routinely run this script to take a distance measurement. There's a small script in the root directory called run.sh that's used for this purpose. All you need to do is open it and change the path /home/pi/Projects/depth-sensor to whatever path your project is installed at.

#!/bin/bash

cd /home/pi/Projects/distance-sensor
source .venv/bin/activate # Activate Python environment
python3 sensor.py # Run the sensor code

Then use crontab to add this script as a routinely repeating Cron job using this command:

$ crontab -e

This will open up a file for editing which you can then add a job to. You can choose any interval that suits you, but I chose to run it every minute using the line below (any frequency less than a minute probably isn't a good idea). Note that you should change the path /home/pi/Projects/distance-sensor/run.sh to point wherever the script is located on your device:

*/1 * * * * /bin/bash /home/pi/Projects/distance-sensor/run.sh

After you save and close the Cron file, the script will be up and running at the interval you specified. A results.csv file will then be created in the top directory to record the distance measurements, and any logging outputs from sensor.py will be recorded in sensor.log in the same directory.

There's an example_config.json file in the top directory that shows a complete configuration. You need to add a config.json file in this same directory, which is the actual file that will be read in by sensor.py. Note that this file will contain sensitive information like your Twilio authorization token, so it should never be included in version control (it's already in the .gitignore file for this reason).

To complete the configuration file, you need to first create a Twilio account and get a phone number. You then need to find your Account SID and Auth Token on the Twilio dashboard and place them in the appropriate fields in config.json.

{
  "name": "sump pump",
  "type": "near",
  "warning_distance": 15.5,
  "warning_frequency": 15,
  "twilio_number": "+15017122661",
  "phone_numbers": ["+15017122661","+15017122661"],
  "twilio_account_sid": "ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
  "twilio_auth_token": "your_auth_token"
}

The configuration options are explaned below:

• name: This string is the title of your sensor, and it will be referenced in any SMS notifications you get so you can distinguish between this sensor and others you may have installed.

• type: This string represents the sensor type. There are three options: near, far or static. A near type sensor will send a warning whenever a measurement is closer than the warning distance to the sensor. A far type sensor will warn you if a measurement is further away than the warning distance. And a static sensor defines an upper and lower bound that the measurement must be between.

• warning_distance: In centimeters, this setting represents the distance from the sensor that triggers a warning message. This will always be a positive distance because it is measured relative to the sensor. For the near and far sensors, this value will be an integer or float. For static sensors, this value will be represented by an object like {"lower": 25, "upper": 50} that sets the bounds for the measurement.

• warning_frequency: How often, in minutes, the warning should be sent if a measurement warrants a warning. This is to prevent your phone from getting blown up by warnings after you've already received one.

• twilio_number: A string representing the number you've purchased from Twilio.

• phone_numbers: A list of one or more phone numbers that will recieve the warning message. These phone numbers should be strings.

• twilio_account_sid: A string of the account_sid from your Twilio dashboard.

• twilio_auth_token: A string of the authorization token from your Twilio dashboard.

Here are a few more configuration examples. The first is for monitoring the water in a christmas tree stand. The water level will be getting further away from the sensor as it drains, so it has a far type sensor.

{
  "name": "christmas tree",
  "type": "far",
  "warning_distance": 10,
  "warning_frequency": 15,
  "twilio_number": "+15017122661",
  "phone_numbers": ["+15017122661"],
  "twilio_account_sid": "ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
  "twilio_auth_token": "your_auth_token"
}

The final configuration is for monitoring if a garage door is open. It uses a static type sensor:

{
  "name": "garage door",
  "type": "static",
  "warning_distance": {"lower": 30, "upper": 100},
  "warning_frequency": 15,
  "twilio_number": "+15017122661",
  "phone_numbers": ["+15017122661"],
  "twilio_account_sid": "ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
  "twilio_auth_token": "your_auth_token"
}