Water Level Sensor

This project uses an ESP32 on battery to measure the water level in a tank an reports it to a MQTT server over Wifi. It is meant to work on battery but can be used on USB power.

Hardware

• Lilygo T-OI (it should work with other ESP32-based boards but it has not been tested)
• Ultra Sonic module AJ-SR04M (for example here). It won't work with any other variant like AJ-SR04M-2

Optional:

• A 16340 battery
• Wifi antenna
• A solar panel to charge the battery

The sensor should be placed in the tank where it will not pick up a reading from other obstacle so mind the reading radius

Preparation and building

In this application, the distance sensor is used in Mode 2 (Low Power Consumption Mode), so a 330 kΩ resistor must be soldered on R19.

Rename config.cpp.sample to config.h and adapt the settings to your environment.

Software configuration

The software is configured over MQTT. You need to send a JSON message to the device on topic ROOT_TOPIC/config with configuration values. The possible settings are (case-sensitive):

• minValue (Default 200mm): the value read when there is no water in the tank. The sensor has a blind area of 20cm so the default value is as low has it can get. This ensures that the correct value is detected as the level in the tank changes.
• maxValue (Default 8000mm): the value read when the tank is full. The sensor cannot measure distamces of more than 8m.This ensures that the correct value is detected as the level in the tnak changes.
• sleepTime (Default 5s): the time between 2 readings in seconds. This setting has a huge impact on autonomy.
• sleepTimeOnPower (Default 5s): the time between 2 readings in seconds when dthe system is on USB power.
• onPowerThreshold (Default 3.5V): the threshold above which the sleepTimeOnPower sleep delay will be used instead of sleepTime.
• maxDifference (Default 200mm): the maximum difference allowed between 2 readings. If the difference is higher, another reading is performed.
• logLevel (Default 3): a value between 0 and 6 to define how much is logged.

Example:

{
  "minLevel": 400,
  "maxDifference": 15
}

If you configure more than one probe, you can use indexed minLevel and maxLevel:

{
  "minLevel[0]": 1000,
  "maxLevel[0]": 300,
  "maxLevel[1]": 250
}

Mind the quotes, punctuation and casing!

Make sure you send the config with the Retain option. The values are read at the end of the reading cycle so it will take up to 5 minutes for the settings to apply. To speed up the process, you can push the reset button to trigger a new cycle.

Getting log files

It is possible to get log files from previous run. Send the file name on ROOT_TOPIC/file/get (e.g. "/log001.txt"). The content is sent on the ROOT_TOPIC/file/data topic. You can also get a list of all the files by sending a folder name (typically "/") on ROOT_TOPIC/file/dirlist. The result is sent on ROOT_TOPIC/file/dir/FOLDER_NAME (i.e. if you requested the listing for the root folder, the answer would come on ROOT_TOPIC/file/dir/).

Remote update

You can update the firmware remotely by sending the url of the firmware on topic ROOT_TOPIC/update/url. Only works in http port 80 or using TFTP. On Linux, you can easily start a TFTP server using:

dnsmasq --port=0 --enable-tftp --tftp-root=/tmp --tftp-no-blocksize --user=root --group=root

Hardware setup

This is how you connect your ESP32: