Capacitance Liquid Level Sensor

*** As of October 2022, this project is on hold for me due to winter weather. Work is expected to resume Spring 2023. ***

The goal of this project is to determine the level of a liquid inside of a tank without making direct contact with that liquid. While the intent of this project is aimed at improving the monitoring of RV holding tanks with the use of HomeAssistant, this type of liquid level measurement can also be used in a variety of other applications.

Please note that I am having some difficulties getting readings on my RV tanks. Graphs and data used in this repo are from small-scale test containers (<=15 gallons), including glass and hard plastic. Initial tests were overwhelmingly positive, however the RV application portion of this project is still very much a work in progress. Results will vary based on tank material and thickness. This project should work, considering there are products on the market that do the exact same thing (SeeLevel, for example). If you have any interest in collaboration, please reach out to me.

Ideas for Large Scale Use (>20 gallons) On RV Tanks

Untested ideas that have been suggested by others.

• Add 3v, 5v, or 12v across the strips to increase the electromagneic field between the strips. Could help with thicker tanks less conductive materials.
• Decrease the distance between the adhesive strips
• Decrease length of wire between adhesive strips and ESP32
• Increase thickness of strips
• Add additional copper strips

How does it work?

This project uses the concept of electromagnetic fringe fields and capacitance to determine the current level of a liquid inside of a tank without making direct contact. Liquid is an electrical conductor. When two conductive materials are placed side-by-side, a "fringe" effect is created. As the level of the liquid increases, the "fringe" decreases. Therefore, metal tanks or tanks with metal cages will not work. It is recommended that you use plastic or fiberglass tanks ¼" thick or less.

Materials Needed

• NodeMCU ESP32 or ESP8266

• Breadboard Jumper Wires

• 2-Inch Aluminum HVAC Tape

• 1-Inch Copper Adhesive Tape

• Plastic or fiberglass tank

• Secondary Container with a known liquid quantity (such as a 1 gallon jug)

• Sewer connection during tank calibration is highly recommended

Instructions

Each setup is based on the tank, the type of liquid being measured, and the amount of additional noise picked up by the ESP device. Results may vary.

1. Determine the size of your holding tank in gallons. This will be needed later on.

2. Setup the ESP32 by placing a jumper wire on P12 (or whichever pin is equivalent to Touch 4), and another one on a GND. A single ESP32 can monitor as many tanks as there are Touch GPIOs available. The ESP32 will need to be powered via 5v to ensure adequate capacitance values.
   
   **IMPORTANT: The use of GPIOs 0, 2, 4, 5, 12, and 15 will result in a "strapping pin" error during setup. Avoid these pins if possible.

TANK SETUP

3. Cut 2 identical strips of aluminum tape so that they reach from the bottom to the top of your tank.. Clean the side of the tank and apply the pieces of tape 1-½" to 2" apart. *Based on your readings in future steps, the distance between the strips can be adjusted to facilitate better capacitance readings if needed.
   
   
   
   

4. Cut four 2-inch strips of copper tape and place them in the center of the strip, forming a roughly 2"x2" square with a slight overlap. Where the pieces overlap, place one of the GPIO jumper wires and secure. Ensure there is good contact with the copper tape.
   
   *Additional copper strips may be needed to secure the wire.
   
   
   
   
   
   

5. Open HomeAssistant, navigate to ESPHome, and follow the directions to setup your ESP32. Once initial setup is complete, copy the code found above and paste it below "captive_portal". Make adjustments to correlate with your specific device as needed.

   This code creates 2 sensors in HomeAssistant. The first is the straight capacitance value taken from the log which is needed for setup and can be used for debugging later on. The second sensor maps the capacitance values to the desired percentage values which will be gathered in the next step. An example yaml dashboard is provided.

   *Please note this example dashboard uses the ApexCharts card.

TANK CALIBRATION

*Before proceeding, the tanks involved will need to be emptied. It is recommended that you flush your black tank if able to do so in order to get the most accurate baseline readings.

6. For each tank you choose to monitor, calibration is required. Calibration requires a container with a known volume (1 gallon milk jug, 5 gallon bucket, etc). To calibrate your Sensor, start with your tank empty and record the capacitance value. Then, fill the tank with your container and record each value (for example, a 50 gallon tank being filled with a 1 gallon milk jug will have 50 values.) Remember, the more data points you have here, the more accurate your sensor will be.

   You will need to convert gallons into percent so you can properly map the values. For example, a 50 gallon tank is 50% full with 25 gallons. It is approximately 25% full with 12.5 gallons.
   This is an example of how I recorded my data. The graph is not needed.
   
   
   
   

7. With the capacitance values recorded, open ESPHome and edit the code, adding in your capacitance values and their corresponding percentage under "datapoints:". Update your ESP32 and test your current calibration. If values appear incorrect, repeat step 7 and adjust datapoints accordingly.

   Datapoints should be in the following format:

   • Capacity Reading -> Mapped Percent
   • 426 -> 37

8. Once a good accuracy is achieved, change the sensor update rate in ESPHome from 3 seconds to your preferred rate, such as 15 minutes.

That's it! You should now have a working non-contact liquid level sensor that can be used throughout your HomeAssistance instance.

Special thanks to all of those who assisted in any aspect of this project.