Hi
Can anyone recommend any liquid level sensors for Arduinos that are able to detect soap? I need a sensor (preferably 3V) that would be able to sense if there is soap left in the dispenser. The dispenser is made of plastic, so something that would not be submerged. I found this Gravity: Non-contact Capacitive Flexible Liquid Level Sensor(5V)-DFRobot, but has anyone tried something like this with any other liquid other than water? Will it work?
I can't use a sensor for distance since I have no room in the container and some of the dispensers are closed plastic bottles.
If the container is clear you could try some some optical sensor method with the container between sensor and transmitter.
Or, maybe a rain sensor- How Does a Windshield Rain Sensor Work? | True Blue Auto Glass
This seems hopeless. If you can't put anything inside, and you can't see inside, what kind of magic are you hoping for? If the bottles are transparent, you have some hope of using optical detection as mentioned, but the problem would be to make it reliable, you have to emit, focus and detect a beam and have reliable luminance thresholds for detection. Soap will have foam or bubbles, right? Sticky goo sticking to the inside of the bottle?
There is capacitive detection, plates on the outside of the bottle...
What size and shape are these bottles?
Weigh it. Or at least put it on a plate with a spring that can be adjusted so you can tell full vs empty.
They're all plastic, semi- or fully transparent:
But again, from what I'm reading here Gravity: Non-contact Capacitive Flexible Liquid Level Sensor(5V)-DFRobot, it seems exactly like the thing to use. I simply don't know if it works only with water or not?
From the wiki:
Working Principle: The intelligent liquid level sensor uses the sensing capacitance of water to detect the presence of liquid. When there is no liquid approaching the sensor, the sensor has a certain static capacitance due to the distributed capacitance. When the liquid level slowly rises close to the inductor, the parasitic capacitance of the liquid will be coupled to the static capacitor, causing the final capacitance of the inductor to become larger. The changed capacitance signal is then input to the control IC for signal conversion, which will change. The capacitance is converted into the amount of change of an electrical signal, and then a certain algorithm detects and judges the degree of the change. When the amount of change exceeds a certain threshold, the liquid level is considered to reach the sensing point.
Would this not work with liquid soap?
What is the conductivity of liquid soap?
According to Google: the viscosity of the soaps should lie within the range from 1,000 - 3,500 cps (centipoises). The viscosity of normal commercially available cream soaps and liquid soaps lies in this range.
Why? I don't have the specific soaps being used in the dispenser at hand right now.
Conductivity, not viscosity.
I think you can be 99.99% sure it will work. Capacitive sensors should work with almost any liquid that is at least slightly conductive, so anything with water in it. Is the soap water based?
Ehhhh... My bad 
Well it would seem it does: Several liquids can be checked for electrical conductivity in the same way. We find that liquids like lemon juice, liquid soap, rain water, salt solution, etc. conduct electricity, whereas liquids like distilled water, oil, alcohol, etc. do not conduct electricity.Aug 23, 2020
I'll try at least. Thanks!
A piezo sensor/element attached to the wall would work. The resonance of the element would change drastically when there is soap behind it (vs air).
I do see a problem however. I'll guess the containers are HDPE. There are not a lot of methods to bond something to HDPE. I 'd not sure if a piezo element pressed against the container is enough to sense the soap.
Note, this suggestion IS NOT a distance sensor. It would be a single point sensor where the two outputs will be:
- soap is above the sensor
- soap is below the sensor
I would not expect a very precise sense point due to the soap being slowly lowered below the sensor.
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.