I know this dead horse has been poked far to many times. But I'm about to embark on an extremely complicated build, I'm making an advanced customizable personal vapovizer (ecig for ejuice only). I want to integrate a fluid level indicator, but my tank will only be about 10ml in capacity, so very small. I'm leaning towards a capacitive sensor wrapped around the rubber feed tube. Any suggestions?
10 mls :.
Maybe use a syringe and drive it with a stepping motor.
The number of steps moved would give you an indication of fluid used.
Above is what I'm building in its most basic form, the fluid is drawn through inhalation or osmosis. If it's forced it could over saturate the atomizer coil & short out the device. I'm just looking to detect how much fluid is left, so it can be displayed. Hoping for decent accuracy on such a small scale. I'm thinking a capacitive system, or resistive, with an amplifier circuit to increase accuracy.
Capacitive on the feed tube or resistive probes in the chamber should work if the fluid is electrically conductive. What exactly is the chemical composition of the fluid to be sensed?
The composition is fairly simple, with minimal ingredients.
- Water
- Alcohol
- Propylene glycol (PG)
- Vegetable glycerin (VG)
- Nicotine
- Food grade flavoring
- Food grade essential oils
Water or alcohol is used to dilute the juice.
The PG can be used in conjunction with VG, or just one or the other.
Nicotine, flavoring, & essential oils are optional.
It's not looking good. I'm no chemist, but most of that stuff doesn't appear to be conductive at all.
Tap water is conductive enough to detect due to impurities like magnesium, but pure water is an insulator. Do you know which kind is used, and if it's tap, what percentage of the solution is water?
Propylene glycol conducts slightly, but again, it's only a part of the overall solution, so probably very difficult to detect. Same goes for essential oils -- only some are conductive, and even then only slightly.
I'm making wild guesses here, but I suspect that electrical detection is going to be difficult. It may be worth grabbing an op-amp for a quick test, but beyond that, I'm not hopeful. And anything you add the liquid to make it conductive is probably going to damage your atomizer.
So, throwing out wild ideas here -- how about putting a little plastic float in your fluid chamber, with a little chunk of aluminum or a tiny rare earth magnet attached to it. You may be able to capacitively sense the position of the metal/magnet from outside the container.
Another idea is to put a pressure sensor on the bottom of your fluid chamber and measure the weight of the liquid pressing on it. 10ml probably isn't going to be heavy enough to be easily detectable, though. You may need a balance beam (like on an old-school weight scale) to "amplify" the weight applied to the sensor. Or use the balance beam but sense the position of the far end of the beam rather than the weight on it.