DIY electronic Hydrometer

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iSpindel measures specific gravity and temperature regularly. The inclination angle of the floating device changes in relation to the device’s buoyancy, and therefore in relation to the sugar content of the fermenting liquid thus measuring the fermentation.

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The system is based around the use of a heeling (or tilting) cylinder, an ingenious and easy concept - you do not need any external reference (except for gravity) and the cylinder is extremely easy to keep clean. The inclination angle changes in relation to the buoyancy and thus directly in relation to the sugar content. There is an angle formed between the center of mass and the center of buoyancy depending on the density of the fluid.

Therefore the idea is to place a Wifi-enable IoT device with an accelerometer and temperature sensor in a floating cylinder. The system will measure the sensors and every x-minutes it will connect to the Wifi and sends its tilt angle, temperature and battery voltage to a cloud service like to store the data.

With an update interval of 30min it was possible to achive a battery lifetime of almost 3 months!

Metacentric Height

Actually, this is the "metacentre", the cylinder will tilt as the liquid density changes in relation to its center of mass and center of bouyancy. The angle of tilt can then be measured.

It is possible to trim the cylinder by adding a few grams on the bottom so that the cylinder is more upright, or on the lid, so that it is more tilted.

The software calculates the Euler angle for X and Y from the XYZ acceleration values and forms the absolute angle. We compute these with the calibrated parameters to ° Plato, SG or similar by correlating to measured references.

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Tom Anderson wrote 04/09/2017 at 22:09 point

One of the challenges with using sensors in fermenting liquids is to avoid errors caused by bubbles clinging to the sensor. If you don't find an enclosure material that avoids this problem, perhaps you could add a small vibrator that would gently shake them off.

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TegwynTwmffat☠ wrote 04/29/2017 at 09:44 point

Yes and you've also got foam and bits of plant material eg hop leaf that will spoil the results. It's a great idea, but really fluid needs to be pumped from the main tank into a separate auxiliary tank, filtered and maybe de-gassed to get a useful result?

It would however be perfect for a distillery where no flotsam/gas is present.

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Raphael Collares Toselli wrote 05/09/2017 at 04:31 point

I think he has tried that, with no success.

The next step should be something like a hydrophobic food grade coating, or another container that does the trick... However i suspect that the goal of his project is more like an idea of the approximate SG rather than the exact pin point gravity readings. I'm really excited for this, as a data freak and homebrewer myself.

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rogerlewinton wrote 04/06/2017 at 19:28 point

I have the parts in front of me now building my own.

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rogerlewinton wrote 05/01/2017 at 07:42 point

Have finished the build at last. Life does get in the way. I have it sitting in the fridge connecting every 90secs to a wifi hub on other side of the house. That should test the battery life at low temps. See its performance here.

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Richard Hogben wrote 05/12/2017 at 21:36 point

Battery getting low!

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Krismith wrote 04/03/2017 at 11:53 point

wow superb work!! One of the best ideas that I have seen!! 

 Best of luck

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Ember Leona wrote 03/31/2017 at 22:42 point

hows it work? is it lighter because the water pushes it up? How does it work in soil?

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breezecar wrote 03/30/2017 at 12:14 point

What type of battery is used in this project?

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Legrange wrote 04/13/2017 at 14:22 point

First battery is a Panasonic NCR18650B, next one is an unknown 18650 sized secondary lithium.

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Samuel Lang wrote 03/21/2017 at 13:00 point

I dont understand your goals, but theoretically why not!

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Richard Hogben wrote 03/21/2017 at 17:25 point

To track the changes in temperature and salinity in a saltwater aquarium. Current options are more expensive probes and controllers, etc. 

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Samuel Lang wrote 03/22/2017 at 14:34 point

Do you know how much the density will change? Therefore we could compare it with known density changes by sugar in the wort.

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Richard Hogben wrote 03/22/2017 at 17:20 point

Hydrometers sold for aquariums usually test between 1.022 and 1.028 specific gravity. Depending on the volume of saltwater and evaporation rate the SG can fluctuate +/- 0.03 weekly if not automatically replaced with fresh water. The goal is stability, not an exact value.

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Samuel Lang wrote 03/29/2017 at 20:19 point

I could imagine that life activity in your aquarium or medium flow might be the issue to have a static position of the iSpindel, but I haven't tested it.

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Richard Hogben wrote 03/29/2017 at 21:26 point

This would be placed in the sump area where there are very low flow areas. For example where a float switch for auto top off would be placed. It sounds like I can definitely give this a try, thanks!

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Richard Hogben wrote 03/20/2017 at 22:37 point

Can this be calibrated for sea water specific gravity?

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