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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universam1 wrote 6 days ago point

I dont understand your goals, but theoretically why not!

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Richard Hogben wrote 6 days ago 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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universam1 wrote 5 days ago 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 5 days ago 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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Richard Hogben wrote 7 days ago point

Can this be calibrated for sea water specific gravity?

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