# Digitial Hydrometer Sensor

### Help Support Homebrew Talk:

#### russellqwerty

##### Member
Task: Create a digital sensor for an arduino or similiar microprocessor that can measure ABV, with a price range of under \$50

Umm... okay?

OP

#### russellqwerty

##### Member
I only have a software background, so implementing a single sensor is like a mystery to me.

I have been researching ways to use a couple of different existing sensors that could be used to determine the abv.
-Find a way to calculate a Density reading, mass of the solution,divided by the volume of solution

Calculate Mass Change

-A way to measure the CO2 coming out of the carboy using a blowoff tube, collect the expelled CO2 and use a pressure sensor to measure the amount given off
-Need a way to measure the mass of the trub
-Subtract the mass of the trub and the mass of CO2 from the original mass

Calculate Volume Change

-Using the mass of trub you should be able to do a couple of conversations to calculate the new volume of the system​

-A SG reading is just the density of the beer divided by the density of a known solution (water) at that given temperature

-Another idea I had was to use a colorimeter which can be calibrated with the wort and water
-Measuring the absorbance of UV during the course of a fermentation and during a clearing period
-but you want to avoid UV radiation as to not skunk your beer, so..​
I am also thinking of other ways, but I am trying to keep this cost effective. A single sensor would be preferred but if it could be done with a collection of sensors for a modest price I would be open for that as well

The ultimate goal here is to be able to monitor the ABV and temp during the course of a fermentation, and possibly send a text/email, or have a simple webpage that can give updates, and help monitor the fermentation.

And yes, I do know about the ferMonitor but that does not seem to be available currently

#### theonetrueruss

##### Senior Member
Maybe a motion sensor that calculates velocity of sinking? Theoretically a more viscous fluid should cause slower sinking. Maybe the sensor would be a cylinder with the actual sensor in it and the reading would start when the cylinder hits the bottom of the test sample and releases the sensor. Then the reading could be done consistently.

No idea how to do that. just thinking. Intriguing question. I bet something involving refraction would be easier.

#### audger

##### Well-Known Member
all while being sanitary and waterproof...

well if you wanted to digitize the mechanical hydrometer, all you would have to do is put a hollow (and buoyant) air-filled bead or cylinder of known volume and attach it to the end of a shaft. the other end of the shaft is a pressure sensor. let the hollow bead hang from the sensor and calibrate it to gravity. then calibrate it to 100% water. from those numbers you can then correlate how much buoyancy the bead has in a given beer and calculate the ABV.

or- you just take the FG minus the OG and multiply that number by 131 = ABV

#### LordUlrich

##### Well-Known Member
using a scale like this

and a weight, i was looking at copper tube (boil kettle not for fermenter), although stainless would work, build a weight with a bulk SG of 1.90, i was planning about 6 in of 1 inch pipe, with a cap on each end (sealed air/water tight).

suspend the weight from a thin cable of some type, and use the change in apparent weight (ie the buoyant force) to calculate the SG of the fulid.

Somebody should check my math on size of the weight, but my calcs said it would yield an accuracy of 0.01 SG

OP

#### russellqwerty

##### Member
Thats more of a manual way to do it. How would the board be able to read the scale? I like the idea of using buoyancy and a pressure sensor. If you use a refractor is the amount of UV radiation small enough not to alter the flavor of the beer?

#### LordUlrich

##### Well-Known Member
I was going to strip grab the wires off the strain gauge hook them into a instroment amplifier. Plain strain gauges are expensive, electronic scales are a cheap source of strain gauges...much like the spa pannel vs gfic breaker delema.

#### StMarcos

##### Well-Known Member
Laser light through a prism, diodes sense the refraction. Pass small amounts of beer through a filter and then through a channel on the front of the prism. ?

#### dozer4412

##### Well-Known Member
I think coderage is working on making one of these. Some of us have been waiting and watching for one of these to actually come on the market. Maybe we'll get lucky and coderage will post something.

I'm in the same boat as you, my background is in software and not EE and making one of these sensors myself is more than I am willing to bite off. I'd love to purchase a sensor like this and would be willing to pay a good deal more than \$50 for one with even ok accuracy.

#### Farside

##### Well-Known Member
I'm looking at implementing this with two tubes in parallel.

The first (thin) tube has a level sensor attached (https://www.alliedelec.com/Images/Products/Datasheets/BM/OPTEK/387-0043.PDF) and is used to set the liquid level to the "zero" position.

The second tube is larger and has an IR distance measuring sensor at the top (http://sharp-world.com/products/device/lineup/data/pdf/datasheet/gp2y0a21yk_e.pdf) which measures the air gap between it and the top of a weighted float that sits inside the tube.

The higher the SG, the shorter the distance.

The distance sensor is about \$10: http://www.robotshop.com/ca/sharp-gp2y0a21yk0f-ir-range-sensor.html
The level sensor is about \$5: https://www.alliedelec.com/search/productdetail.aspx?SKU=3870044

All up, one could probably put something together for under \$50

#### audger

##### Well-Known Member
unfortunately that distance sensor is no where near accurate enough. depending on the finished configuration (mainly, the float used), you are probably going to need to measure to +/- 2mm, if not tighter. you would realisticly want a laser range finder (and sutable target float), or a float linked to a linear encoder.

when you are doing it optically, you also then get into how to ensure the liquid or steam present doesnt interfere with the measurement, interfere with the mechanism or movement of any floats, temperature compensation, etc.

#### Farside

##### Well-Known Member
I put an excel spreadsheet together to test what sort of weight for a given volume of liquid I should expect allowing for temperature.

I got some emperical data from the web for the variation of density of water as temperature changes and found two formulas that closely approximate the emperical data:
http://www.flickr.com/photos/[email protected]/6240302671/in/photostream

Hope this helps.