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 Home Brew Forums > Can it even be done? Measuring Specific Gravity using Arduino or Raspberry Pi
01-28-2013, 07:19 PM   #1
remthewanderer
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 Can it even be done? Measuring Specific Gravity using Arduino or Raspberry Pi

So. I want to track my fermentations a little better. I have brewpi installed on one of my raspberry pis. I know that this can track my temps just fine and it can integrate with arduino boards.

The holy grail for me would be the ability to see my specific gravity as it drops to get a ROUGH idea of whether or not fermentation is complete. I say rough idea because I just want a visual way to tell if a batch is ready to keg, I don't need to know if it finished at 1.010 or 1.015. This would be a nice to have feature but not necessary.

I've racked my brain and the best general solution I have come up with is to measure the capacitance of the wort and then use some math to translate that into SG. I've seen some charts on a salt water aquarium forum that did this math so I think capacitance measurements can correlate to SG.

But how to actually take capacitance measurements? I figure a food safe probe of some sort submerged in the wort. Pre-made EC probes are REALLY expensive. Enter the Arduino and the Capsense library.

Here is the hurdle for me right now: I don't currently own an arduino board.. I know that the cap sense library is used for touch based sensors and that people have used simple, food safe metals (could I use some stainless wire?) as the leads for home made EC probes. I have to assume that the capsense lib will output an integer or decimal value based on capacitance reading from the probe. I'm not 100% sure but I think the capacitance of wort will drop as the sugars change to alcohol. Can someone shed light on this? From this number I could work the math to get an SG or at the very least graph the number to see when it levels out.

Has anyone done anything similar? I've seen the beerbug kickstarter project which claims to measure SG but I have never read how they do it.

PS: How do large breweries know when their fermentation is complete? Do they take hydrometer readings manually or do they know that recipe X takes Y days to ferment out completely.

Can anyone here help shed some more light on how to digitally measure SG? I will gladly give you 1,000 internet points!

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01-28-2013, 08:44 PM   #2
crane
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I had a professor in college tell me about how she worked on a project for Budweiser where they counted bubbles to get an idea of fermentation activity. I did a similar thing on a smaller scale using an optical trigger on an air lock to count bubbles. It works great to get an idea of fermentation activity when you graph the number of bubbles per time period. I like this way because you don't have to stick anything in the beer therefore it doesn't need to be waterproof and sanitized. Also the output is a digital signal that you can easily read in and manipulate. If you go this route make sure you don't get an optical trigger that uses the IR frequency range as it will pass through the water just fine so it never triggers on bubble edges.

I did run into some issues when you have very rapid bubbles flowing out where it wasn't able to capture all of the bubbles. But I wasn't interested in that data anyway. I just wanted to see when it was starting to slow down to know when to rack it to the secondary without having to open up my fermentation chamber everyday

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01-28-2013, 09:05 PM   #3
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I am way too lazy to look it up but I've heard of highly sensitive scales being used and calculating various fermentation specifics based on lost weight.

... might be an easily obtainable and configured set up if I'm not on crack and dreaming the whole thing up.

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01-28-2013, 09:42 PM   #4
ryane
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I may be wrong but I believe for the aquarium salinity they are using Electrical Conductivity (EC) probes, not capactiance. EC probes are essentially measuring the ions in solution, so they wouldnt work measuring SG

Ive seen capacitance used for liquid level measurement, but nothing about gravity measurement. They do have digital refractometers though, you just put in a small sample valve in your fermentor and measure it that way, although Im sure you could modify them to your needs

IMHO though I feel like this is overkill, wait a couple weeks and call it good, in my experience with brewing, a little extra time rarely hurts, but rushing usually does

01-28-2013, 09:49 PM   #5
remthewanderer
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@crane - Thanks for the bubble counting example. I have heard of this done and I need to look into it further.

@Capebrewing - I've seen this too. I could use a set of sensitve load sensors to weigh the wort. I was not a fan of this method based on how I want to set up my fermentation chamber.

@ryane - We crap, I just assumed that EC was electrical capacitance not conductivity. RE: overkill. Absolutely this is overkill. It is more about coming up with a brand new way to use an Arduino or some other electronics to make this happen. The fun is in the build, not in the practically of it all.

I still need to know how the beerbug guys were able to do this. I think they will be at the AHA conference this year. I will have to ask them then.

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01-29-2013, 12:18 AM   #6
chip82
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As someone who works in a brewery, and my gf works at another. We still test gravity manually, not with a hydrometer but a device by Anton parr. We track daily what our gravities are till they are where we want them.

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01-29-2013, 12:28 AM   #7
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Wouldn't a neutral weight float on a linear encoder work best? It would be acting on exactly the same principle of a glass hydrometer, and linear encoders are immersion-proof and can be accurate to .00005" or tighter.

Or, alternatively, optical encoders, like those in a laser mouse. They have resolution high enough to measure .001" which is more than adequate. Solidly mount the laser above the liquid reading a floating scale.

Just throwing out some ideas.

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01-29-2013, 08:15 PM   #8
crane
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The problem I see with a float in a fermentor is:

1. Krausen drying out on top of the float and weighing it down.
2. CO2 bubbles sticking to the bottom of the float causing it to float higher.

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01-29-2013, 10:19 PM   #9
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The guys over at Brewpi are working on this, I think using some kind of tensiometer but I'm not sure. I don't know what hardware they are using but the beer bug team has a wifi/bluetooth enabled SG device in manufacture now. It also measures temp and calculates alc % And of course it can be monitored in real time remotely.

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01-30-2013, 05:15 PM   #10
remthewanderer
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@helibrewer: I am very familiar with the guy who runs brewpi. It is a bit annoying to me that he is not releasing details on his progress because he wants to try and patent something. This goes against my Open Source hardware ideals. I'm keeping tabs on him to see what he comes up with.

@Cathedral: Thanks for the ideas but I think that @crane brings up some good counter points. I'm still going to follow your path to a possible solution.

@chip82: So you take small samples off the tank to do your measurements?

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