Specific Gravity

I noticed that in earlier posts, you mentioned the development of a specific gravity sensor. I have a few questions regarding that!

Do you have an estimated date (it can be vague) that you might have it in production? Is it being designed for the new spark platform, or do you predict it being used in some other platform down the line? If it is made with compatibility with the spark, is there a chance it can work with older BrewPi units?

It will be designed to work with the Spark platform, but with the cheaper Spark Photon coming soon, I think I will put a Spark Photon inside, so it can be accessed as an independent WiFi device.

I put all my attention towards building HERMS parts in the last half year, but we have just continued or SG sensor prototyping. I expect it will at least take a few months before the next prototype is done.

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Okay, if a self-contained module that combines Brew Pi AND monitors SG at the same time becomes available, consider one sold! (And hopefully someone far more intelligent than I will modify it for existing Pi/Arduino users)

this seems to be a fairly simple project.
Two pressure sensors at different level in the fermentor. From the pressure differential SG can be calculated. You could run two tubes through the cap or pressure lock to different levels with the sensors outside the fermentor.

quick calc…0.5m liquid height…1.060 gravity = ~5000 Pa (5 kPa) drops to 1.015 gravity = ~4800 Pa (4.8 kPa)…ie. drop in pressure over 0.5 m of 200 Pa or 0.2 kPa.

Am I missing something???

I just ordered me first photon so I will work on it over the next month.


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In principle this will work. (I’ve long had plans - but no time - to add this to my boil kettle.)

I just wonder if there are practical concerns that make this difficult?

what practical concerns come to mind?
you can use a 2 ported differential sensor 0 to 5kPa which should be precise enough.

we plan to use this in 1.5bbl fermentors I could see the boil kettle being a more of a challenging environment .

problems I see are dissolving of the gas in the tubes over time and the wort moving up the tube. I suppose the system could be closed with a gas bladder or something. I don’t know of a submergible sensor.

ill keep you posted on progress or problems.


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I have been looking at sensors. Ideally one with a range of 0 - 1Kpa . The best I could find is a mpxv5004DP differential pressure sensor. This sensor has a 0-3.94 range which might be sensitive enough.

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I didn’t know it could be measured like that. It explains why SSbrewtech 20 gallon has the 2 tube to measure liquid height.

oh, I didn’t mention, I was going to use the brewtroller bubbler method so that dissolving gasses, or contraction/expansion of gas in the tube isn’t an issue.

I am not sure I understand why they would need two tubes for measuring kettle volume. I will look into it.

using differential pressure compressed gasses or the like shouldn’t be an issue. Fermentation bubbles as the rise may change the SG a bit during fermentation but as fermentation slows accuracy should return.

I have constructed a proof of concept sensor and am satisfied it will work.

I need resulution of 100 over a SG of .1 I think that is well within the ability of an arduino and a differential sensor.

question about photon.

I assume it is much like an arduino in that a voltage allied to an analog pin returns a number representative of the voltage. is it 1 - 1023? or 1 - 4000? like a Due?=

most of the sensors have an offset. 0 kPa return a voltage of .75 volts. Can the analog pin be set so .75 volts returns a 1 ?

thats all for now


can you describe the bubble method?

Hi there,

It’s described here:

never mind I found it on their site. interesting way to get around the problem of gas solubility in the tube. I would like to get aroount it with somesort of a diaphram as it would a waste of CO2 . Although I could pull CO2 off the blowoff tube ??? what do you think? interesting…


So using differential pressure has turned out to be harder than I thought. Using open pipes works as long as they are 1/2" or so. Using 1/4 produces inconsistent results probably due to capillary issues of the liquid in the tube. I tries a variety of bladders ( balloons, fingers of gloves, etc) none of which provided even close to satisfactory results.

So I am going to try a different method.

A weight of some sort suspended in the wort/beer should weigh differently depending on the specific gravity. I intend to attach it to a strain gauge/load cell kinda thing

That is how I am doing it in my prototype.

have you had any luck? Any thoughts?

Seems to me that if I use a load cell that is 0 to 100 grams and use a weight that is 75 grams with a SG of 2 g/cc then the change should be a few grams

I have my doubts that this would work in boiling wort - the churning of the wort will easily skew the measurement.

I’m going to use 2 bubblers - the pressure to displace the two columns of liquid are the same regardless of any turbulence in the liquid as it boils, or suspended solids, and since there’s no liquid in the tubes capilliary action isn’t a concern either.

let me know how it goes. I intend to use it in the fermentor.


I am so excited!! suspending a weight in the beer seems to work. I have a load cell attached to an arduino via an hx711 ADC. From the load cell I have a golf ball suspended into liquids. the golf ball has a SG of roughly 1.2 and a volume of roughly 45 grams. With this setup I am getting 140 points of separation between clear water and sugar water of 24 plato ~1.1 . The results are stable and repeatable.

I am thinking the weight needs to be something other than a golf ball with a volume of 75cc with a SG of maybe 2 or 3 Blown glass ball with weight inside to get to proper SG. Any ideas?

Question, the 711 requires 5v right? if I were to use a photon which is 3.3 volts how does this work I am told the pins are not tolerant of 5v.

thanks steve

I think this is what The Beer Bug does. I think there will be a problem when fermentation slows and CO2 starts to adhere to the float and make it lighter than it really is. You might be able to add a vibrator like what is used on a mobile phone to shake the float right before reading.