This is part four of a series on monitoring homebrew fermentation. In parts one, two, and three, I experimented with data I downloaded from one platform and uploaded to another. In this part, I create some new sensors to try.
I have hardware!
And it’s pretty slick. Using any I2C device with Helium’s wrappers is some of the easiest hardware hacking I’ve ever done. This is my first time using Lua, but while it made some different choices than other common languages, it has been very easy to learn.
Maybe an example will prove my point. This is how you take a reading from an ADXL345 accelerometer (
he is Helium’s built-in library):
|addr = 0x53 — Default I2C address|
|reg_pwr_ctl = 0x2D — Power control register|
|pwr_ctl_on = 0x08 — Active measurement mode|
|reg_x0 = 0x32 — X0 register|
|length = 6 — Bytes for a full measurement|
|— Power up|
|— ADXL345 starts in an idle mode; activate it|
|he.i2c.txn(he.i2c.tx(addr, reg_pwr_ctl, pwr_ctl_on))|
|— ADXL345 automatically advances through the rest of the|
|— axis registers, so we can read them all with one command|
|status, buffer = he.i2c.txn(he.i2c.tx(addr, reg_x0),|
|— values are 16bit, little endian, signed integers|
|if status and #buffer == length then|
|x,y,z = string.unpack("i2i2i2", buffer)|
While building such a script, you can fill it with
When you’ve acquired the measurements you want to save, you send them to Helium’s cloud platform like this:
|now = he.now() — time that we took the reading|
|— "f" is "floating point type|
|— port, time, type, value|
|he.send("x", now, "f", x)|
|he.send("y", now, "f", y)|
|he.send("z", now, "f", z)|
Once you have posted data, you can use Helium’s dashboard to check it out:
This system is so smooth that in just a week (of evenings) I’ve been able to write scripts to take readings from two different sensors. Those sensors are now sitting in the bottoms of two carboys monitoring the fermentation of an English Mild. Yes, the first thing I did with my new electronics was submerge them in infected sugar water. I tested the water tightness of their containers … oh, at least several times.
What monitoring a fermentation amounts to is measuring the density of the liquid. Water with sugar in it is denser than water on its own, or water with alcohol in it. As the yeast convert the sugar to alcohol, the liquid becomes less dense.
Most tools test the density of the liquid indirectly, by instead testing the buoyancy of a known float. The standard hydrometer is a float with a scale attached, so you can read how high it’s floating by looking at it.
The device I’m looking to replace, the BeerBug, reads this float-height by suspending the float from a flexible metal tongue, which is also connected to a magnet, whose position is read by a hall-effect sensor. As the float floats higher, the magnet nears the sensor, producing a stronger reading. It requires that you measure the gravity of your liquid with a hydrometer first, but once the initial reading is calibrated, the change in buoyancy can be measured (the magnet moves farther from the sensor as the beer ferments).
I wasn’t able to obtain a hall-effect sensor as quickly as I wanted, so my devices take different approaches. The first is based on someone else’s design. By making the float very buoyant on one end, and just barely not able to float on pure water on the other, the angle at which the float floats will change with the density of the liquid. So the float should start close to horizontal when the unfermented beer is very sugary, and end up more steeply tilted as the sugar is converted to alcohol. The sensor in this float is thus the ADXL345 accelerometer that the above code demonstrates using. By measuring the direction of the force of gravity, we can figure out what angle the sensor is floating at.
The idea behind the second experimental sensor is to directly measure the increased pressure from the denser liquid, instead of measuring its effect on buoyancy. I’ve place an atmospheric presure sensor in a non-rigid housing, which should allow the liquid to squeeze the air around the sensor, raising the pressure around it. As the liquid becomes less dense, the pressure should reduce. The sensor has been placed at the bottom of the carboy, to get as much liquid above it to provide pressure as possible. I’m also taking readings from the pressure sensor on the Atom, which is sitting in the open air outside the carboy, so I can compensate for weather-related pressure changes.
So far, I’m just collecting raw data: pressure readings in the latter case, and force readings in the former. It’s going to take some analysis to figure out what they mean. Unfortunately, the BeerBug site is currently only serving the most recent reading, and not history, so direct comparison of data will not be possible for now. The Helium site is running smoothly, though – and in addition to their dashboard, as shown above, I can also use the graphing code from my earlier experiments:
I’ve shared the code I’m using for these experiments on Github. Please feel free to download and use the code yourself, or to suggest ways I can improve my Lua! Check back soon for analysis of how the measurement and fermentation went.
Update: the first bit of analysis, from the temperature sensors is up in part five.