In my last automation post I talked about some new sensors I had purchased for use with my arduino board. They arrive and I have had a chance to play with them all, so I thought I would describe the results.

Thermistor Probes

The thermistor probes I purchased were straight Ranco ETC replacement probes. I've had good success with these ETC's and they were relatively cheap, so it was worth a shot. The thermistors themselves seem to have a resistance on the order of 650-700 K ohms which is much higher than the 2.2Kohm probes from the love controllers. As you can see from the profile on the right, the temperature to resistance calculations are fairly linear when the temperature is above 30 degrees F.

To test the probes I took four samples:

1. In a cup of ice: 32.7°F
2. Room temp water: 72.8° F
3. Hot tap water:  109° F
4. Just boiled water: 178° F

For each sample I took a resistance reading using my Ohm meter and checked the corresponding Analog to Digital value (0-1023) from the arduino board. For all samples a used a 10K ohm resistor in the circuit. Results are in the below table. Essentially what I found that between the change of 145.2° F I saw a total change of 669 digital. That's approximately 4.6 digits per degree, or 1/4 degree resolution. These probes should be more than sufficient.

Raw Ohms	A2D	Temp
998	931	32.7°F
29.52	764	78.2°F
13	586	109°F
3.4	262	178°F

Ultrasonic Range Finder

The range finder is essentially sends out sound waves in a very narrow beam and detects how long it takes for a return ping. This allows you to tell how far away something is from the range finder. My plan is to use this for boil over prevention and maybe even tank level detection.

I played with these a bit and they definitely can detect an object fairly easily. There seemed to be a bit of noise, but I am writing most of this off to it not being held in a fixed position. The documentation proclaims that the device will change the analog voltage 10 millivolts per inch, and my tests show this holds well. The one downside is that anything 6 inches or closer always gets reported as 6 inches, so I will need to make sure the device is at least 6 inches above the level I want to detect.

One other potential downside is moisture and temperature. The documentation also states that changes in temperature can effect performance because the device will do calibration upon power up and any changes in temperature will effect the results. This may mean I need to reset the device every 10 degrees or something, which is promoted as an option in their documentation. I also, don't know what the moisture from steam will have on the device. My guess is it probably will break it, which doesn't help much...

 

Accelerometer

The goal with the accelerometer was to detect vibration from the airlock as a means for determining fermentation progress. To do this I bought a +/- 1.2g accelerometer and board that outputs X and Y values to analog. I soldered this one up yesterday and finished the testing today, with some interesting results.

What I found is that in a static environment the device will only deviate 1 point in either direction (+ or -) from a midpoint. This can be observed from figure 1, which shows a program I wrote to visualize the X and Y values across time.

Next I moved a computer into the laundry room to try and get some samples from an actual fermentation. Initially I found way too much noise coming from the device. I eventually isolated this to the USB cable of all things. For some reason the other USB cables I had must have been poorly shielded and were somehow making the A2D readings vary greatly. You can see what I mean from figure 2, which the only difference from figure 1 is the USB cable used.

Lastly, I moved the mead bucket into the main room, to test with the working short USB cable. What I found is generally the accelerometer did a good job. It detected most of the bubbles but not all. Maybe I need something more sensitive or maybe I can get most of the data out with some pattern analysis. I did find the raw sampling to be a bit noisy. You can observe this is figure 3. It shows obvious blips where bubbles occur, but detection is hard with all the +/- 1 noise. To clean this up a bit, I changed the program to only draw lines that had a change of 2 or more from the midpoint. This helped a lot as you can see from figure 4.

Next I think I will try sampling a little faster (currently about 9 times per second) to see if I am missing some bubbles due to the slow sampling, and work on some pattern analysis that gives me the best detection pattern.

I started thinking about temperature logging again because I remembered the Ranco ETC's have an optional analog 10V output of the temperature. While my Ranco controllers don't have this option, it occurred to me that maybe I could use my Arduino board to test some temperature logging.

My first thought was to try it with my existing temperature probes from the love controllers I have in my control panel, with the fermentor to get a nice fermentation graph over time. I have played around a bit with the probes and was able to get them to change resistance as temperature changed. I took a lot of trial and error to find the right circuit and still am not sure about what resistor is right for the dividing. Essentially what I am seeing for these probes is a 805 Ohm resistance around 30 °F and a 1.5 Kohm resistance around 175 °F. The resistance pattern seems to indicate that the probes are 2.2Kohm thermistors (manual doesn't say), which would indicate a 1K-2.2K resistor would work great. Unfortunately I don't seem to get the resolution I want. Somewhere around .5-1 point on the A2D per degree fahrenheit. Not sure if the problem is the board, A2D chip, or probe, but that resolution is a little less than desirable.

To help solve the problem I bought another board and a 10K thermistor that others have used with the board. This should help me diagnose the problem. I also went ahead and purchased two replacement sensors for the Ranco ETC's I have to use with the board. They are also 10K so should have a similar circuit and behavior. I'll provide an update when I see how these all work.

In addition to the temperature purchases I also got two more sensors to play with for other potential uses. The first is a accelerometer. My intent is to use the dynamic function of this device to detect vibration. Vibration of what, though? The idea would be to attach the sensor to the air lock on a fermentor and record the bubble rate over time based on the amount of vibration. It's just an idea, but it would be a cool way to record and monitor the progress of a fermentation when not at home.

The second new sensor with potential is a ultrasonic range finder. This is a simple device that detects how close it is to things and provides analog feedback. My initial thought was that this would be perfect as a boil over prevention mechanism. The idea being that the gas could be shut-off by triggering a solenoid when the range finder detects the liquid getting too close to the top. This would be pretty cool if it worked. Then I began to think that if this worked well enough it could also be used to detect the level of liquid in the HLT, Mash, or Boil. This would prevent the need for float switches to prevent overflow, detect levels, and even determine how much liquid has been transferred between kettles.

The last automation piece I am still working toward but is further out on my list, is a liquid propane regulation controler. Currently the methods for regulating gas would be to use a solenoid device that either turns the gas on or off. This works, but doesn't allow for fine grain control and heat maintenance. My idea is to use a stepper motor attached to a variable high pressure regulator. This would allow the computer to adjust the gas output on the burner depending on the situation by automatically turning the regulator nob using the stepper motor. Haven't done too much with this yet, just have the motor and stepper control board. Though I just put in an order for the connector that should help me wire the two together for testing.

Fresh off of another good brew, I decided it was time to begin work on the control panel and components again. I had just received a few components from McMaster-Carr that enabled me to move forward with tank holes for the new additions. To start I decided to test and prepare for the auto water fill and shutoff for the HLT.

Parts

The parts that I received that enable me to do this include the following:

• 1/2" Stainless Plugs: in case I need to seal off any holes without the intended device in place
• High Temp O-rings: used on both sides of the tank to seal the hole
• 1/2" Stainless Lock-Nuts: tightening over the thread inserted into hole in tank

Assembly

First step: was drilling the hole into the side of the tank. This consisted of finding the high part on the tank side with no curve and drilling a 7/8" hole. This is relatively easy with a metal hole saw, assuming you go real slow.

Second step: was inserting the float switch, aligning it correctly (normally closed), and sealing it off by using two O-Rings and a lock-nut on the inside. The outside of the float switch also has a 1/2" thread which will be helpful. My intent is to permanently affix a coupler to the back half of the float switch thread, connect the leads to a female port that sits inside the coupler and affix the inside coupler with glue. This will enable me to remove the leads for cleaning.

I continued by affixing the wires from the float switch to the back of the control panel at the appropriate spots.

Third step: was connecting one side of the solenoid to the hose and the other to the HLT tank. The solenoid is normally closed, but interestingly some water did get through until full water pressure was applied from the hose. I then connected the solenoid to the appropriate ports on the back of the control panel

The test: so the idea behind this whole thing is to have push button water flow, in addition to auto water shutoff for the HLT. If you look at the control panel you will see a push button at the top. This is a momentary button and is used to open or close the solenoid. What is happening is the button is connected to a triggered relay that toggles its state on or off when it is pulsed. Thus, every time I press the button the relay gets pulse and 24 volts are sent to the solenoid to open it. When the button is pressed again the relay is triggered closed, cutting of power to the solenoid, thus closing it. The float switch works the same way essentially. When the float piece is down and the tank is low the connection in the circuit is closed, but when the water raises the floating piece level the connection is made. Thus, when the button is pressed the first time the HLT will start filling, but once the float switch circuit opens it will trigger the relay to close. The result is of course that the water stops flowing.