Microcontroller | The DIY Brewery

So, in my last couple of posts I was doing some research around coming up with the perfect Electric Counter-Top Brewing System. I found what I thought would be a perfect Mini-Brew-in-a-Bag Electric System with the Cajun Injector Electric Fryer, however the Temperature Controller that comes with it could not maintain the temperature accuracy nor the range needed to brew the variety of beers I wanted to make.

So as any industrious DIYer would do, I took apart the Temperature Controller to see if I could modify it. There are six screws in the back of the unit along with two under the face plate that hold the housing together, once removed the housing can be snapped apart to get to the components inside.

As you can see in the diagram, there are several components that can be reused to drive the heating element from an external controller, all I needed to do is figure out what connects to what and build out a schematic that I can use to build a controller interface that I can drive with a Microcontroller.

The Safety Switch acts as a master switch for the incoming power, If the unit is not seated in the Cajun Injector slots for it, no power will flow to the unit. Now this is a pretty nice feature that cuts power to the heating element should you pull it out of the pot and set it to the side. You also don’t have to worry about dry firing the unit if it is not seated in the pot. However, you still have the dry fire issue when the unit is properly seated in the pot.

The Unit also contains what looks to be a GFCI Breaker that is wired to a probe that runs along side the heating element.

There is also a 12VDC Relay that controls turning the heating element on and off based on the control signal from the control panel.

Finally to power the control panel there is what looks like a reduction transformer that should provide the 12V power needed to drive the relay.

The control panel has an LCD mounted on it and what looks like a microcontroller or Programmable Logic Array which is the brains of the Temperature Controller. From a quick inspection it really doesn’t look like it contains anything of use.

There were three connections from the control panel to the components in the housing. These look to be an input voltage, the Thermistor input connections and the Relay control outputs. I should be able to extend these to an external controller and drive the heating element.

I also performed a little research by hooking up the Thermistor to my Multi-meter and measured the resistance at several temperatures. What I got was a pretty broad range of resistance; 3.58 M ohms at 40 degrees F down to 80 K ohms at a rolling boil. Now without knowing the actual part number of the Thermistor I really didn’t think I could come up with a temperature curve that I could use to figure out the temperature based on the resistance. Luckily after a little searching on the Internets I came up with a program that would generate a set of temperature coefficients based on a couple of readings at known temperatures. With this, I plan on reverse engineering the temperature coefficients of the Thermistor so I can come up with a resistance curve that I can use to determine the temperature by using the Thermistor in a voltage divider and then calculating the temperature value based on a known voltage.

So my next steps are to do a little more poking around the components and determine the transformer’s output voltage is and start coming up with a plan to build out a controller board that I can use with a Netduino to drive the unit.

So stay sanitized and keep an eye on those fermentation temps and I’ll catch you for a pint around the keg.

Jim Lavin – Otaku Brewer

One of the most important things in brewing beer is temperature control. Matter of fact, one of my fellow club members is very fond of saying, “Come back and talk to me about brewing great beer after you have temperature control in place, because If you don’t have temperature control, there is no way you can brew great beer.” And I have to agree he is right, temperature control plays an important part of the entire brewing process. Not only do you need temperature control during the mashing process, you also need it during the fermentation, lagering and storage processes.

As part of building my Electric Brew System I’m going to need to control the temperature of my mash and I want to be able to program a mash profile and let the system notify me of significant steps in the process. To manage temperature you have to monitor it, so I started out building my controller with baby steps.

First I wrote the simple things like the control interface and services and then I broke the various parts of the automation control into separate circuits that could be built and tested by themselves.

I started off with the temperature monitoring circuit. What I wanted to be able to do, was set the interval that the microcontroller would read the temperature sensor and then log that to a file on a SD Card that I could then use to display a graph of the temperature over time. The DIY Brewery Temperature Logger project is the result of that first phase of development. It is a Netduino Plus Project that provides a web-based temperature monitor.

This project has several parts:

CodingSmackdown.ControlInterface – A jQuery based website that is hosted on the Netduino Plus’ SD Card and served using the NeonMika.NETMF.Webserver. It provides a self updating view of the temperature history as well as a settings tab that allows you to change the logger’s settings as well as the Netduino’s Network settings.

CodingSmackdown.Services – A C# .NETMF Library that contains the various threading libraries to handle the NETBIOS Name Resolution, NTP Time Client and Temperature Logging. It also includes classes to handle accessing the various GPIO and Analog pins on the Netduino and other various base and support classes used by the project.

CodingSmackdown.TemperatureMonitor – A C# .NETMF Application that is responsible for loading up the various services at start time and provides classes that are used by the NeonMika.NETMF.Webserver to process jQuery requests sent by the web client.

JSONLib – A C# .NETMF Library used to format the various responses in JSON format for use by the web client. The original code was written by Wouter Huysentruit and can be found over at http://code.tinyclr.com

NeonMika.NETMF.Webserver – A C# .NETMF Library that provides the entire web server for the project. The original code was taken from the NeonMika.NETMF.Webserver project here on codeplex over at http://neonmikawebserver.codeplex.com This version was paired down specifically for this project and to meet the memory constraints of the Netduino platform. For the latest version please reference the original project.

Below are pictures of the user interface and schematics of the temperature sensor circuit, so you can build it yourself.

The main page retrieved by navigating to http://netduinoplus/index.html

The Settings Tab that can be used to change the Temperature Logger’s behavior and network settings

The breadboard layout of the temperature sensor circuit

The schematic of the temperature sensor circuit

Images of the prototype Netduino Shield that holds the temperature sensor circuitry

You can find the source code and updates to the project at http://diybrewerytemplogger.codeplex.com/

Till next time, stay sanitized and keep an eye on those fermentation temps and I’ll catch you for a pint around the keg.

Jim Lavin – Otaku Brewer

The DIY Brewery

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Tag Archives: Microcontroller

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