One of the common challenges to craft-brewers in the home is regulating temperatures for mashing, fermenting, lagering and serving. This project shows you how to build a simple, versatile and reliable unit capable of controlling fridges, kettle elements, light bulbs, and even cooling fans.
Version I used analog electronics to switch a relay with mains voltage (240VAC) on the contacts.
Version II uses new technology which makes it easier to build and use. It is controlled by a picaxe microcontroller, and is more versatile because it uses solid state switching.
The capacities
of the controller are many and great because it can be programmed.
It can
easily do all of the following things, and more ...
At the heart of the temperature controller is a picaxe 08M microcontroller.
The PICAXE reads a temperature from a Dallas DS18B20 digital probe. These devices are cheap, accurate, and easy to calibrate. They also make programming a breeze.
The ‘live’ switching is done using solid state electronics. The unit uses a zero-crossing detector, meaning the AC switches when it passes through zero volts, reducing stress on components. We can do things like vary the power output of a mash heating element by switching the element on and off many times a second (much like a light dimmer works).
The unit also has inbuilt capacity to switch a DC fan. This means it can operate a Son of a Fermentation Chiller. If your fridge has passed it’s used-by date, you can still use it as a cool box by supplying your own ice and using this control unit.
The programmable chip means the controller is extremely versatile. You can change it from heating mode to cooling mode just with the change of a keystroke. If you require cooling in the summer or heating in the winter, both are achieved very simply.
The picaxe controllers are versatile and easy to interface to a wide variety of input and output devices. Check out the picaxe web sites for more details. This means there are many possible ways to build or implement a unit like this. This project presents one method, your own requirements might lead you down a different path.
The unit uses a couple of pushbutton switches to alter the set temperature (up & down). You could use a variable resistor (potentiometer) to do the same thing, or even leave them out - just pre-program your set point and fix it at that.
A temperature probe of some kind is essential, and the Dallas digital probe interfaces simply with the picaxe, providing an accurate digital readout in degrees Celcius.
I’ve made several of these units, to control different fridges. My first controller used a 16 character by 2 line LCD display (AXE 033) to show actual and target temperatures. I’ve made a second unit without the LCD to save costs (LCD units are around $A45 each). The second unit controls my serving fridge and I have no need to change the set point on that one. Rather than using an LCD, it would be simple to use a series of tones with a piezo buzzer to indicate temperatures. You could even flash a LED as another cheap alternative.
Another option is to use 7 segment LED displays. If you choose this path, what you save in costs you lose in complexity, because the task of controlling the display is more complex than the LCD units. You can find a circuit diagram of how this might be done here.
Schematic File for editing:
Picaxe08M.sch
Circuit Layout file for editing:
Picaxe08M.pcb
Schematic in GIF format
Circuit Layout in GIF format
Picaxe program - fridge controller
The probes should be moisture proof. Fridges and Mash tuns are hostile environments. A robust solution is to go to any good plumbing outlet, and buy some solder end stops for normal copper water pipe. If you solder this to some pipe, the probe can be placed down the pipe and have thermal contact with mash or fermenter, but be moisture proof.
If you don't have access to the end caps, you can simply put the end of a section of pipe in a clamp to squash it closed. If you clean it and flux it before doing this, the solder will make a nice seal of the squashed end. It is not as elegant as an end cap, but just as effective.
If you don't have the capacity to solder copper pipes then you might use a rubber stopper or even epoxy to seal the end.
