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Brewing heater interface

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The application I am seeking assistance with is the control of temperature in the mash during the conversion of starch to sugars.

The grain/water mash is held in a picnic cooler at XT temperature for XM minutes.  The temp. is increased to YT for YM and is increased again to ZT for ZM.  Some recipes may have more temperture break points.

My thought would be to pump out at a slow rate the water from the bottom of the cooler and pass it through a heat exchange coil submersed in a couple gallon kettle and return the water to the top of the mash in the cooler.  The temperature in the kettle could be increased with a hotplate or submersible heater.

I envision a microprocessor or computer to read the temperature from a probe and turn on or off a contactor  to control the heat. 

It is a simple concept, but I do not know how to interface the input data to the closing of a switch to activate the controllor.

Assistance would be appreciated.

Thanks,  Greg

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Well, it seems to me that you've got it figured out pretty much by yourself. ;)

Using a Pt100 element on an A/D input on the microcontroller would give you a fairly alright way to monitor the temperature.  Then you could program the microcontroller to sample the temperature as often as you need; once a second, once a minute, once every quarter of an hour etc.  Then you just toggle an output pin high and low to control the submerged heater / hotplate.  Elements like multiple temperature break points and hysteresis for the heater is easily controlled within the microcontroller program.

I'm not a brewer and don't understand the process involved exactly, so please correct me if I'm off on something. :)

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Hi Greg,
First, you would use any temperature sensor that you desire, put it in a sealed container that will allow temperature transfer, and convert this reading to a 0-5 volt reading for the range of the sensor. A micro with on-board Analog to Digital converter will convert your voltage into a digital number. A little calculation and you can turn on a bit on another pin to control a relay. The pin should use a transistor to activate a relay or you can use a solid state relay. A solid state relay would be better since it has no contacts to wear out, but they are a little more expensive.
Another nice feature of using a micro is that you can add an LCD display to monitor the temperature and/or send a signal to the serial port of your computer.


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