Server Cabinet to Food Dehydrator, Arduino Controlled

We needed to make a bunch of raw food and often that means dehydrating.  To accomplish this we found a server cabinet and turned it into a dehydrator.

This was a pretty simple project and produces a lot of food storage.

Specifications
- Dehydrate at around 115F
- good temperature control (top, middle, and bottom sensors)
- A lot of air movement
- 750 watt George Forman Grill powered

Step 1: Parts and Pices

Major Pieces
Server Cabinet
George Forman Grill (good will or some similar heating device)
Commercial Kitchen Rack and trays
5 volt Power Supply (I used one from an old PC like this)
qty(3) Server Cabinet Fans
2" of rigid insulation around the cabinet

Controls
Arduino Pro by Sparkfun (although any Arduino will work) 
LCD Button Shield by Adafruit or Sparkfun
Dallas Temperature Sensors, qty(3) Sparfkun, Adafruit
5Volt relay by Sparkfun or ebay

Notes:
The relay has to handle 120volts and 10 amps depending on the george foreman grill you get. Just read the specs.

Step 2: Air Flow and Heat Control

The back of the unit has a piece of wood that creates a 3" plenum all the way to the bottom.

Hot air is warmed by the heater, rises to the top of the cabinet, and is blown by qty(3) fans into the plenum.  Air is blown down the backside of the unit and exits next to the heater. (see picture).

In order to help moderate the radiant heat transfer we added tiles above the grill. (see picture).

The front door does not seal to well. This allows quite a bit of fresh air to circulate into the cabinet which is key as moisture evaporating from the food needs to escape.

Step 3: Wiring

Wiring:

1) LCD Shield and Arduino need 5 volts.
2) wire 5 volts, ground, and digital control pin to George Forman Grill relay
3) Wire Server Fans always ON
4) Wire Dallas Temperature Sensors. One towards the top of the unit, one in the middle, and one at the bottom to get an average temperature across the cabinet. 

Step 4: Programming

The program is attached below.  It is a pretty simple program using the Dallas Temperature one-wire library and the LCD Button Shield library.

Dallas Temperature one-wire tutorial is here.
LCD Shield tutorial is here. 

The three temperature sensors are averaged and the grill is turned ON and OFF based on the temperature setpoint.