Why buy a dehydrator and spend time modifying it if you already own everything needed to build your own [ fancy / overkill / g-code driven ] filament dehydrator oven ?

Needed parts :

• 1 x arduino mega 2560 r3 board
• 1 x ramps 1.4 board
• 1 x 2004 LCD with encoder and SD card slot
• 2 x 40 mm 12V fans
• 1 x 500W ATX power supply
• two pairs of mini tamyia connectors with 10mm silicone wire
• two pin dupont connector with 20cm of red/black wire - for powering fans
• three pin dupont connector with 20cm of red/back/yellow wire - for controlling the ATX power supply
• 1 x 100k NTC thermistor
• 1 x MK2Y 220mm round 12V PCB heated bed
• 3 x M3x10 bolts - for securing the heatbed
• 3 x M3 nuts - for securing the heatbed
• 6 x M3 washers - for securing the heatbed
• 4 x countersunk wood screws for the ramps case lid
• 4 x countersunk wood screws for the lcd case
• 1 x FAT32 formatted SD card - for running g-code
• 1 x 3D printed case for arduino + ramps
• 1 x 3D printed lcd case (https://www.thingiverse.com/thing:35438)
• 1 x round cookie box (big enough to fit the 220 mm heatbed and one spool of filament)
• 1m of 12 AWG wire
• 1 x self tightening electrical connector (heat resistant)

Needed tools & materials:

• wire strippers
• wire insulation
• soldering tool
• soldering wire
• 2 mm thick cork sheet
• glue
• drilling machine

Needed skills:

• basic electronics understanding
• basic soldering skills
• time and patience

Programming :

• arduino 1.8 (https://www.arduino.cc/en/Main/Software)
• the firmware (https://www.thingiverse.com/download:4089572)

Assembly :

• This is more or less 3D printer hardware and if you ever assembled a kit you know already what needs to be done.
• Pay attention to electrical wiring / soldering and also for good performance to insulation of the cookie box. Please do not solder wires that will be tighten down with screws ! Also use the mini tamyia connector pairs inverse one from another so you don't accidentally mismatch the thermistor with the 12V heating power.
• The firmware is a little bit modified for aesthetics reasons, but otherwise a standard Repetier v 0.92.9 which i've chosen over Marlin for ease of web configuration.
• Don't forget to PID calibrate the heatbed which is done on Repetier firmware with : "M303 P1 S70 R8" for 8 cycles at 70 degrees.
• On the file section you will find also a zip file (https://www.thingiverse.com/download:3913246) with a demo 1m g-code sample and also 1h 2h 4h g-code samples to dry your filament at 70 degrees Celsius.

Power draw :

• min : idle ATX power supply off, fans off : 1.5W
• max : heating up at full power : 100W (the first 2-3 minutes)
• med : PID controller stabilized heating : ~ 40W (the rest of the process)

Results :

• initial ambient humidity : 40%
• 4h for one spool of ABS : 15% humidity
• 8h for one spool of ABS : 10% humidity

Humidity was monitored with an arduino connected to 2 x DHT11 + 2 x DHT22 sensors.