The components used in the project

The basic concept is to create a vacuum inside the box by extracting the air. When    we    want    to    open    the    drawer    to    pick    up    our    food,    we    can    simply    press    a button.We   see   the   role   of   each   component   in   this   apparently   simple   process,   but   that requires many interactions.

The Box

To    make    the    Box,    I    chose    Plexiglass     as    a    material    because    it    has    many    positive characteristics.Plexiglass   is   suitable   for   food   and   its   transparency   allows   you   to   see   the contents.This   material   is   very   compact   and   cuts   well   with   the   laser,   the   joints   made   are very precise and have a good anchorage.

In the Week I learned to use the laser cutting machine, I performed tests on the Plexiglass and realized a tetris-inspired interlocking game. It was a very interesting experience to learn the parametric design and how to cut with the laser. This is the link if you want to see what I have done: “Computer-Controlled Cutting : Laser Cutting” Thanks to this exercise, I was able to measure the kerf and find the correct parameters for the processing of my final project: Kerf: 0.1 mm The Laser cutter machine: Speedy 400 by trotec P=100.00 V=0.13 Laser Power=2000 The   best   result   was   :   the   square   of   10.2x10.2   (male   that   reduces   and   becomes   10x10   mm)   the   square   9.8x9.8   (female   that   widens   and   becomes   10x10 mm) we have two cuts …. then 10.2mm - 10 mm =  0.2 / 2 (two cuts)= 0.1 mm kerf .

2D / 3D CAD design

Having   the   parameters   to   perform   the   cutting   of   the   plexiglass,   I   can   begin   to   draw   the   pieces   to   build   my   Box.Thanks   to   what   I   learned   in   the " Computer-Aided Design " week, I realized the project of the external Box and of the internal Drawer, using the Rhino 2D/3D Modeling Software.

Start cutting!

From   the   Rhino   3D   File   menu,   I   can   select   "Export"   and   save   the   cutting   files   in   .dxf   format   to   load   them   into   the   laser   machine   software   and   proceed to   the   cut   after   setting   the   correct   parameters,   this   includes   the   positioning   of   the   plexiglass   on   the   plane,   the   focus   setup   of   the   lens   by   adjusting   the height with the appropriate tool.

Assembling the pieces

Here   we   are   assembling!   This   phase   was   particularly   exciting,   because   the   project   materialized   ...   we   passed   from   the   abstract   to   the   reality   and   this was   very   gratifying.   One   advice   I   can   give   to   all   those   who   decide   to   work   with   the   plexiglass   is   that   this   material   must   be   handled   carefully   because   the corners are particularly delicate .You must be very careful, especially when assembling the pieces , to prevent the cut part from splintering.

Sealing Gasket

To ensure a good closure of the drawer, I thought to create a silicone gasket, using a mold made by cutting a rectangle from a plexiglass waste. I   put   some   tape   to   hold   the   part   to   work,   then   I   removed   only   the   rectangle   leaving   the   vacuum   to   fill   with   the   liquid   silicone.   The   practice   with   these materials and the basic concepts acquired during the " molding and casting " week was useful to me.

Self-built Components

Thanks   to   the   week   dedicated   to   3D   printing ,   I   have   the   necessary   skills   to   make   the   three   pieces   I   need   for   my   project.   The   first   piece   is   the   handle   for the   extractable   drawer,   the   second   is   the   support   for   the   vacuum   pump,   the   third   and   last   is   the   connector   that   allows   me   to   connect   the   valve   and   the silicone   tube.As   I   did   to   design   the   Box,   I   use   the   Rhino   3D   Software   to   create   the   3D   models   of   the   necessary   pieces,   not   within   the   details   of   the realization as it would be off topic, and the procedure is the same as already fully illustrated.

The Vacuum Pump

This   component   does   not   need   many   explanations,   it   serves   to   create   a   vacuum   inside   the   Box.   The   use   of   the   vacuum   pump   is   very   simple,   you   only need   to   supply   a   12V   current   by   connecting   the   negative   and   positive   pole   to   the   motor.To   choose   the   type   of   pump   to   buy,   I   thought   about disassembling   a   vacuum   machine   ( FIG.   C)    that   works   with   the   bags,   which   I   had   at   my   house.In   this   way   I   was   able   to   identify   the   exact   model   and   the brand to order it on the Internet :

The Pump and The Valve :How to Use

In   my   project   I   use   a   relay,   activated   by   the   software   of   my   electronic   board,   to   control   the   start   and duration   of   the   Pump   operation.   Next   we   will   see   the   connection   scheme   with   the   relay.I   have   tested   the solenoid   valve   with   the   pump   and   the   two   relays   to   verify   the   correct   functioning   of   the   components. Below you can view the video of the Test in my Vimeo channel.

The Solenoid Valve

The   role   of   the   Valve   is   twofold.When   the   pump   creates   a   vacuum,   the   valve   must   prevent   air   from   entering   the   Box,   so   it   will   be   closed.   Vice versa,   when   the   button   is   pressed   to   open   the   drawer,   the   valve   will   open   by   letting   in   the   air   which   will   cancel   the   vacuum   seal,   allowing   the drawer   to   open.As   we   have   seen   for   the   pump,   also   the   solenoid   valve   has   simply   two   contacts,   one   per   pole,   equally   controlled   by   a   relay that   is   activated   and   timed   by   the   software   of   the   electronic   board.   The   valve   has   two   threaded   sides   and   the   electrical   part   is   closed   inside   a plastic body. ( FIG. D)  

The Relay

A   relay   is   an   electrical   switch   that   closes   or   opens   a   circuit   thanks   to   an   electrical   impulse.In   my   project,   I   used   two   relays   to   control   the   start   of the vacuum pump and the solenoid valve.The relay seen from above has connections on both sides.( FIG. E)   On the left side we have three contacts, VCC = + 5v, GND = - Negative, In = inpulse on digital pin. These   contacts   are   connected   to   my   electronic   board.   On   the   right   side   we   have   three   screw   connectors,   NO   =   Normally   Open,   COM   = Common   Port,   NC   =   Normally   Close.The   central   part   (COM)   is   the   power   supply   current   of   12V   Dc   that   comes   from   the   220vAc-12VDc transformer.In   my   project   I   used   the   NO   (Normally   Open)   output   because   I   need   to   activate   the   component,   if   I   needed   to   interrupt   a   current flow, I would have used NC (Normally Close).

The Magnetic Sensor

This   component   is   fundamental   because   it   allows   the   software   to   check   if   the   drawer   is   open   or   closed.The   sensor   is   placed   at   the   top   on the   right,   in   the   front   part   of   the   Box,   where   the   opening   for   the   drawer   is   located.On   the   upper   edge   of   the   front   of   the   drawer,   in   the upper right corner, there is a small magnet. (FIG. F)   The   magnetic   sensor   detects   the   presence   of   the   magnet   and   sends   a   different   reading   of   the   value,   this   variation   is   interpreted   by   the software   and   allows   to   manage   the   dynamics   of   the   program.During   the   "Input   Devices"   study   week,   I   learned   how   to   manage   this   sensor, both for hardware and software.

http://fab.academany.org/2018/labs/fablabsiena/students/giuseppe-allocca/input%20devices.html

In   the   first   use   I   made   a   trivial   mistake   and   for   this   I   had   to   create   a   new   card.   I'm   glad   I   was   wrong,   because   the   new   version   of   the   card was   useful   for   the   final   project.   My   mistake   was   to   connect   the   magnetic   sensor   to   a   digital   pin,   this   is   wrong   because   the   sensor   needs   an analog pin. Please keep this in mind if you want to use this sensor in your project!

How to Use The Sensor:

The Pin-out Diagram ( FIG. G ) shows the three sensor pins, which are: vcc +5  (pin1),  -GND (pin3), VOUT (pin2). This   last   pin   (Value   Out)   is   the   one   that   will   return   the   value   read   by   the   sensor,   sensitive   to   the   magnetic   field   of   the   magnet   glued   on   the front of the drawer, and read its value using an analogue input in our circuit.

Push the Button!

Although   it   is   an   extremely   simple   component,   the   button   has   the   function   of   sending   the   opening signal   to   the   electronic   board,   which   activates   the   valve   to   eliminate   the   vacuum   and   allow   the drawer to open. The button has three pins: + 5V , - GND, OUT (to Digital Pin) I chose to place the button on the top of the Box, on the right side. Obviously, the position can be changed, but it must be a convenient position to use.

The Main Board

The   heart   of   everything   is   the   electronic   board   that   constantly   controls   the   status   of   the   button   and   the   sensor,   the   programmed   algorithm understands   if   you   want   to   open   the   drawer   or   if   we   have   closed   it.For   more   details   about   the   Software,   please   refer   to   the   dedicated   page. Here is the link: Box Food Saver Software Page As      I      have      learned      in      past      weeks ,      to      create      my      electronic      board,      I      have      used      the      “Eagle”      software      to      prepare      the      schematic      ( FIG.   H )     and      the      electrical   connections      named      Board      ( FIG.   I ).      For      this      board      I      decided      to      have      more      pins      available      for      further      development.     I think it is useful to multiply the power and ground pins in more contacts and also have extra pins available. The Microcontroller chosen for the realization of the control board is ATMega328p TQFP  (as indicated in the list of components FIG. L ). I   decided   to   use   this   processor   because   it   offers   many   pins   to   use   and   I   like   this   because   I   can   foresee   possible   additional   sensor   connections and more. For more details on the creation of the card, this is the link: Board

Test of Final Project

Completed   the   wiring   of   all   the   components,   the   time   has   now come   to   test   the   Box   Food   Saver   to   see   if   it   works.   First   we   give power,   connecting   the   plug   of   the   power   supply   to   the   220v   home network (Italy). I   close   the   drawer,   the   sensor   detects   the   magnet   on   the   edge   of the   drawer   and   sends   a   different   value   on   the   analog   pin,   this value    is    processed    by    the    algorithm    that    starts    the    vacuum pump.To   test   the   button,   I   press   it   and   the   software   understands that   I   want   to   open   the   drawer,   then   the   board   sends   the   signal   to the   relay   that   opens   the   solenoid   valve.   At   this   point   the   air   can enter   the   box   and   I   can   open   the   drawer.   The   software   part   works well and the hardware responds to commands.

Wiring of components

In   order   to   simplify   the   wiring   process   I   created   this   ideographic   scheme.( FIG.   N) .    The   components   are   clearly   identified   and   also   their interconnections.   It   is   fundamental   to   remember   that   the   electronic   board   receives   current   from   the   voltage   regulator   and   NOT   directly   from the   power   supply   because   the   voltage   12V   would   burn   the   board.   The   vacuum   pump   and   the   solenoid   valve   receive   electricity   from   the   relays and   NOT   directly   from   the   power   supply.   The   two   relays   and   the   button   communicate   with   the   Board   via   a   digital   pin.   The   magnetic   sensor sends to the board the value detected by the proximity of the magnet, through an Analog pin.

Voltage regulator from 12v to 5v

The   power   supply   purchased   for   the   project   delivers   12v,   this   because   the   pump   and   the   valve   work   at   12v.   My board   works   at   5v   and   therefore   it   is   necessary   to   reduce   the   voltage   to   avoid   burns.   At   this   point,   the   ZLDO   17- 50   voltage   regulator   comes   into   play.   This   small   but   ingenious   component   allows   the   card   to   work   without suffering   damage,   and   the   output   voltage   that   I   detected   with   the   voltmeter   is   very   stable.   The   component   has three   pins,   looking   at   it   from   the   side   that   shows   the   written   code,   on   the   left   we   find   -GND,   at   the   center   +   5v   the reduced and stabilized voltage, on the right the input of the 12v voltage coming from the power supply.

Problem to Solve

Despite   everything   seems   to   work,   I   realize   that   the   closure   of   the   drawer   is   not   perfect,   despite   the   silicone   gasket.   I   tried   to   increase   the   pump action   time,   but   it   does   not   change   anything.   The   evidence   shows   that   air   enters   the   Box.   The   problem   is   that   air   passes   through   the   joints.   This   is a   big   problem,   if   the   vacuum   does   not   it's   good,   food   preservation   is   also   compromised.I   tried   to   seal   the   joints   with   silicone   and   even   with plexiglass special glue, but air continues to enter the box. The real problem is that even a very small space is enough to compromise the tightness. When   I   presented   my   project,   Neil   Gershenfeld   suggested   that   I   weld   the   joints   by   melting   the   plexiglass   with   hot   air.   This   was   a   simple   but brilliant idea. Unfortunately   I   could   not   implement   this   important   change   in   my   project,   because   after   the   presentation   I   moved   to   another   country   for   work.   As soon as I get the chance, I want to try and implement this suggestion and see if the problem is solved.

Power Supply 220AC to 12V DC

The   power   supply   supplies   the   current   to   the   board   (via   the   voltage   regulator),   to   the valve   and   to   the   pump   (passing   through   the   relays).   For   my   project   I   chose   this model.( FIG. M)   The following are the technical characteristics: Input AC 110/220V. Output: DC 12V. Amperage: 5A. Power: 60W. L N GND = 110/220V Input -V +V = 12V DC Output +V AD J= Voltage fine regulation

Final Conclusion

The   project   is   certainly   interesting   and   may   have   further   developments.   For   this   reason   I      decided      to      distribute      my      software      (Arduino      codes...)     and      hardware      (STL,      Eagle      files...)      components      that      I      realized      under      license      Creative      Commons   Attribution,      in      the      NonCommercial- ShareAlike  4.0  International  (CC  BY-NC-SA  4.0)  variant.  This      kind      of      licence      allows      anyone      to      share      (copy      and      redistribute   the      material      in      any      medium      or      format)      and      adapt      (remix,      transform,     and      build      upon      the      material)      my      works,      on      condition      to      don't      use      them      for      a   commercial   purposes   and   to   give   appropriate   credit,   link   the license   and   indicate   every   changes   made.I      chose      this      license      because      my      project      was      born      to      reduce      the      waste      of      food,      I      think      that      this     way  is  better  and  easier  to  improve  the  project  and  its diffusion. At the bottom of this page you will find the Zip file icon, simply click to download.

Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.