I have a nice project with a lot of steel and quite some interesting electronics to show you today. This project sprouted from a concrete necessity that I had. I needed a kitchen hood but I wanted it to be hanging in a way that would hover over the cooker without ruining the mosaic tiles at the back of it.
So I decided to build one, I wanted the kitchen hood to be durable so I decided to make it in stainless steel and I wanted it to be basic but technological so what else could I chose if not the great Arduino board to be the heart of it.
I must admit that eventually the final product ended up quite more lavish than what I had expected. I'm very satisfied with it now that I'm using it every day and I hope that you will like it as well and that you will be creative and customize yours if you are going to embark on this project. Unfortunately, this is not a low budget project, as you could easily end up with -500$ in your bank account at the end of it. I have already thought about some improvements that I have added at the end.
This tech project divides into the following sections:
- Concept and sketch
- List of electronic and mechanical parts
- 3D Mechanical design
- Production of mechanical parts (I recommend you delegate this to someone that has a big laser to cut steel)
- Electronic wiring
- Firmware coding
- Final mechanical assembly
- Cooker hood fixing
But before starting:
Disclosure: I am not responsible for any damage that could happen to you if you follow this project.
- This project involves working with AC relays and wiring cables that carry high voltage, 230V in my country. Always double-check all wires to be sure they are connected properly.It is imperative that you test the assembled circuit on an electrical system that has a circuit breaker and grounding; in my county every residential electrical wiring must comply with this two norms. If you get shocked with 230V you won't die but make sure you release the wire immediately if this happens. In a few words: don't end up electrocuted!
- The hardware is going in a place that could get very dirty so it is advisable to use silicone, insulating gel or resin to protect it, as the grease could form a bridge between the electronic contacts and cause a short-circuit.
- Working with stainless steel is dangerous as it require a high power laser to cut it, it is hard to bend and also involve TIG welding to solder the pieces. I recommend that if you don't have all this gear and the skills you ask a well-equipped blacksmith or a company in your area to help you out.
- Once you have the mechanical parts make sure you always use thick gloves during the assembly because steel sharp edges may cause serious wounds.
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Step 1: Concept and Sketch
Whatever you are trying to build it is always better to start on a piece of paper and draw your idea there first.
I decided my cooker to be cylindrical in shape.
I like circular shapes and I also knew that could be made by bending a stainless steel sheet.
I also had to study a bit how a kitchen hood is made, it is basically a three-speed fan that filters the air coming from the cooker trough 2 filters.
- aluminum grease filter, which blocks the vaporized grease
- active carbon filter, which withholds the VOCs, volatile organic compounds, or in other words the "bad odors", which are big molecules with Carbon inside.
Step 2: Mechanical and Electrical Parts
Step 3: Electronic Hardware
- 1 Step-down
- 1 Arduino Uno
- 2 LED lamps, choose the one you like the most
- 1 30W Power supply 24V (I got this)
- 4 Fancy push buttons.
- 4 Fuse holders
- 4 1A 250V fuses
- 2 3 poles shielded cable
- cable with plug
- 2 boxes for the hardware
- heat shrink tubing
Step 4: 3D Mechanical Design
Once that we have bought the things that are going inside the kitchen hood we start to design the chassis in stainless steel sheet. I made it 1mm thick but if you would like a lighter structure you could also go for 0.5mm.
While designing we have to keep in mind the industrial processes to work with metal sheets:
1) Initially I measured with my caliper and ruler all the parts I had bought and I designed them with a lot of approximation:
- the motor
- the grease filter
- the carbon filter
It is important to keep in mind how these elements are going to be fixed, so I included bolt holes in the design.
2) I decided that a good size for the kitchen hood would have been 450mm in diameter and 350mm in height
3) I figured out that there were three main stainless steel parts:
- a cylinder structure in the middle
- a top cap to close the top
- a base with all the supports and brackets for holding the motor and filters
4) Designing the top has been quite straightforward, the top has 6 fixing points with stadiums for M4 bolts and has trapezoid-shaped cuts to let the air flow upwards.
HINT: when you have to join two parts with bolts it is advisable to work with stadiums instead than with holes!
5) The most difficult part to design has been the base, it needed to have all this elements:
- rectangular-shaped opening for the LED lamps, which I made 28mm wide to fit my lamps
- L brackets for the motor
- brackets for the carbon filter
- holes for the push buttons
HINT: when you design something you also have to think how the parts are then assembled together. I had to insert a removable L bracket to allow me to insert the motor.
Feel free to download all the 3D models:
.x_b is the binary file of the complete assembly that can be opened and then modified by any 3D design software such as Solidworks or Inventor, etc.
.stl are the single 3D files which can be analyzed and also opened in Windows 10 to glance at them.
Step 5: Production of Mechanical Parts
Now comes the industrial section.
I link you to a video of what I mean for a "big laser" and you'll need one of those to cut inox steel. I wish I had it, but I don't, so sadly I had the cuttings made by a company, they also made the bending.
I believe that there are many companies that have industrial machinery in your area as well. Sometimes also some well-equipped blacksmiths have this sort of gear.
If you don't know how to weld with TIG I have posted a video that explains that. You can do this yourself or ask the company to do it.
Anyway I'll point out the processes followed for each part:
- Top cap
- laser-cut the shape
- bend with an industrial bender the L fixing supports
- laser cut the rectangular sheet and the holes
- bending the sheet into a cylinder
- TIG welding to close the cylinder
- laser cut 4 pieces of the base: the circle has actually been divided in 4 arches, each following one side of the rectangle in which the aluminum filter fits
- bending with the industrial bender the L-shaped supports and fixing points
- TIG welding
- in order to cover the welding marks it has finally been sanded
Step 6: Electronic Wiring
Now it's time for the messy wiring part.
I hope that the schematics will help you out. I designed it with Solid Edge and I have attached the file in case you wish to modify it.
Assemble the LED lamps which are made of 24V strip LED more and aluminum heatsink and a cover.
As you can see I have used two boxes that I have attached with double-sided tape one on top of the other.
The box on the bottom holds fuses and solid state relays and the one on top contains Arduino, step-down and the MOSFET. If you don't know much about electronics basically a MOSFET is like a controlled switch for DC current and a solid state relay is a controlled switch for AC current. In order to connect everything together you need to do some soldering.
For precaution I have added a general fuse and one for each motor phase so in case of the unlikely event of overcurrent the fuse should do its job and interrupt it.
All hardware is going in a place that could get very dirty with grease and wet with moisture so I recommend you use an insulating spray or a magic gel, or you can also squeeze siliconefor mirrors inside the boxes. Don't use acetic silicone, it would corrode copper!
I have fixed the lamps and wired the push button. You can use 3-pole wires or 4 poles cables. I kept the GND separated.
Make sure you earth the inox steel structure. → THIS IS REQUIRED BY LAW
With every push button I have basically carried around a pin of Arduino, so it is better to shield this cable and connect it to earth. An improvement that I will point out at the end of the guide is to use optocoupler to isolate all the pins of Arduino that are travelling a long distance.
Step 7: Arduino Firmware
Flash the firmware on Arduino and you are done.
I have commented almost every line of code I wrote so if you are curious to know how it works just look inside.
BE CAREFUL!! If you modify or you make a mistake in wiring and two coils of the motor end up receiving current at the same time you will instantly burn the motor. If you change the firmware make sure that the other coils are switched off if you switch on a new one.
Step 8: Final Assembly
BE CAREFUL TO SHARP EDGES!! USE GLOVES!!
- screw and level the 2 lamps
- screw the carbon filter to the motor
- place the motor
- fix the loose L bracket to the motor and to the base with M4 bolts and nuts
- place the cylinder structure
- connect with a connector the Schuko cable to the power supply, use a cable gland to make sure it is not rubbing the steel hole.
- tighten the M5 bolts and nuts to join the cylinder structure with the base
- don't forget to run the hanging steel cable through the holes in the steel cap
- finally place the steel cap on top and in order to tighten its bolts you have to remove the aluminum grease filter, stuck your gloved hand inside it, and tighten the inner nuts from the inside; it is quite hard but a hand fit well inside.
- To fix the cooker hood on the ceiling you have to cut the steel wire of the right length, mine is hovering 85cm over the cooker.
BE CAREFUL!! Cutting steel wire it is not easy. You will need big pincers and you can soften the steel heating it up with a hot air gun or a butane torch.
Step 9: We Made It!
Well at this point you don't need to buy a cooker hood for your kitchen anymore because you already have a stylish one and more importantly the great satisfaction of having made it by yourself.
Congratulations and thank you for sticking around!
Step 10: Improvements and Variations
While I was building the kitchen hood I had many ideas I did not implement but you can add some to your project:
1)Adding a gas and VOC sensor with a Bluetooth Android app made with App Inventor
I have finally decided to build a basic and user-friendly kitchen hood even though initially I thought to connect to Arduino also a VOC and CO2 Sensor and to build an app to monitor the readings via Bluetooth. There are many tutorials on how to receive a sensor reading on App Inventor. For example this one to receive temperature and humidity readings. You just have to adapt that to the CO2 and VOC sensor. Adafruit website is great for that as there is everything explained about the Arduino library and how to read from the sensor, as simple as:
int eCO2 = ccs.geteCO2(); //returns eCO2 reading int TVOC = ccs.getTVOC(); //return TVOC reading
2) Changing the backlit push buttons with vintage-looking metal switches
Initially I wanted to make the cooker hood look vintage and I supposed to use metal switches to turn on the light and the motor speed so I had actually coded the firmware for changing the motor speed with switches. Honestly, it has been quite a headache to write it and I did not find anything similar online. Basically, what it does is: changing 3 speed of a motor according to 3 switches. So if you want to use metal switches (such as the ones in the picture) or backlit switches instead than backlit buttons just make sure you upload the right "metal_switches_firmware" you find on this page.
3) Adding optocouplers
It has been quite risky to bring all that way around the wires connected to the INPUT_PULLUP of Arduino. It is not recommended have a microcontroller pin travelling a long distance as it could be affected by lots of outer noise. So it would be better to optically isolate the control circuit and the pins with optocouplers. I have added a picture that explains how an optocoupler works. Basically it isolates the GND of two circuits so the noises produced in one don't affect the other. It is extensively used in home appliances when you are carrying around the pin of a microcontroller.
4) Use M5 bolts with round head
I really like round head bolts; they would have given the kitchen hood even a smoother and cleaner look. If you would like to use them make sure you design squared-holes to fit them in.
5) Adding an air channel made of plastic sheet
Take a polycarbonate sheet 1mm thick, bend it into a pipe and lock it with aluminum tape or glue. Placing it around the motor fan you can actually better channel the air towards the openings at the top.
This is really the end of it.
Feel free to suggest other improvements in the comments!
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