Welcome to our drafting section: He you will find all of the different steps we took to design our olfactometer. starting with a general setup, then the different ideas we presented to the lab and the one that was chosen. You can also find how we constructed our device, especially the 3D printing part.
Enjoy!
Overall Setup
We have conducted a literature search on state-of-the-art olfactometers and recent advances in the field. Based on this research, we formed the general overview of the setup seen in Figure 1 below. The olfactometer itself would consist of four components; a piping unit used for the transfer of airflow, an odor unit consisting of vials containing liquid odor, a sensor unit containing the necessary instruments such as a flow meter and a temperature sensor, and finally a control unit where the flow delivery and distribution is controlled. The setup would include sections outside the olfactometer; such as a source of air, the arena where mice would be situated, and an interface between the instrument and users for the interpretation of certain values.
Based on this scheme, we have created several setup designs that would satisfy our project goals.
An essential part of the design is the valves. We have implemented two types of valves in all designs; solenoid and non-return. Solenoid valves are electromechanically operated valves that can be used as a control in fluidics. They can close and release using a specific controller. In our project, we used Arduino UNO R3 microcontrollers since they are reasonable in price and easy to implement. Non-return valves allow the fluid to flow only in one direction, so we used them to prevent the backflow of air.
First Design Idea
The first design idea is a rather simple setup that serves as a base for other ideas. It involves a main tube connected to the pressure tank of the animal. This tube is then connected to two other tubes to connect the odor liquid. On the main tube there is a solenoid valve placed right after the pressure tank and after the entrance to the tubes attached to odor liquid. Moreover, solenoid valves are placed after the odor vials so that odor distribution to the animal could be controlled. Return valves are placed before the odor vials and after each tube connection to prevent contamination of the air tank, and odor vials.
Second Design Idea
The second design idea is very similar to the first design and created based on the work of Bodyak et al.. The only additions are a filter, a flowmeter, and a ventilation fan in the arena where the animal is located. Flowmeter is added to have better control of the flow, with this addition; flow can be measured and it can be kept at the same value which could increase the accuracy of the results. A filter is added to the design to remove moisture, odor, and particles in the air. A ventilation fan is connected to the arena to remove the odor from the arena so that other odors could be sent to the animal.
Third Design Idea
The third design idea contains an air pump and two manifolds. They are used for the connection of tubes in a more organized manner. This design was made based on a two-channel olfactory distributor design made by Med Associates. In their design, they implement fresh air in the middle tube but we didn’t think that it would be useful, that’s why we decided not to implement it in our final design.
Fourth Design Idea
The fourth design idea is based on the design of Hojjati et al. which has a flowmeter in addition to the third design idea. In this design, researchers decided to use a humidifier bottle to improve the contact of the liquid with air.
After the discussion with the lab group, we made a decision on the final design idea. It would be very similar to the second design idea involving a flowmeter and a filter. We decided not to implement the manifolds to make the design more customizable. The next step is to start building the most essential components of the design and once that is completed and tested, a filter and a flowmeter could be added additionally to improve accuracy.
Specifications of our Device
Several aspects were discussed with the lab regarding the requirements of our olfactometer. Firstly, the device should be able to deliver 2 odors independently, it should have a purging system to clean the tube of the odor. The two odors that will be used are carvone and acetophenone which are almond and mint. The air would travel through Teflon tubes and would be blocked or not by solenoid valves. The valves will be controlled via the microcontroller Arduino. To implement the interface, Firmata library will be used to connect Arduino to python. The required and suggested specification of our device can be found below
List of Requirements and Suggestions
| Required | Suggested |
| Odors | Experimental Protocol |
| At least two odors | Led visual feedback |
| Delivered one at a time | Soda-lime glass beads inside the vials |
| Purging of pipes | Odor regulator |
| Odor vials with caps | Add-On Component |
| Air Flux | Air filter |
| Air pressure control | Mass flow cytometer/Flow switch/Flow meter |
| Teflon tubes as narrow as possible | Electronics fast gauge |
| Fittings and connectors | Printed circuit board |
| Solenoid and return valves | Mouse |
| Setup Control | Head mask |
| Microcontroller used for solenoid valves and sensor management | Arena |
| User interface | Ventilation |
3D Model
Relay board
The next step in our design process was to construct a model allowing us to place the vials, tubes, valves, and electronics. This setup would be compact, light, and portable. We started with designing a base for the relays which would separate them from the floor. We also used this as an opportunity to get familiar with CAD drawings. The base covers the bottom of the relay and it connects to another relay with the connectors on the vertical sides. Additionally, it contains 4 holes on the edges to connect the board with the relay.
The Vial Stand
As we gained more experience in CAD design we focused on designing the compartment that would carry the vials and the valves. Our goal was to create a structure that could hold the vial and connect it to the valve via tubes. To achieve this, we came up with an L-shaped structure that surrounded the vial and connected it to the valve. The valve is then linked to the relays located on the bottom layer by connecting its cable through a hole in the holder. We designed this compartment to have one odor per unit, with each odor connected to a specific valve. This means that the compartment was made for each odor, allowing for easy modification when required.
Bringing the Components Together
Once the design of the vial compartment was complete, a second section identical to the first was attached right next to it. This was necessary to have two different odors for the experiments. Since the valves and relays need to be connected to the Arduino via the pins, we wanted to construct a box specifically for the Arduino and the pins. The box was designed to be large enough to fit the Arduino Uno and the soldering board, and tall enough to allow space for pin connections.
Improvements
After receiving the tubes and connectors, we placed them on our model to test whether everything fit or not. However, during testing, we noticed that the non-return valves were larger than expected and the PTFE tube was very rigid. For that reason, we decided to modify our design slightly to ensure all materials could be accommodated. The length of the design was extended, and the width was widened to make space for the materials. Additionally, we added holes to attach the three non-return valves and two T-connectors to the box.
Some of our walls are green because of the shortage in metallic silver PLA in the open lab 