Project 04 · Team lead · Mechanical design

ZEIKU: a blood-sample swab drying system

Ottawa Police labs dry forensic swabs, such as blood samples taken for DNA analysis, by hand and judge dryness by eye. A badly dried swab can spoil the sample, skew results and risk cross-contamination. I led a five-person team through the design, fabrication, assembly and testing of a sealed, portable box that dries two swabs side by side, measures humidity in real time and lights up when each swab is dry.

ClientOttawa Police

CourseGNG1503 · uOttawa

DateOct – Dec 2025

Team5 students

My roleTeam lead

ToolsSolidWorks · Arduino · 3D printing · Laser cutting

19×19×29cm

Sealed acrylic enclosure

≥3cm

Minimum swab spacing, set by our cross-contamination test

2.6CFM

Airflow needed. The 40 mm fan supplies 3 to 5

+2% RH

Dryness threshold relative to ambient humidity

The five-person ZEIKU team standing together, holding the finished acrylic swab dryer — **Fig. 4.1** The ZEIKU team with the finished prototype.

ZEIKU enclosure with the electronics shelf on top, PLA corner brackets and swab holders below — **Fig. 4.2** Electronics shelf above, swab chamber below, on internal rails with PLA corner brackets.

What I did

Led the team through design, fabrication, assembly and testing, and delivered a working prototype that met the client's main objective.
Created SolidWorks parts and assemblies and fabricated the components by 3D printing and laser cutting.
Integrated the Arduino temperature and humidity sensors, then analyzed the drying-test data and reported the findings.

What the client needed

Drying without handling during the process, and no opening the box to check.
Clear, reliable confirmation that a swab is dry.
A compact, hygienic device that is easy to clean.
Automatic temperature and humidity logging to prove the process worked.

Mechanical design

Enclosure: rigid, non-porous acrylic that is easy to disinfect, reinforced with 3D-printed PLA brackets in the corners and along the edges.
Sliding door on rails, so the box opens in one motion without disturbing the samples.
Rail-mounted, removable shelves for the swab holder and the electronics. Everything comes out for cleaning without tools.
Ventilation: 5×5 cm cut-out, 3D-printed fan mount with M3 screws, outer grille and a foam-filter frame, so only filtered air reaches the chamber.

Design decisions

Choice	Picked	Why
Fan size	40 mm	Best flow-to-noise trade-off. 30 and 60 mm were considered and rejected
Filter	Fine foam	HEPA is too restrictive for a small 40 mm fan
Mount material	PLA	Easy to print and not thermally critical, so no need for PETG
Humidity sensors	DHT11	Accurate enough in testing, so the pricier DHT22 wasn't needed
Data link	Bluetooth	The electronics shelf sits inside the sealed box, where a USB cable is impractical

Sizing the airflow

openingA = 5 cm × 5 cm = 0.0025 m²
targetv ≈ 0.5 m/s
flowQ = A·v = 0.00125 m³/s ≈ 4.5 m³/h ≈ 2.6 CFM
supply5 V, 40 mm fan → 3–5 CFM ✓ adequate

Testing

Test	Method	Result
Cross-contamination	Two swabs at 1, 3 and 5 cm, one with a tracer, fan on for 30 min	Contaminated at 1 cm, clean at 3 and 5 cm. Rule: ≥3 cm
Fan mount	5 V fan on its printed mount, flow checked with light paper, noise and stability observed	Steady flow, no excessive vibration, filter doesn't choke the fan
Dryness detection	Wet swab placed under each sensor	Green LED on once dry, on every trial
Data logging	Sensors streamed over Bluetooth to Excel	All readings received and saved

What I'd do next. Hold more than two swabs, bring detection time under 30 minutes, and close the loop with PWM fan control driven by the humidity sensors.

Circuit diagram: Arduino Uno with three DHT11 sensors, a 16x2 LCD, two green LEDs, an HC-05 Bluetooth module and batteries — **Fig. 4.3** Team circuit: Arduino Uno, 3× DHT11, LCD, status LEDs and HC-05 Bluetooth that logs to Excel.

Team leadSolidWorksMechanical designArduino3D printingLaser cuttingAcrylic fabricationAirflow sizingPrototype testingClient needs

Project on MakerRepo ↗

Iteration

From prototype 1 to final

Prototype 1 was tested in November 2025 and reviewed with the client on November 3. Each failure turned into a design change in the final version.

Where it came from	Prototype 1	Final version
Door test	Failed. The removable door hit the top of the box and cracked it on every attempt to close it.	A sliding door that runs in two rails, with the fit and tolerances reworked.
Detection test	Failed. The LED stayed off after the swab had dried, until someone stirred the air by hand.	A 5 V, 40 mm fan keeps filtered air moving past the sensors.
Client review	Fan mounted on the back wall. The client asked for it in the centre.	Fan moved to the centre of the box for more even airflow.
Capacity	One swab sensor and one LED.	Three sensors (ambient plus one per swab) and two LEDs, for two swabs side by side.
Load test	3 mm panels flexed visibly from 7.8 N.	PLA brackets added in the corners and along the edges.
Client review	Approved. Acrylic wipes clean, and the compact size travels well between sites.	Kept.

Load-testing the panels

The 3 mm acrylic panels take the handle load and the knocks of transport. We loaded them in ten steps with water, from 100 mL to 1000 mL (0.98 N to 9.81 N), and watched for deflection.

6.9N

Fully rigid up to this load (700 mL)

7.8N

First visible flex, side panels

8.8N

First visible flex, roof

No permanent deformation at any step, so the acrylic stayed elastic. For a handle that carries the whole box, the recommendation was internal ribs or 4–5 mm sheet.

Checked against the specs

Constraint	Target	Final
Length and width	< 30.48 cm	19 cm ✓
Height	< 40.64 cm	29 cm ✓
Volume, to fit the drying cabinet	< 37,755 cm³	10,469 cm³ ✓
Swab spacing	> 2 cm	≥ 3 cm, tested ✓
Washable material	Non-porous	Acrylic ✓

Prototype 1 on a table during testing, with the green dryness LED lit and the electronics on a shelf inside the acrylic box — **Fig. 4.4** Prototype 1 during testing, with the dryness LED lit.