Οιωνός: DIY HDD conversion to microhematocrit centrifuge

There are so many DIY projects out there that use old HDDs.

I liked the idea of converting HDD to a centrifuge. So I made my version by converting an HDD to a microhematocrit centrifuge.

Microhematocrit is a procedure for determining the ratio of the volume of packed red blood cells to the volume of whole blood by centrifuging a minute quantity of blood in a capillary tube coated with heparin.A centrifuge spins the sample at a very high speed to achieve the separation.

Haematocrit centrifuges are used to measure the volume percentage of red blood cells in whole blood.

The packed cell volume (PCV) can be determined by centrifuging heparinized blood in a capillary tube (also known as a microhematocrit tube).

Particles in a suspension will settle in the bottom of a vessel over time, this is called sedimentation. The particles fall to the bottom due to gravity, in the same way that herbs in a salad dressing settle at the bottom of the bottle. This force is expressed as G. Centrifugation increases the rate of sedimentation (i.e. accumulation of red and white bloods cells in the bottom of a blood tube) by spinning the blood samples and creating a centrifugal force that acts on the particles (in this case, red and white blood cells) [source].

This separates the blood into layers. The volume of packed red blood cells divided by the total volume of the blood sample gives the PCV. Since a tube is used, this can be calculated by measuring the lengths of the layers.

Although, it is proposed to centrifuge sample at 10,000 RPM for five minutes, this is not accurate. The force exerted on a particle in a centrifuge is a simple function of the rotation speed of the centrifuge and the radius of rotation. The actual equation is:

RCF or G-force= 1.12 x R x (RPM/1000)²

RCF:Relative Centrifugal Force
R is the radius of rotation measured in millimetres.

For hematocrit is proposed 45000 RCF (RPM to RCF calculator).

HDD disc has a diameter of 90mm (45mm radius). So, it produces 5040 RCF per minute (at 10000 rpm).
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For this project I used:

- An old HDD
- 3D printer for covers construction
- 20A ESC brushless controller
- ATmega32U4 5V 16MHz
- LCD
- 4 Key pad
- IR sensor
- Potentiometer
- Rocker on/off switch
- A camera dvd (clear plastic).
- Microhematocrit heparinized capillary tubes 70mm. These tubes are too long for this centrifuge. I had to cut the tube in two equal pieces (35 +35 mm)

Back view of centrifuge (Uncovered )

I opened the HDD (there are many articles about opening HDDs). The only parts that I used were the HDD case, the brushless motor and the disc plate.
I made holes for the on/off switch and power.
ESC connected with the brushless motor. I excluded the common pin (3 wires controller). I have to mention that I tried also other esc but couldn't start the motor without a little help. LittleBee 20A OPTO ESC worked just fine.
Installation of arduino board.
Installation of an analog IR sensor to a position under HDD disc, after making a black mark on it. This is going to be used for counting rpm.
IR sensor connected with arduino's analog comparator.