IEEE Circuits and Systems Magazine - Q3 2021 - 74

Mechanical structure is based on three bellows made
from inner tire tube replacing the AMBU bag that is often
used in artificial ventilators [4]-[7]. Apart from being
easier to supply, using home-made bellows instead
of AMBU bags add reproducibility to the system, since
AMBU bags are quite different from each other, depending
on the local provider. These differences have
a highly negative impact on the maximum tidal volume
capacity, which undermines the control system. Each
bellow uses two limits sensors as shown in Fig. 2 and
is operated by a three 3D printer stepper motor using
fishing wire. Office rubber bands are used for repositioning
bellows in their maximum volume position.
Air or gas is directed by garden hoses and watering
couplers, allowing important cost reduction, as well as
easy implementation.
IV. Electrical Architecture
Figure 1. Artificial ventilator being tested with an artificial lung.
Limits Switch
Sensors
Bellows
Limit Switch
Sensors
Figure 2. Mechanical architecture of the artificial ventilator.
Proposed electrical architecture is presented in Fig. 3.
Supplied with a hand-held power tool battery delivering
18 V DC, electronic system control is based
on a Microchip PIC24FJ64GB004 microcontroller.
There are two main sensors in the design: Silicon
Micro Structures SM6221 for monitoring intra-lung
pressure, and Omron D6F-PH0505AD3 for monitoring
inspired tidal volume using a home-made Pitot
tube, both connected in I2C. Omron D6F-PH0505AD3
is a precise differential pressure sensor having a
measurement range from −50 to 50 Pa, allowing to
build a Pitot tube as shown in Fig. 4. Measured differential
pressure PT is converted into air velocity
using Euler equation [8]. Using fluid velocity and
knowing hose pipe section, inspired volume D can
be calculated as shown in Eq. 1, where t0
of compression, t1
SPipe
is the start
its end, VAir
the hose pipe section.
Ultra Low-Cost Artificial Respirator
Power Source
PC
User Interface
Visual Interface
Control Interface
RS232
PIC24FJ64GB004
12C
Limit
Sensors
Volume
Sensors
(Pitot Tube)
Figure 3. Electronics block diagram.
74
IEEE CIRCUITS AND SYSTEMS MAGAZINE
THIRD QUARTER 2021
Pressure
Sensor
(SM6221)
3D Printer Motors
(103H5208-5240)
Motors
Driver
(A4988)
Embedded System
the air velocity and

IEEE Circuits and Systems Magazine - Q3 2021

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