Electronics

images/electronics_diagram.png

PVP block diagram for main electrical components

The PVP is coordinated by a Raspberry Pi 4 board, which runs the graphical user interface, administers the alarm system, monitors sensor values, and sends actuation commands to the valves. The core electrical system consists of two modular PCB ‘hats’, a sensor PCB and an actuator PCB, that stack onto the Raspberry Pi via 40-pin stackable headers. The modularity of this system enables individual boards to be revised or modified to adapt to component substitutions if required.

We outsourced our PCB fabrication to Advanced Circuits, based out of Aurora, CO (for $33 each): https://www.4pcb.com/pcb-prototype-2-4-layer-boards-specials.html If you would like to do the same, you can send them the Gerber .zip files we have provided directly.

Power and I/O

The main power to the systems is supplied by a DIN rail-mounted 150W 24V supply, which drives the inspiratory valve (4W) and expiratory valves (13W). This voltage is converted to 5V by a switched mode PCB-mounted regulated to power the Raspberry Pi and sensors. This power is transmitted across the PCBs through the stacked headers when required.

Power and I/O bill of materials

Part

Description

Meanwell 24 V DC Power Supply

DIN Rail Power Supplies 150W 24V 5A EN55022 Class B

Raspberry Pi

Raspberry Pi- Model B-1 (1GB RAM)

USB-C Charger/cable

To power the RPi

Micro SD Card

SanDisk Ultra 32GB MicroSDHC UHS-I Card with Adapter

Raspberry Pi Display

Matrix Orbital: TFT Displays & Accessories 7 in HDMI TFT G Series

HDMI for Display

Display cable: HDMI Cables HDMI Cbl Assbly 1M Micro to STD

Mini USB for Display

Display cable: USB Cables / IEEE 1394 Cables 3 ft Ext A-B Mini USB Cable

Screen mount thumb screws

SCREEN_MOUNT_THUMB_SCREW: Brass Raised Knurled-Head Thumb Screw, 1/4”-20 Thread Size, 1/2” Long

Cable grommet

USER_INTERFACE_CABLE_GROMMET: Buna-N Rubber Grommets, for 1-3/8” Hole Diameter and 1/16” Material Thickness, 1” ID, pack of 10

Cable P-clip

USER_INTERFACE_CABLE_P-CLIP_0.375_ID_SS: Snug-Fit Vibration-Damping Loop Clamp, 304 Stainless Steel with Silicone Rubber Cushion, 3/8” ID, pack of 10, 17/64 mounting holes

Keyboard

Adesso: Mini keyboard with trackball

Sensor PCB

The sensor board interfaces four analog output sensors with the Raspberry Pi via I2C commands to a 12-bit 4-channel ADC (Adafruit ADS1015).

  1. an airway pressure sensor (Amphenol 1 PSI-D-4V-MINI)

  2. a differential pressure sensor (Amphenol 5 INCH-D2-P4V-MINI) to report the expiratory flow rate through a D-Lite spirometer

  3. an oxygen sensor (Sensiron SS-12A) whose 13 mV differential output signal is amplified 250-fold by an instrumentation amplifier (Texas Instruments INA126)

  4. a fourth auxiliary slot for an additional analog output sensor (unused)

A set of additional header pins allows for digital output sensors (such as the Sensiron SFM3300 flow sensor) to be interfaced with the Pi directly via I2C if desired.

images/pressure_rev2_schematic_image.png

Sensor PCB schematic

Sensor PCB bill of materials

Ref

Part

Purpose

J1

40-pin stackable RPi header

Connects board to RPi

J2

4-pin 0.1” header

I2C connector if desired

J3

2-pin 0.1” header

Connects ALRT pin from ADS1115 to RPi if needed

J4

3-pin 0.1” header or 3 pin fan extension cable

Connects board to oxygen sensor

R1

330 Ohm resistor

Sets gain for INA126

C1

10 uF, 25V

Cap for TL7660

C2

10 uF, 25V

Cap for TL7660

U1

TL7660, DIP8

Rail splitter for INA126

U2

INA126, DIP8

Instrumentation amplifier for oxygen sensor output

U3

Amphenol 5 INCH-D2-P4V-MINI

Differential pressure sensor (for flow measurement)

U4

Adafruit ADS1115

4x 12-bit ADC

U5

Amphenol 1 PSI-D-4V-MINI

Airway pressure sensor

U6

Auxiliary analog output sensor slot

Actuator PCB

The purpose of the actuator board is twofold:

  1. regulate the 24V power supply to 5V (CUI Inc PDQE15-Q24-S5-D DC-DC converter)

  2. interface the Raspberry Pi with the inspiratory and expiratory valves through an array of solenoid drivers (ULN2003A Darlington transistor array)

images/actuators_rev2_schematic_image.png

Actuator PCB schematic

Actuator PCB bill of materials

Ref

Part

Purpose

J2

2-pin screw terminal, 5.08 mm pitch, PCB mount

Connects to 24V supply

J3

2-pin screw terminal, 5.08 mm pitch, PCB mount

Connects to on/off expiratory valve

J4

2-pin screw terminal, 5.08 mm pitch, PCB mount

Connects to inspiratory valve, driven by PWM

J5

40-pin stackable RPi header

Connects board to RPi

J6

2-pin 0.1” header

Jumper between 5V and Raspberry Pi

C1

100 uF, 16V

5V rail filter cap

C2

6.8 uF, 50V

24V rail filter cap

C3

6.8 uF, 50V

24V rail filter cap

U1

ULN2003A

Darlington BJT array to drive solenoids

U2

CUI PDQ15-Q24-S5-D

24-to-5V DC-DC converter