Electronics¶
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.
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.
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).
an airway pressure sensor (Amphenol 1 PSI-D-4V-MINI)
a differential pressure sensor (Amphenol 5 INCH-D2-P4V-MINI) to report the expiratory flow rate through a D-Lite spirometer
an oxygen sensor (Sensiron SS-12A) whose 13 mV differential output signal is amplified 250-fold by an instrumentation amplifier (Texas Instruments INA126)
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.
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:
regulate the 24V power supply to 5V (CUI Inc PDQE15-Q24-S5-D DC-DC converter)
interface the Raspberry Pi with the inspiratory and expiratory valves through an array of solenoid drivers (ULN2003A Darlington transistor array)
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 |