The aim of the project is to develop a simple, low cost ventilator that can be assembled quickly in large volumes to aid hospitals in their fight against the COVID-19 outbreak. The complete system can be found at https://breathney.cc
The control electronics are based on 2 redundant Arduino compatible microcontrollers of type Atmega2560 which exchange status and operational data over a serial link that also functions as a keep-alive signal. The delegated tasks include keypad controls, LCD display, microswitches, pump/motor control, sensory inputs, user USB control, and sound/light indicators.
As LCD display, most compatible LCD or TFT displays with a 40 pin, 0.5 mm pitch FFC cable can be used. The graphics driver is a RAIO RA8875L3N, which supports up to 800x480 px in display size and a colour depth of 16 bits. It has a high speed serial interface and resistive touch screen support.
The pump/motor driver is a VNH3SP30 from ST, a full bridge driver with a current rating of 30A. It supports 12V and 24V power input. It is fused to 30A with an automotive blade fuse that can be easily sourced from different suppliers.
The sensor inputs are all I2C based, although for ease of connectivity a standard 4 wire USB connector scheme has been chosen to wire up to 5 individual sensor boards to this main board. All sensors share the same I2C bus and are addressed individually. To overcome capacitance on the bus caused by long cables (up to 2 m), a P82B715 buffer has been implemented on either side of the USB connection as line driver.
The actual USB connection, implemented as a USB-B connector, provides connectivity with a host computer to stream performance data and support remote operations. Since neither of the on-board microcontrollers has support for a native USB interface, USB connectivity has been implemented using a dedicated USB to UART bridge, provided by a Silicon Labs CP2102N.
Note that this board is provided "as is" without any form of medical certification, because the rapid evolution of the COVID-19 outbreak made it impossible to complete the lenghty certification process. This design features numerous redundant circuits as fail safes, and was designed as good as possible considering the short deadline, but there is no guarantee that it is free of errors.
Many thanks to Roald Van Glabbeek, Thomas Lapauw, Rayan Rebahi, Jeroen Schelkens, Ewald Van Belle, Thibaux Vannerom, Ronan Beauthier, and Angel Solé for their contributions to the schematics designs that led to this board.