ADI Trinamic Open-Source Ventilator

Why Build an Open-Source Ventilator?

The global outbreak of COVID-19 pushes healthcare systems around the world to their limits and medical companies are working hard to produce the much-needed medical equipment. Besides supporting all sorts of ventilator projects, we also want to inspire engineers and medical companies with other ways to design a medical ventilator. That's why we started our own project as well, named TOSV - Trinamic Open-Source Ventilator.

The Concept

Our approach for the Trinamic Open-Source Ventilator is to use CPAP blowers. The reason to use these blowers is twofold: first, we have a lot of experience with low-inductance motors and second, they are still widely available. Normally used in CPAP devices for a continuous flow, you can overdrive them a bit so you have the performance needed for a medical ventilator.

An initial setup was created using the open-source evaluation boards together with open-source software designed especially for the TOSV project. To control the flow, pressure sensing relays back to the controller for respiratory pressure. Differential pressure sensing is also supported for flow-sensing at the patient-side. This way, the design basically does everything required for a medical, blower-based ventilator.

Proof of Concept

The Open-Source Design

After the concept proved to work on a hot-water bottle that simulates a lung, Trinamic started designing an open-source module based on the TMC4671-EVAL-KIT. The small, integrated PCB has a fully integrated software-stack that can be controlled via UART. That way, it can quickly be integrated into designs by medical Engineers.

The miniaturized open-source module handles all the driver functions, as well as the interface to the pressure sensors. A simple single-board computer like a Raspberry Pi or similar can be used for control, which are off-the-shelve available and come with a comfortable user interface and safety functions.

Developing Hardware and Software in Parallel

To have a working concept as quickly as possible, we developed hardware in parallel with software. This was possible by using the Evaluation Kit concept. By combining the Landungsbrücke interface board with the TMC4671 evaluation board and the TMC6100 evaluation board, the complete system architecture including sensors and fast control loops was designed in just a few days. And since all motor control is already integrated in the TMC4671-LA servo controller IC, we had a working proof of concept within a week.

At the same time, our team in Tallinn, Estonia, integrated the evaluation kit setup we used into a single PCB. Incorporating the TMC4671-LA and TMC6100, the module integrates all control functions for the open-source medical ventilator. As for the form factor, we made sure it can be stacked on a Raspberry Pi, which is an easily available single-board computer and perfect for our open-source medical ventilator platform. All files for the open-source design, as well as the software to control the board, can be found on our Github repository.

The Goal

Our goal is not to produce medical ventilators. Our goal with the TOSV project is to have a fast response by offering something that can be mass-produced on the short term and offers high-quality ventilation. By using CPAP blowers, the production of existing medical ventilators won’t be under further strain than it already is due to the coronavirus.

As with all our evaluation boards and breakout boards, the TOSV board is completely open-source. This way, medical companies designing ventilators can take our input and see if it works out for them or not. We simply want to show what's possible and contribute any way we can. All files can be found below and on our GitHub.

Open-Source TOSV Documentation

What Does Ventilation Have to Do With Motion Control?

The core function of a mechanical ventilator, as the name implies, is motion control. A ventilator must exercise tight closed-loop control of a blower in response to various sensor inputs in order to effectively mimic the function of the human respiratory system.

Some common sensors used for feedback in ventilators are pressure sensors, flow sensors, temperature sensors, and humidity sensors. Temperature and humidity sensors are used to measure environmental parameters, while pressure and flow sensors are used for patient-specific variables, including Positive End-Expiratory Pressure (PEEP), Respiratory Rate, Tidal Volume, FiO2, and others. Ventilators also use feedback from current sense amplifiers to measure the current running through the blower.

In addition to responding to various feedback signals, the ventilator also must be capable of driving the blower to support a number of different 'modes', or types of respiratory support. Examples include Assist/Control (A/C), Spontaneous Intermittent Mandatory Ventilation (SIMV), and Volume-Controlled Ventilation (VCV). Each of these modes has slightly different requirements regarding motor drive that make some of the integrated functions of the Trinamic drivers attractive for this kind of application.

Both the images for the hardware package and the open-source software are online and readily available at Trinamic’s GitHub. All medical companies and Engineers, Makers and other interested people are welcome to use it for their own project.

Besides the TOSV project, Trinamic’s R&D and Field Application Engineers continue to fast-track support requests that are related to the coronavirus in an effort to help any way possible.