Thanks to the virus crisis, lots of people are designing makeshift ventilator designs in the hopes of saving people’s lives. Many of these are based around some sort of Arduino-powered CPU. [Armstrong Subero] things that’s a great idea, but cautions that making an electronic pair of dice is a different proposition than creating a machine to breathe for someone. But he isn’t just complaining. He talks about considerations when building a real-time and safety-critical system.

[Armstrong] has a lot of good points, although we aren’t sure you need the complexity of a real-time operating system just to squeeze a bag. If anything, that seems like it might make it more susceptible to unexpected operation. However, we agree with his comments that you should have closed-loop control to make sure the device is working, alarming when the device isn’t working, and watchdog timers to guard against lockup.

One excellent point from the post:

For example a high availability system real time system may be specified as having an up time of around 99% in a 24 hour period. Which 1% of the day is it acceptable to have the ventilator not operational? Since we have 1440 minutes in a day, which 14.4 minutes of the day should the patient not be allowed to breathe?

However, he does have some solid suggestions such as using an IDE with debugging and adhering to a coding standard such as MISRA. Of course, he also points out you might choose a different CPU that has safety-critical certifications and corresponding libraries. One suggestion is to have multiple CPUs, and this is a common enough solution in many safety-critical systems. For example, imagine 3 CPUs driving a switching circuit that requires a low logic level to turn on.

You could make the outputs go to inputs if the CPU wants to not drive the switch, or pull the output to ground if it does. Then a pull-up resistor holds the state high if no CPU pulls it to ground. All CPUs could sense the state of the line and if they don’t think it looks right they sound their own alarm. Some systems vote so that two of three CPUs must agree (at least) or, in some cases, three out of five.

We’ve been talking about ventilators quite a bit lately. The kind of mechanical design [Armstrong] is probably thinking of is like the MIT design we talked about last week.

Space. The final frontier. Unfortunately, the vast majority of us are planet-locked until further notice. If you are dedicated hobbyist astronomer, you probably already have the rough positions of the planets memorized. But what if you want to know them exactly from the comfort of your room and educate yourself at the same time? [Shubham Paul] has gone the extra parsec to build a Real-Time Planet Tracker that calculates their locations using Kepler’s Laws with exacting precision.

An Arduino Mega provides the brains, while 3.5-turn-pan and 180-degree-tilt servos are the brawn. A potentiometer and switch allow for for planet and mode selection, while a GPS module and an optional MPU9250 gyroscope/magnetometer let it know where you are. Finally a laser pointer shows the planet’s location in a closed room. And then there’s code: a lot of code.

The hardware side of things — as [Shubham Paul] clarifies — looks a little unfinished because the focus of the project is the software with the intent to instruct. They have included all the code they wrote for the RTPT, providing a breakdown in each section for those who are looking to build their own.

There is an extra step to auto-align the RTPT to north, otherwise you’ll have to do so manually. But [Shubham Paul] has designed it so that even if you move the tracker about, the RTPT will readjust its calculations in real time. Each part of the project includes a wealth of related information beyond simple instructions to adequately equip any prospective builders.

This hack gets the job done. If it’s looks you’re after, an artistic expression of maker skills and astronomy can be seen in this planetary map that relies on persistence of vision.

Hey,

The ModuPong YouTube channel is about a modular robotics system that tracks a ping pong ball in real-time. In addition, we cover in this channel how the system predicts and responds in less than 130ms.

Please tell me if you have any ideas on how we could make our system better. Cheaper and faster would be great!