Super simple low cost ZERO SOFTWARE ventilator controller - Page 1
Forum section: electronics / projects

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 14, 2020, 12:11:37 am
content: I thought I'd post a fun circuit for people to play with - it was inspired by the University of Florida Open Source Emergency Ventilator project. But really it's just an adaptation of a handy 555-driven low power timer pulser circuit for AC or DC loads.This could be used on other sorts of emergency ventilator designs - could be a piston-actuateg bag squeezer, peristaltic pumper, blower or some other breathing aid device. Could also be a roadside light flasher, Halloween decoration, or whatever you want.This is only meant to be an example schematic and learning tool- users can develop their own modifications and Bill of Materials to suit whatever parts are available and whatever need they have.Sometimes in this age of cell phone apps people forget how simple a timer circuit can be...I'm not against using CPU's and MCU's in all sorts of systems - I make my living doing that at all levels. BUT SOMETIMES software just isn't required - and in the case of a product that needs emergency FDA clearance for cybersecurity, it's really handy to kick out an old school quickie 555 circuit. Just eliminate the software hacking problem altogether. Don't even need a PC board made either.I know some readers might not be completely familiar with 555 timer circuits, or how to adjust the duty cycle of a timer with a simple comparator, or how to easily control a low power AC load with a small SSR chip. Here you go... Here's a super simple, super reliable and inexpensive way to help save someone's life - or make a cool gadget for a science fair or Halloween prop.Link to a Google drive with example open source schematic, complete circuit description, oscilloscope shots taken during testing and an exciting demo movie.https://drive.google.com/drive/folders/1wJ81SEzPLlEspD-UX3PU1LFRpdiZRutf?usp=sharingLink to Open Source Ventilator project:https://simulation.health.ufl.edu/technology-development/open-source-ventilator-project/AGAIN: This is only an example that was built and validated based on parts we had in stock, and looking around at parts distributors to see what was in plentiful supply that's inexpensive. There are a million ways to do this circuit; this is ONLY an example.Another note: Already I've been asked "Why not use a zero-crossing TRIAC chip to control the AC coil"? Because this circuit is designed to drive low power AC loads at 24VAC - namely a low power sprinkler valve with AC control coil. The zero crosser won't even work correctly at low AC voltages, and it's really not desired anyway for this use.Have fun!

author: drussell
author_rank: Super Contributor
timestamp: April 14, 2020, 12:27:57 am
content: timer≠ventilator controller

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 14, 2020, 12:39:02 am
content: Quote from: drussell on April 14, 2020, 12:27:57 amPlease see the University of Florida project. It's an EMERGENCY ventilator design. Nobody (even project managers) claimed its a good device, it's just something that can be cobbled together if required without waiting months for manufacturers to catch up. It just needs the valve to operated in atimed fashion- as are just about all of the open source emergency designs.If you're drowning and have a chance to be attached to a real ventilator, use that. If it comes down to a last ditch effort to keep you breathing with a sprinkler valve, some PVC parts and a good luck 555 timer - well that's where this circuit comes in. Maybe this is all that's available to someone in certain parts of the world.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: April 14, 2020, 12:39:27 am
content: Welcome back MisterDiodes !

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: April 14, 2020, 01:02:21 am
content: Quote from: drussell on April 14, 2020, 12:27:57 amIf you had taken the time to actually read and understand the project first before commenting, you would have seen that it actually works, it's simple and reliable and would work in a pinch until the real thing was available, that is all it is. A ventilator doesn't have to have a CPU and a hundred bells and whistles to work, check out the older models that didn't have CPUs or even electronics, just a mechanical machine to do the work and that likely wasn't as reliable as this circuit and cost a lot more.....so where's the beef?

author: wraper
author_rank: Unknown
timestamp: April 14, 2020, 01:13:17 am
content: Quote from: Edwin G. Pettis on April 14, 2020, 01:02:21 amI've read it and completely agree withdrussell. Timer is not a ventilator controller. I guess it's trendy to talk "ventilator" about just anything. Medical ventilator is about supplying particular pressure to lungs, not turning air pump on/off.

author: wraper
author_rank: Unknown
timestamp: April 14, 2020, 01:18:15 am
content: Quote from: MisterDiodes on April 14, 2020, 12:39:02 amLooking into attached documents it's about how to kill patient very painfully by forced ventilation of lungs. It's not how medical ventilator works. Real ventilators either supply pressure above ambient to ease lung operation or if pressure is modulated, they sync it with lung operation, not force air into lungs. What you posted here is a torture device if used as ventilator controller.

author: floobydust
author_rank: Super Contributor
timestamp: April 14, 2020, 01:21:14 am
content: It would be fine with a ventilator bag as you can't overfill the lungs and damage them, but a bit dangerous with pumps. Older, simple ventilator designs used mechanical pressure relief valves and regulators, and lots of solenoids.Ideally it would have a supervisor portion that looks at pressure and the pressure pulse to detect an open mask or hose; another op-amp and pressure transducer. These are used:Amphenol NovaSensor NPA Series Surface-Mount Pressure SensorsMany cutesy 3D designs for ventilators are here:https://grabcad.com/library

author: drussell
author_rank: Super Contributor
timestamp: April 14, 2020, 01:41:20 am
content: The basics are reasonably well covered in this video:

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 14, 2020, 03:46:59 am
content: DRussel - I think you need to reconsider just a little. I 100% agree - if you could put flow controller and solenoid valves and pressure sensors and ran the thing on a Core-i7 PLC that would be great. I know that.The problem is - in the spirit of an emergency device youcan't use up parts that are used in any real ventilator. Want a pressure sensor to sense the actual pressure on inhalation? Great!! Except: Good luck finding any medically approved sensors right now - for instance the popular medical breather range 0 - 0.58psi (0-40cm H2O) sensors are pretty hard to get right now, even if you wanted one. They are generally already bought and vendors like Honeywell / NXP etc. are months behind, busy filling orders for the big players. Waiting months might not be an option for some remote communities.The University of Florida project can be built with simple mechanical means for max pressure and PEEP (Positive End Expiratory Pressure). For instance PEEP can be controlled with nothing more than an airway-connected tube inserted in a bucket of water - with the end of the tube at the desired cm distance pressure below the surface of the water, and the patient exhales against that steady pressure that is enough to create bubble flow at the bottom of the pipe. A second tube is set 40cm below the water surface, and that's the overall system safety pressure. An anti-asphyxiation valve is nothing more than a ping-pong ball trapped in a pipe so that as long as positive pressure applied from the system it seals. If the system inline pressure fails and the patient inhales, the ball lifts off the seal and allows normal airflow - you never want a vacuum in the patient lines. And so on. Don't think solenoids and lots of complex valving - Think about how to do it with what is available.Low pressure bardon tube gauges (round dial) can be used as long as they are available - and in absence of that you switch over to a U-shaped clear tube stapled to the wall filled with an appropriate amount of colored water with a measuring tape stuck along side. There's your very accurate manometer tube gauge.Does the patient need warm humidifed air? That's easily done with a common CPAP style water tank and heated airway tube (Lots in supply for CPAP machines) - in a pinch a resistive warmer in the airline can be added along with an airstone bubbler along the route. Even a repurposed aquarium pump and airstone can work.In all cases what closes the feedback loop on a timer-controlled emergency ventilator is the attending nurse keeping an eye on the patient at all times.Is it ideal? Of course not.But in the spirit of an emergency, remember that something like University of Florida project will be FDA approved ONLY IF there areno real ventilators available.If you don't want to call it a "Ventilator" controller, that's fine. The schematic specifically says it isn't for medical use - because I had you in mind <Laughing>. Just call it a low power timer/ pulser for AC loads. I simply repurposed an existing circuit and applied proper resistor values to make a way to power a valve on and off, and that valve happened mounted on some PVC pipe and a bucket of water contraption that is saving someone's life.Let's hope none of us ever has to use it!!In the meantime enjoy the circuit as a fun way to teach someone about how 555 timers and comparators work. Make a Halloween decoration. Make a flashing light for your driveway. Put a heavy relay on it and cycle that million volt Tesla coil in the front yard. That would be cool!HEY- You can even modify the circuit to use a 556 timer. That way if you can mount a simple breath sensor switch on the inhalation line and use the second timer as a classic missing pulse detector to trigger an alarm!Lots of ways to do it for sure. Not one right way.If any open-source ventilator saves a life in a situation where a real ventilator wasn't available - well then it's a great design, right? By whatever name you call it.