myelectrons / sfm3300-arduino Goto Github PK

I'm writing an Arduino library to use this sensor in an open source ventilator project. I have seen You just use 1 command 0x31AE to get serial number as indicated in the sensor I2C functional description document but there is another document indicating a second command (0x31AF) is needed.

As we still don't have the sensor , do you know the reason for this difference?

I'm working on a related project with this sensor in the ventilation space and running into volume accuracy issues. It seems like for low flow values, the volume is reasonably accurate (but on the order of ~ 2-3ml error over 500ml of flow).

The sensor is actually being talked to indirectly through an I2C -> FTDI converter cable. This seems to be robust, but I also suspect some error here as the USB connection adds a few milliseconds of delay.

I was wondering what your setup was for testing volume -- I suspect that my inaccuracy is due to either turbulent flows or some other sensor issue. I've been able to improve accuracy by implementing a temperature control loop.

In particular:

• You reported sub-cc accuracy in volume measurement. What volume of airflow was this error measure over? (the greater the volume, the more drift in measurement)
• What was the peak flow of this measurement? (approximate heuristics/description appreciated, even such as "gentle manual squeezing of a BVM respirator attached to the sensor" helps if nothing else is available)
• How much tube "space" was there in the setup approximately between the flow generated and the sensor?

I tried to rebuild this project with an "Arduino Nano 33 IoT". It's this device: https://store.arduino.cc/collections/iot/products/arduino-nano-33-iot

• First of all - the 5V-Pin does not deliver 5V out of the box. That took me some time to find out. You have to solder / short a jumper, see https://github.com/ostaquet/Arduino-Nano-33-IoT-Ultimate-Guide#how-to-save-power-with-the-arduino-nano-33-iot.
• The pins A4 and A5 have an internal pull up and are designed to be used as an I2C bus (https://github.com/ostaquet/Arduino-Nano-33-IoT-Ultimate-Guide#important-things-to-remember). This means you can wire the sensor direct with the board.
• Wireing is VDD -> 5V / SCK -> A5 / GND -> GND / DATA -> A4
• The connection of the sensor ist not so easy. I taped four jumper wires together an held them by hand, just as prove of concept. It worked. I also found, that someone soldered the connection, or 3D printed the thing.
• I achieved the best results with "SFM3300_Original_CRC.ino"
• My goal was to messure peak flow. For this the range of the sensor is too small. Max of my sensor was 262.50 slm. It is by far not enough. You would want something like 680, see https://en.wikipedia.org/wiki/Peak_expiratory_flow#/media/File:Normal_values_for_peak_expiratory_flow_-_EU_scale.png.

That's it. I had a lot of fun solving the problems. Thanks a lot @MyElectrons!

Hi @MyElectrons,

I am a biomedical engineering student trying to use your code to develop a class project. I have some coding experience, but have never used an Arduino before. I have a few questions regarding the initialization process that you followed to setup your Arduino.

1. What steps did you take to initialize your Arduino before you could run any of your sketches on it?
2. I'm guessing you had to follow one of Arduino's Quickstart guides to initialize the microchip you used. I was curious which guide you followed? (For example, I'll probably be using the UNO Rev3, which gives guides for Arduino IDE 2.0, Arduino IDE 1.8, and Web Editor)
3. If you used a different guide than one I listed, do you know if me using one of these stated above would still allow me to use your sketches?

Thanks for sharing your code, and I hope to hear from you soon!
-Ramon