DP Ventilator

Website online
www.uni-flex.be

The Nextion HMI screens, everybody know them, excellent hmi interface with all the graphical source on the display side, so less resources on the arduino side. But one of the biggest problems, a decent communication in bought directions.

I did a whole research finding a decent communication but didn't find it, I wanted a simple communication without any of the libraries from Nextion.

Continuously writte data to the screen and getting data from the screen, easy expandable.

 #define NXTSerial Serial2          // Serial port to connect with Nextion panel

 Set serial port to use with the arduino board

  void NxtOpenSerial()
  {
   //This is for serial Nextion display.
   NXTSerial.begin(19200);
  }

To open the serial communication with the HMI display.

 void InitNxtData(String dev, String data)
  {
    memset(NxtMsg, 0, sizeof NxtMsg);  
    sprintf(NxtMsg, "%s=%s%c%c%c", dev.c_str(),data.c_str(),0xff,0xff,0xff);
  }

 To add data to write something to the screen (first data)

  void Add_NxtData(String dev, String data)
  {
    sprintf(NxtMsg, "%s%s=%s%c%c%c", NxtMsg,dev.c_str(),data.c_str(),0xff,0xff,0xff);
  }

Add next data as long as needed (to repeat).

  void SendNxtData()
  {
    NXTSerial.print(NxtMsg);
  }

Send all the data.

To write to the HMI dispay, use it this way;

  void Nxt_Write()
  {
    InitNxtData("P1.val",NxtMessage);
    Add_NxtData("P2.val",NxtMessage);
    ...
    Add_NxtData("P3.val",NxtMessage);      
    Add_NxtData("P4.val",NxtMessage);      
    Add_NxtData("P5.val",NxtMessage);
    Add_NxtData("P6.val",NxtMessage);     
    ...
    SendNxtData();
 }

Example: Write 6 parameters to the Nextion screen.

repeat this routine on every 50ms and send only data when it changes to shorten your data transfer.
Because you send just one line of data it stays very responsive.

    if (old_P1!=P1) {
    sprintf(NxtMessage, "%u", P1);
    Add_NxtData("P1.val",NxtMessage);      
    old_P1 = P1;
    }

 This way you only add the data when there was a change in data.

On the other hand we wanted to read data from the nextion screen.

 void Nxt_Poll()
  {
    // READE DATA FROM PANEL
    delayMicroseconds(10); // 10 usec delay 
    if (NXTSerial.available())
     {
         byte inc;
        inc = (char)NXTSerial.read();
        if ((inc >= 0xF0 && inc <= 0xFE) && !NxtSetStart) // <START MESSAGE>
          {
            NxtBufCnt = 0;
            NxtSetStart=true;
          }
        if(NxtSetStart)
          {
            NxtBuf[NxtBufCnt++] = inc;
            if (inc == 0x0A) // <END MESSAGE>
              {
                NxtSetStart=false;  
                ... 

Listen to the port if data is available, if so read char start message between (0xF0>0xFE)
If found read and store next character until character 0x0A has been read. This is the end of the message.
As you can see it is a very simple communication but it works very good.

Now lets check some data and do something with it.

                CheckNxtHex(0xF0,NXTparam);       // Read parameter data from 0xF0  
                
                CheckNxtHex(0xF1,NXTstart);       // Read parameter data fron 0xF1 and do something 
                if (NXTstart==1 && !NXTstartFlag)  {ee.active=!ee.active;NXTstartFlag=true;} // Toggle button (start/stop)
                if (NXTstart==0)                   {NXTstartFlag=false;} 

 and close communication

                NxtBufCnt = 0;

             }
          }      
      }
    else
      {
        // WRITE DATA TO PANEL
        Nxt_Write();
      }
  }

 I hope this explains a litle how I made a good  and fast working  communication with the nextion display.

To move controlled in both directions Up and Down we used springs, this way we are fully guiding the press system on the amu-bag.

We take the cover of the box and made some things on it.

Every piece has been made to easily be removable. The motor Knob can be used when the machine is powered off to clamping the abu-bag between the two squeezers.

The spring system can be easily removed

The mechanical table exists out of a strap belt, the whole mechanics has to be build into the enclosure on a easy way to get removed or inserted.

Th

It's been build around a very strong stepper motor Nema 34 with 4.5Nm torck. The driver must be very silent so we needed to work in micro steps with enough power. After several tests with different motors this was the best result. It also needed to be double shafted because we wanted to work with a motor that we manually wanted to move to bring in the ambu-bag.
The standard strap belt we used has a width of 20 mm and the thickness about 1 mm. You can find it in your local warehouse. Take the nylon one and if you cut it always use a burner to melt the ends.

 Here you see how it is brought into the enclosure.

It is very compact and fits perfectly!

This was one of my first questions, how I going to build it? Everything started with this enclosure.

This must make place for the electronics

The first 3D printed pieces where the front with its electronic components.

And this is the result