Arduino / Genuino and the UT803

Managing this serial stuff

We showed here, that this multimeter wants power from an external source in order to be able to send data. Now we present a working arduino sketch to read and understand the sent data ...

✈ Arduino Sketch - The Code

Double click on code to select ...

/* ///////////////////////////////////////////////////////////// 
ARDUINO/Genuino (UNO) Test/Demo Sketch for UT803 Multimeter
https://www.changpuak.ch/electronics/Arduino-reads-UT803.php
Software Version 1.0, 
22.03.2017, Alexander C. Frank
//////////////////////////////////////////////////////////////*/

#include <SoftwareSerial.h>

unsigned int i = 0;
unsigned long data ;
char MValue[12] ;
float Number = 0.0 ;
float OldNumber = 0.0 ;
String Text = "";
String Unit = "";
unsigned int Resolution = 1;

SoftwareSerial mySerial(10, 11); // RX, TX (unused)

void setup() 
{
  // Open serial communications and wait for port to open:
  Serial.begin(57600);
  // set the data rate for the SoftwareSerial port
  mySerial.begin(19200);
 }

void loop() 
{ 
  if (mySerial.available()) 
  {
    data = 0x7F & mySerial.read();
    MValue[i] = data ;
    i += 1;
    if (data == 0x0A) 
    {
      i = 0 ;
      Number =  ( MValue[1] - 0x30 ) * 1000 ;
      Number += ( MValue[2] - 0x30 ) * 100 ;
      Number += ( MValue[3] - 0x30 ) * 10 ;
      Number += ( MValue[4] - 0x30 )  ;
      if (MValue[0] == 0x31 ) Number = Number * 10 ;
      if (MValue[0] == 0x32 ) Number = Number * 100 ;
      if (MValue[0] == 0x33 ) Number = Number * 1000 ;
      if (MValue[0] == 0x34 ) Number = Number * 10000 ;
      if (MValue[0] == 0x35 ) Number = Number * 100000 ;
      Unit = String(MValue[5]) + String(MValue[6]) 
      	+String(MValue[7]) +String(MValue[8]);
      
      
      // VOLTAGE DC POSITIVE
      if ( Unit == ";80:" ) 
      {
        Text = "Volt DC" ;
        Number = Number * 0.001;
        Resolution = ( MValue[0] - 0x30 ) + 1;
      }

      // VOLTAGE AC  
      if ( Unit == ";806" ) 
      {
        Text = "Volt AC" ;
        Number = Number * 0.001;
        Resolution = ( MValue[0] - 0x30 ) + 0;
      }

      // OHMS
      if ( Unit == "3802" ) 
      {
        Text = "Ohm" ;
        Number = Number * 0.1; 
        Resolution = ( MValue[0] - 0x30 ) + 1;
      }
      
      // OUTPUT ONLY IF REASONABLE VALUE
      if ((Number > 0.95 * OldNumber) && (Number < 1.05 * OldNumber)) 
      {
        Serial.print(Number,Resolution);
        Serial.print(" ");
        Serial.print(Text);
        /* Serial.print("\t\t");
        for (int j=0; j<10; j++) 
        {
           Serial.print(char(MValue[j])); 
        }
        */
        Serial.println(" ");
      }
    OldNumber = Number ;
    }
  }
  
}

// ///////////////////////////////////////////////////////////// 
// END OF FILE.
// /////////////////////////////////////////////////////////////

✈ The Bits / Bytes in detail

The UT803 uses only seven bits. That's why we masked out the 8th (MSB) in line 33.

Sometimes (when you look away) the UT803 sends garbage, or the arduino receives garbage. For that rare case we introduced some kind of check in line 77.

Under normal circumstances, there are eleven bytes sent. This may look like this :

0x30, 0x30,0x30,0x30,0x30, 0x3B,0x3C,0x30,0x3A, 0x0D,0x0A

The very first byte is a "multiplier". Multiply the following numeric value with ten to the power of this number. (e.g. 10^0 = 1, 10^1 = 10, 10^2 = 100, ...)

Bytes 1,2,3 and 4 represent the numeric value. This is a four digit number between 0000 and 5999. The decimal point is defined by the following "unit" and the multiplier (Byte 0).

Bytes 5,6,7 and 8 represent the unit. We did not test all of them, but will give some examples here. ;80: is Volts DC, ;806 is Volts AC, 3802 is Ohm, 4800 is Degrees Celsius, 9808 is Ampere DC, 6802 is Nanofarad. Feel free to explore the others by yourselves ...

The very last two bytes are always 0x0D and 0x0A. They are "Carriage Return" and "Line Feed". This will end the transmission.

✈ The Serial Plotter

Is a beautiful tool to get an impression on the dynamics of your data . Using the example above you may get a graph like this :

Monitoring the power grid voltage ...

✈ Share your thoughts

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t₁ = 6740 d

t₂ = 210 ms