Read Data from energy meter using Modbus RTU in Arduino Mega - arduino

Question

Trying to read data from the energy meter. The code suppose to read voltage data and return but it's some random numbers are showing. Where am I making mistake in the code? Meter is conzerv EM6436 Energy Meter.
Tried:- 1) converting data in uint16_t fail
2) Reading different other registers fail
3) The energy meter showing correct data on modscan.
Energy Meter register Link
#include<ModbusMaster.h>
#define MAX485_DE 3
#define MAX485_RE_NEG 2
ModbusMaster node;
void preTransmission() {
digitalWrite(MAX485_RE_NEG, 1);
digitalWrite(MAX485_DE, 1);
}
void postTransmission()
{
digitalWrite(MAX485_RE_NEG, 0);
digitalWrite(MAX485_DE, 0);
}
void setup() {
pinMode(MAX485_RE_NEG, OUTPUT);
pinMode(MAX485_DE, OUTPUT);
// Init in receive mode
digitalWrite(MAX485_RE_NEG, 0);
digitalWrite(MAX485_DE, 0);
Serial.begin(19200,SERIAL_8E1);
//slave ID 1
node.begin(1, Serial);
Serial.println("Starting Modbus Transaction:");
node.preTransmission(preTransmission);
node.postTransmission(postTransmission);
}
uint16_t newData = 0;
float floatData;
double dataOne;
void loop() { // loop starts from here.
static uint32_t i;
uint8_t j, result;
uint16_t data[10];
i++;
result = node.readHoldingRegisters(3036,1);
Serial.println(" ");
if (result == node.ku8MBSuccess) {
Serial.print("\nSuccess, Received data 0: ");
for (j = 0; j < 1; j++) {
data[j] = node.getResponseBuffer(j);
floatData, dataOne= node.getResponseBuffer(j);
Serial.print("\nHex data:");
Serial.print(data[j], HEX);
Serial.print(" ");
Serial.print("\nDec data:");
Serial.print(data[j], DEC);
Serial.print("\nfloat data:");
Serial.print(floatData);
}
} else {
Serial.print("Failed, Response Code: ");
Serial.print(result, HEX);
Serial.println(" ");
delay(5000);
}
delay(1000);
}
Result:-
Success, Received data 0:
-> Hex data:648F
-> Dec data:25743
-> float data:25743.00⸮

Answer 1

As Bosz suggested in the comments above, the first thing you need to do is read two Modbus registers instead of 1. So change:
result = node.readHoldingRegisters(3036,1);
to:
result = node.readHoldingRegisters(3036,2);
Then you need to work with both registers and combine them to get the float you are looking for:
if (result == node.ku8MBSuccess) {
Serial.print("\nSuccess, Received data 0: ");
for (j = 0; j < 2; j++) {
data[j] = node.getResponseBuffer(j);
}
unsigned long temp = (unsigned long)data[0] + (unsigned long)data[1]*65536;
floatData = *((float*)&temp);
Serial.print(floatData);
}
This conversion should work for any FLOAT32 values on your device's register list.
This particular problem has been discussed in several places, you can see for instance here.