To do arithmetic operations on node red Serial input binary buffer data.

[vasanth dhinakaran]

msg : Object

object

payload: buffer[64]raw

[0 … 9]

0: 0x51

1: 0x39

2: 0x0

3: 0x0

4: 0x0

5: 0x2

6: 0x0

7: 0x0

8: 0x0

9: 0x0

[10 … 19]

10: 0x0

11: 0x0

12: 0x1

13: 0xa2

14: 0x0

15: 0x0

16: 0x1

17: 0xa5

18: 0x0

19: 0x0

[20 … 29]

[30 … 39]

[40 … 49]

[50 … 59]

[60 … 63]

_msgid: "607a26a3.9f85d8"

For example i want to do buffer[12]*256+buffer[13];
How can i do it? 

[Nick O'Leary]

That shows the buffer you are interested in is under msg.payload.

So the elements you mention can be referenced as msg.payload[12] and msg.payload[13] for example.

Nick

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[Vasanth Dhinakaran]

Inside a function...I tried doing the following and connected a debug 

var MSB = { payload: msg.payload[12] };

var LSB = { payload: msg.payload[13] };

var Vtg = MSB*256+LSB;

return Vtg;

I got the following:

function : (error)

"Function tried to send a message of type string"

var MSB = msg.payload[12] ;

var LSB = msg.payload[13] ;

var Vtg = MSB*256+LSB;

return Vtg;

function : (error)

"Function tried to send a message of type number"
What is the right way to do this? .Thanks for the prompt reply

[Nick O'Leary]

Functions must return message objects not raw values. Typically you'd update msg.payload with the value you want and return the message:

var MSB = msg.payload[12] ;
var LSB = msg.payload[13] ;
var Vtg = MSB*256+LSB;

msg.payload = Vtg;
return msg

To view this discussion on the web, visit https://groups.google.com/d/msgid/node-red/7020741a-1019-4e95-b7b2-b1e8258a35f8%40googlegroups.com.

[Vasanth Dhinakaran]

Thank you Nick.It worked now.