Read serial and extract reading

General
1

Hello
Perhaps you can help me. I am new with Node-Red.
I want to read from my serial (USB) on a Raspberry.
The incoming data are coming from a oiltank level ultrasonic sensor.
The sensor is sending every 60min data. The data are 22byte.
I am only interested in 2 bytes. In my case i need byte 16 and byte 17.
I found that i have to multiply the value of byte 16 and add the value from byte 17.
The result will be my remaining liters beeing in the oiltank.
Actual i found the Serial in node and configured it.
My Debug gives me after a few hours some data:

Raw:
[83,73,0,22,2,16,11,30,27,80,94,82,94,0,0,0,9,217,15,57,70,169,83,73,0,22,2,16,12,2,25,80,94,82,94,0,0,0,9,217,15,57,40,6,83,73,0,22,2,16,12,34,23,80,94,82,94,87,0,56,9,217,15,57,232,232,83,73,0,22,2,16,13,6,20,80,94,82,94,0,0,0,9,217,15,57,67,195,83,73,0,22,2,16,13,38,18,80,94,82,94,88,0,56,9,217,15,57,18,108,83,73,0,22,2,16,14,10]

I guess i need this part:
83,73,0,22,2,16,11,30,27,80,94,82,94,0,0,0,9,217,15,57,70,169

Now the question: How can i split and convert the values and how can i calculate with them?
The result must be 2521.
The flow will be: Serial in --> Function (With some code) ---> Text (UI) with my liters?
What will be in the function?
Thanks a lot!
Best,
Bjoern

2

Hi Bjoern, welcome to the Forum.

So, you want to extract byte 16, multiple it by 256 and add the result to byte 17.

A simple approach is to transform your buffer into an array and then do the calculation in a function node. The code in the function node will looks like below.

let arr = [];
arr.push(...msg.payload);

let result = 256 * arr[16] + arr[17];
msg.payload = result;
return msg;

Testing flow:

[{"id":"aec7271c.7e2cc8","type":"tab","label":"Buffer to Array","disabled":false,"info":""},{"id":"de279ecf.c999e","type":"inject","z":"aec7271c.7e2cc8","name":"Go","topic":"","payload":"","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":170,"y":200,"wires":[["42ed8e64.d7325"]]},{"id":"42ed8e64.d7325","type":"function","z":"aec7271c.7e2cc8","name":"Dataset Buffer","func":"msg.payload =  Buffer.from([83,73,0,22,2,16,11,30,27,80,94,82,94,0,0,0,9,217,15,57,70,169,83,73,0,22,2,16,12,2,25,80,94,82,94,0,0,0,9,217,15,57,40,6,83,73,0,22,2,16,12,34,23,80,94,82,94,87,0,56,9,217,15,57,232,232,83,73,0,22,2,16,13,6,20,80,94,82,94,0,0,0,9,217,15,57,67,195,83,73,0,22,2,16,13,38,18,80,94,82,94,88,0,56,9,217,15,57,18,108,83,73,0,22,2,16,14,10]);\nreturn msg;","outputs":1,"noerr":0,"x":340,"y":200,"wires":[["c1ecba39.570e38"]]},{"id":"3524ee2a.fdd192","type":"debug","z":"aec7271c.7e2cc8","name":"","active":true,"tosidebar":true,"console":false,"tostatus":true,"complete":"payload","targetType":"msg","x":730,"y":200,"wires":[]},{"id":"c1ecba39.570e38","type":"function","z":"aec7271c.7e2cc8","name":"Calculate result","func":"let arr = [];\narr.push(...msg.payload);\n\nlet result = 256 * arr[16] + arr[17];\nmsg.payload = result;\nreturn msg;","outputs":1,"noerr":0,"x":540,"y":200,"wires":[["3524ee2a.fdd192"]]}]
1 Like
3

Hello Andrej
Thank you very much for your answer.
I am not sure what kind of data will come from my serial. Buffer of String.
The bad thing is that my device only send every 60min. So long time to wait :frowning:
What do you think about this in my function node:

var buf = Buffer.from(msg.payload);
var one = buf.readUInt8(16);
var two = buf.readUInt8(17);


msg.payload = one * 256 + two;

return msg;

One question to the serial buffer. Will it be empty after reading? Or do i have to clear it after reading?
Thanks again.
Best, Bjoern

4

You can chose between binary buffer or string when you configure the serial in node.

r-01
r-01579Ă—631 16.1 KB

Works perfectly. Nice usage of Node.js buffer. Thumbs up !

You chose the event that will make the serial node to pass the message to the next node in the flow.

r-02
r-02574Ă—592 16.7 KB

Once the serial in sends the data its buffer is cleared.

5

Merry Christmas
Thanks for answer. Unlikely i get only errors over night.
And the most not positive point is that i deleted them...
So, my function is not working. I think that my sensor deliver the data in a different format then i mentioned
before. Can it be possible that i get HEX from sensor?
How can i convert? How i can find out what format i get?
I added a debug node to serial. But the result was that what i wrote in first post.
Perhaps the debug node has changed the kind of view?
Sorry for stupid questions but i am at the very beginning.
Thanks and best,
Bjoern

6

Hello again
Now i got again a debug node:

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 83 ]

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 73 ]

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 0 ]

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 22 ]

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 2 ]

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 16 ]

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 10 ]

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 24 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 52 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 80 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 94 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 82 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 94 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 0 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 0 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 0 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 9 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 215 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 15 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 57 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

[ 212 ]

24.12.2019, 10:14:48node: 55a73bc4.20ba9c

msg.payload : buffer[1]

[ 225 ]

It looks like real decimal values. But when i click on the small arrow in front of each value i get this:

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x53

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x49

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x0

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x16

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x2

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x10

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0xa

24.12.2019, 10:14:47node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x18

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x34

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x50

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x5e

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x52

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x5e

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x0

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x0

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x0

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x9

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0xd7

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0xf

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0x39

24.12.2019, 10:14:48node: 55a73bc4.20ba9cmsg.payload : buffer[1]

buffer[1]

0: 0xd4

24.12.2019, 10:14:48node: 55a73bc4.20ba9c

msg.payload : buffer[1]

buffer[1]0: 0xe1

Is this HEX? Do i have to convert? How can i convert?
Thanks and best regards,
Bjoern

7

As they say - they are buffers - and clicking them just shows them in different formats. so decimal 83 is the same as hex 0x53.
They are the same value so nothing to convert...

8

Hello
It is a Christmas miracle: It is working now.
The problem was the setting of the serial node.
I changed in settings the value for "Split input" to "on the character". That is wrong.
I need "after a timeout of 10000ms"
Perhaps it is a little long but it is working :slight_smile:
Thanks to all and Merry Christmas.
Bjoern

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