Issue to read serial port

General
1

I'm interfacing a Kern weight scale through serial port with Node-RED. The communication works perfectly in a terminal in both direction.
However, I'm only able to write to the serial port with NR with the "serial out" and "serial request" node but I wasn't successful to get any answer form it with either "serial in" or "serial request" nodes.

For example, when I monitor my serial device with "cat /dev/ttyUSB0" in a terminal while sending a message from NR, I get an answer in the terminal but nothing from within NR, "serial request" node goes in timeout and "serial in" remains mute ...

What am I missing ?

nodejs: 12.18.3
node red: v1.1.3
node-red-node-serialport: 0.11

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2

I am not sure whether it would give that symptom, but perhaps the sequence \r\n does not appear in the stream. Have you tried other options there, specify a timeout for example, or fixed lengths with a short count.

3

I've tried these 2 additional options to configure the "input":

  • split the input into fixed length
  • and set a timeout
    but I neither get any answer from the serial port in NR.
4

What did typed in in the terminal that worked?
Also IO as string?

Do you have a link to the manual from that scale with protocol description.

5

There is a list of command as indicated here: https://dok.kern-sohn.com/manuals/files/English/KCP-ZB-e-v1.3.7.pdf

I0 is one of these commands that lists the available commands on the device. Commands and answers are ASCII string and end with CRLF.

In a terminal with "picocom --flow n -c --omap crcrlf /dev/ttyUSB0", communication is working fine.

The "serial out" works fine, if I trigger a command with it, I can "cat" the answer from /dev/ttyUSB0 but get nothing from the "out" node.

6

Can you ensure that only one thing is trying to access the port at one time. You probably can’t share serialport with node-red and picocom st the same time. And indeed maybe even out and request nodes

7

Thanks for the hint ! That was it !
I've clean up my flow and kept only a single "request" node and killed any other process accessing the port.
After deploying and restarting the flows, it finally captures inbound data from the serial port within NR.

THANKS !

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8

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