Node-Red buffer

General
1

Hi, I’m new to Node-Red so I’m just working my way through all the various nodes.

I want to use Node-Red to read an Electricity meter which uses IEC 62056-21 protocol. I have the meter connected over RS232, if I use the meter software I can read it, but if I send the same serial commands using an inject node and Serial node, I don’t get a response.

I used a COM port monitor to record all the data on the TX, RX lines. So I have all the commands sent by the meter software, I need to somehow copy the TX data to Node-Red to replicate the meter software.

So, I think I need a buffer? The command I need to send to the meter is “/?! “ which is ASCII? The meter then responds with HEX data (Voltage, current, Meter Serial number...).

How do I convert this string “/?! “ In Node-Red so the meter understands the request?

2

I think that you need to check the hex values of what is being sent first.

This guide tells you how to use binary buffers with Node-RED:

http://www.steves-internet-guide.com/understanding-buffers-node-red/

As for input, you need to understand how a response is terminated. This cropped up the other day on the forum. Not all serial outputs are terminated with a line-feed. They may be of a specific length for example. Or you may need to wait for a timeperiod to know when to let the serial-in node send the data it received.

3

Hi - if it really is ascii “/?! “ then you may not need a buffer ... but you may need to add a line feed \n or carriage return \r to the end to "hit the enter key"

Or in the inject node for example you can insert a buffer

image
image918×136 2.7 KB

and if you hit the 3 dots on the right you can see it expands to show the hex
image
image980×742 17.9 KB

(and in this case see there is an extra blank space at the end.... so it may or may not really be ascii)

4

Hi everyone, I’ve got a little bit further!

I used a function node with the message:
Msg.paylaod= “/?!\r\n” and I’ve got a response! image|640x480 image image

Now I need to send a list of commands to the meter in the same function. For example
Message 1 (/?!\r\n)
Wait 1 sec
Message 2 (XXX)
Wait 1 sec
Message 3 (XXX)...

I can then log all the responses and convert it into meter data. I’ve uploaded the list of commands I need to send to the meter.

5

Assuming that the response also ends in \r\n then the default settings on the serial-in node will work fine.

Then just a matter of splitting the resulting strings (change nodes), reformatting to whatever data you need.