Excel VBA send string to com port

Question

0.00/5 (No votes)

See more:

Hi From Excel VBA (Office365 on Win 10) I am trying to send a string to my new USB relay. It requires a Hex string "FF 01 01" to put the relay On, but it does not go On.

I use the VBA code, which I have copied from "somewhere".

I have also tried to end the string with Chr(13), no effect.

It opens and closes the port correct (it seems), but it does not turn the relay on.
When I use a small program (DockLight ver. 2.3) to send the Hex string "FF 01 01" it works perfect, the relay goes On.

What am I doing wrong in VBA?

Best regards
Finn

What I have tried:

Sub SendHexToCom()
COMPort = FreeFile (I dont know what this does)
Close #COMPort
Open "COM8:9600,N,8,1" For Binary Access Read Write As #COMPort
VarString$ = "FF 01 01"

Put #COMPort, , VarString$
Close #COMPort
End Sub

Posted 26-Nov-21 2:59am

Member 15445727

Updated 27-Nov-21 5:14am

Add a Solution

3 solutions

Add a Solution

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Richard MacCutchan · Answer 1 · 2021-11-26T03:10:00

VarString$ = "FF 01 01"

That is what you are doing wrong. You are sending the ASCCI character string FF<space>01<space>01 instead of the actual hex (i.e. 8-bit) bytes FF0101. You need to use the VBA HEX function to get the correct values, something like:

VB

Put #COMPort, , HEX(255) # FF Put #COMPort, , HEX(1) # 01 Put #COMPort, , HEX(1)

[edit]
I think I may have misread the documentation, you can send the hex characters directly by:

VB

Put #COMPort, , &HFF
Put #COMPort, , &H01
Put #COMPort, , &H01

[/edit]

And as an aside, if you don't understand some code that you download from "somewhere", then be aware that it could do all sorts of damage to your system.

Dave Kreskowiak · Answer 2 · 2021-11-26T05:38:00

The port may open, but are the parameters you specified the ones your device is expecting?

You opened the port with a baud rate of 9600 bps, no parity, 8 bits, 1 stop bit. You're going to have to consult the documentation on your device to see what parameters it's expecting. Get any of those parameters wrong and your communication won't work.

Member 15445727 · Answer 3 · 2021-11-27T05:14:00

Solution 3

Thank you, Dave
The documentation says 9600 bps, no parity, 8 bits, 1 stop bit.
And command to activate relay is Hex FF 01 01.

I really dont know what to do else.

Posted 27-Nov-21 5:14am

Member 15445727

Comments

Richard MacCutchan 27-Nov-21 11:53am

This is not a solution. If you want to reply to a posted solution then use the Have a Question or Comment? link below the posted message.

Member 15445727 28-Nov-21 3:52am

Thank you, Richard
Sorry for the disaster :-)

Excel VBA send string to com port

3 solutions

Solution 1

Solution 2

Solution 3

Add your solution here

Preview 0

Excel VBA send string to com port

3 solutions

Solution 1

Solution 2

Solution 3

Add your solution here

Preview 0

Existing Members

...or Join us