RS232: Sending ASCII Control Strings

Projects Networking, Protocols, and Devices
1

I am unsuccessfully trying to send fixed length ascii strings through an Arduino-Uno/RS232-Shield to an emmLabs PRE2 preamp for remote volume control.

Sample String:- *PRVL20NA

I think the problem is that Arduino sends through serial only as individual bytes which are separated by a second control item:- the preamp cannot deal with this structure.

(I am somewhat new to programming!!!!)
Would anyone have a solution?

I can successfully send manually entered control strings through my PC's USB RS232 interface and Realterm terminal program.

A diagnostic capture of the RS232 shows the string sent successfully as one sequential block.
0242.428 Ascii taWaitFrSpc 00000000
0242.428 Ascii taSendBlock 00000000
0242.428 Dispatch WriteCom 00000001 *
0242.428 Dispatch WriteCom 00000001 P
0242.428 Dispatch WriteCom 00000001 R
0242.428 Dispatch WriteCom 00000001 V
0242.428 Dispatch WriteCom 00000001 L
0242.428 Dispatch WriteCom 00000001 2
0242.428 Dispatch WriteCom 00000001 0
0242.428 Dispatch WriteCom 00000001 N
0242.428 Dispatch WriteCom 00000001 A
0242.428 Dispatch WriteCom 00000001 [0D]
0242.428 Dispatch WriteCom 00000001 [0A]

I have no success when connecting the Arduino - RS232 and the preamp and sending strings through code.

A diagnostic capture of the RS232 shows the string sent as individuals.
1297.840 Dispatch ReadCom 00000001 *
1297.840 Trigger Avail 00000001
1297.841 TrDatChg Timer 00000040 [01][00][00][00]
1297.841 Dispatch ReadCom 00000001 P
1297.841 Trigger Avail 00000001
1297.842 Dispatch ReadCom 00000001 R
1297.842 Trigger Avail 00000001
1297.843 Dispatch ReadCom 00000001 V
1297.843 Trigger Avail 00000001
1297.845 Dispatch ReadCom 00000001 L
1297.845 Trigger Avail 00000001
1297.846 Dispatch ReadCom 00000001 2
1297.846 Trigger Avail 00000001
1297.847 Dispatch ReadCom 00000001 0
1297.847 Trigger Avail 00000001
1297.848 Dispatch ReadCom 00000001 N
1297.848 Trigger Avail 00000001
1297.849 Dispatch ReadCom 00000001 A
1297.849 Trigger Avail 00000001
1297.850 Dispatch ReadCom 00000001 [0D]
1297.850 Trigger Avail 00000001
1297.866 Dispatch ReadCom 00000001 [0A]

Code used below:

/*
RS232 Volume Control Reciever -
Sending two volume control codes as ASCII strings
*/
void setup()
{
Serial.begin(9600,SERIAL_8N1 );
}

void loop()
{
serial.print("*PRVL20NA\r\n");
delay(1000);

serial.print("*PRVL50NA\r\n");
delay(1000);
}

2

Is there meant to be any form of flow control on the interface?

I think the problem is that Arduino sends through serial only as individual bytes which are separated by a second control item

Serial is sent as individual bytes, yes, but what do you mean by "second control item"?

Do you have a link to a manual for the target device?

If you're going to post code, please:

  1. Use code tags
  2. Make sure it's your actual code, not just something you made up when you typed it into your post.
3

Thanks for the reply.
Full description of RS232 interface is in pages 19 - 25 http://www.emmlabs.com/pdf/manuals/PRE2_Manual.pdf
I have attached the relevant pages to this reply.
It is likely I need to manage flow control, however I lack the knowledge to implement this.

Regarding "second control item":
My unsuccessful attempt at sending code shows in my diagnostic capture the sequences of Dispatch line followed by Trigger line.
1297.841 Dispatch ReadCom 00000001 P
1297.841 Trigger Avail 00000001
1297.842 Dispatch ReadCom 00000001 R

My successful attempt at sending code direct through my PC shows the sequence "Despatch" for the total string.
242.428 Dispatch WriteCom 00000001 P
0242.428 Dispatch WriteCom 00000001 R

I look forwards to successfully send even one string to the preamp.

PRE2_Manual_RS232.pdf (545 KB)

4

How are you doing the serial level conversion/inversion?

Edit: sorry, it's there in the first post - do you have a link to the actual device, please?

What are you using to analyse the serial line?

5

Serial level conversion/inversion.
Perhaps this is the missing link?
I am using the DFRobot rs232 shield.

I have attempted using the SoftwareSerial library. In all cases I can send the ascii string to the Serial Monitor window in the Arduino program. It also displays correctly in my terminal program when I connect my PC RS232 interface to the Arduino running my sketch.

6

I am using Realterm Serial Terminal to analyse the terminal line.
Perhaps I should be looking at Raspberry PI which I understand has send/receive buffers.

Getting late this side of the world. Will be back in about 8hrs

7

I might be inclined to try using two stop bits, or spacing the individual characters sent by a couple of hundred microseconds.

When you say you used a terminal, was that typing and sending one character at a time, or sending a whole command in a single continuous transmission?

The Arduino has both transmit and receive serial buffers.

8

In the terminal software I can send the complete string as one entry by entering it in the dialogue field and pressing sendASCII

I will try your suggestions tomorrow. Thanks

9

No success with "two stop bits" and "couple of hundred microseconds".

I have found that the volume control on the preamp sends volume codes out through the amps rs232 port. I can read them through my PC terminal serial connection.

I think I need to spend a day or two attempting to read the preamps port through Arduino.

10

Solution found.

I am now able to send to the preamp ascii codes which change its operation.

Null modem connection between the Arduino shield and the preamp is required.

I finally decided to to scope the input-output of the amps rs232 and also confirm the arduino shields pinouts.

--------It was obvious that the rx and tx required crossing over.--------

I've checked the preamps documentation. It wasn't stated or obvious in the manual diagrams.

Thanks everyone for the advice.