Radiation scaler using RS232 is not working

Hello! I have a project which requires to ask radiation scaler to start counting using RS232. The radiation scaler that I use is Ludlum M2200. There are several commands (attached) that can be used to manage the radiation scaler. At first, I connected my Ludlum to PC using RS232-USB cable (https://tokopedia.link/QurWnQ8x0zb). This worked just fine along with the commands I sent to Ludlum. However when I tried to use RS232-TTL converter module (https://tokopedia.link/P6otoHpy0zb), it didn't work, even the scaler won't start counting.

This is the program I wrote:

#include <SoftwareSerial.h>
const int RX_PIN = 8;  // Pin arduino untuk receive data
const int TX_PIN = 9;  // Pin arduino untuk transmit data

SoftwareSerial RS232(RX_PIN, TX_PIN); 

void setup() {
  Serial.begin(9600);  
  RS232.begin(2400);  
  //RS232.print("SS\r\n");
} 

void loop () {
  RS232.print("SO\r\n");
  delay(4000);
} 

This is the communication that is used by Ludlum M2200

These are commands used by Ludlum M2200

This is how my wiring is:
Ludlum M2200 (female RS232) -> male to male RS232 cable -> RS232-TTL converter module (female)

From RS232-TTL converter to Arduino:
VCC -> 5V
GND -> GND
RXD -> Pin 9 Arduino
TXD -> Pin 8 Arduino

Please help me to figure out the right connection and the program

Looks like rx and tx are swapped. To avoid changing wires, just swap them in your defines at the top of your sketch.

Maybe the scaler is meant to be used with true RS232 voltage levels from a PC port and so should have +5V and -5V ( or +/- 12V) signals instead of +5V and 0V.

@herbschwarz Also possible, but as I read the text in post 1, he has rx to rx; worth testing before ordering hardware he will need to integrate.

The TTL-RS232 adapter that the OP is using should take care of that - the link says that it has a MAX3232 chip which I believe has the charge-pump circuitry to generate those sorts of voltages.

Maybe the RTS/CTS (as mentioned in the first image of the manual) is required.

Did you configure that on the PC or did it work without it?

So I shoud connect rx to rx instead?

Can you elaborate this? I believe I have connect the TXD from the RS232 module to RX pin on Arduino

Well on the PC I just use this cable while setting the port at: 2400 baud, 8 data bits, 1 stop bit, no parity, and hardware control

Can you try again on your PC and this time turn off any form of handshaking in your comms program. I think it may be something like Flow Control = None or similar wording.

I don't know, but did you try it? It's quite literally going to take less time than it took you to reply.

Willardse,
You need to connect the Arduino RX pin to the RXD pin on the RS232 to TTL converter, and Arduino TX pin to TXD on the converter.

The place where you need to connect transmit to receive, and receive to transmit is at the 9 way D-connectors.

Good point! The TTL side of the RS-232-TTL adapter has only Rx & Tx signals not the handshake signals CTS & RTS, so those are missing and there is no complete communication.

You can override/bypass the RTS & CTS hardware handshaking by connecting RTS signal to the CTS signal.

If your RS-232 cable is wired for all 9 pins of the DB-9 connector, then those handshake signals should make it through to the DB-9 connector on your RS232-TTL adapter board. You should be able to connect the RTS pin and the CTS pin together on the underside of the board using a short wire between the pins of the DB-9 connector.

That should convince the instrument that it is OK to send data.

Okay I have tried to connect my Ludlum to PC using USB and the flow control = none worked. What's next?
WhatsApp Image 2023-05-23 at 8.39.42 AM

Connecting the RTS and the CTS pin through the back of the module means this one, right?

Ok I have tried this and it still didn't work

Also from this software I used, I noticed the light of CTS and DSR have to be "ON
" so the Ludlum can make connection to PC (?). Does this mean anything? @markd833
WhatsApp Image 2023-05-23 at 8.56.53 AM

Something else to be careful of is that the RS-232 Tx and Rx lines are not crossed between the TTL-to-RS232 adapter and the Radiation scaler.

That would suggest that RTS & CTS are not used. However it could be that the PC adapter is driving CTS anyway.

Are you saying that you can turn the CTS & DSR indicators off and the Ludlum stops communicating?

Yes, that's correct.

Pins 7 & 8 on your 9-pin D-Conn in post #16 are the RTS & CTS signals. They are the middle 2 unsoldered pins on the board.

Also retry, as others have suggested, swapping over the rx & tx signals going to your Arduino. You can do that in your code, or by physically swapping the 2 wires over. The latter is obviously quicker!