RS232 doesn't work with certain device

If no hardware handshake is used, RTS and CTS should not be relevant at all. But the mixer might look for the DTR signal to check if a controlling device is connected.

Maybe it's time that you show us the whole wiring of your project as you have it currently. Is it possible that you take a photo or draw a wiring diagram?

These are some photos from the wiring. Nothing special, just TX/RX to the TTL to RS232 board and 5V to it. Then the fader is 3.3V power/ground and the other wire to A0 input. Hmm, I just see that the shadow doesn't let you see anything. The blue wire is connected to TX and white to RX

How can I use the RTS and CTS port? Should I just connect it with a digital port and send High? Or how does it works. It's plausible that the video mixer sees if a device is connected with the RTS/CTS. Or should I connect certain pins from the connector?

Thanks for the help! I'm a really newbie in serial/RS232/arduino/IC stuff :)

I am a little puzzled, to say the least, that you don't seem to have anything connected to the output of the RS232 board. How does that work?

The output of the RS232 board is connected with a standard RS232 cable to the video mixer.

The TTL to RS232 is connected to the arduino with the blue/white cable to TX/RX.

Is it possible to connect a digital port from the arduino to the CTS (clear to send) from the TTL to RS232 port? And just write high to this port so the MAX2323 sends over RS232 that there is a device connected.

Just tie it high (or low as appropriate) - you don't need to write to a pin to do that.

Check the specification of the remote end RS232 (peripheral). RS232 comes in flavours... The original RS232 standard asks for a Voltage swing between +15 V and -15V. but used to work fine with +/- 12V. The chip (MAX3232) on the RS232 converter however provides + and - 5.5V max which is generated using charge pumps.... these pumps have limited power (drive) capabilities. All be it that this works fine for most devices it would not work for devices which accept only signals in line with the original specification.

Also, do not use long flat cables to interconnect (>1m). The relative high capacitive load of these cables will have a negative impact on the integrity of the electrical signals.

Boosting the signal level for TX sometimes resolves the issues and is not hard. You need a dual power supply of +/-12 V i.e. 24V between the "0" and "1" state. 2 switching transistors and a few resistors would "boost" the signal. Note: with additional components, a distorted signal (long cables etc.) may be overcome too. do not omit the reference ground...

You typically only need boosting the TX (transmit from the converter to the receive of the remote device), the transmit of the (old skool rs232) peripheral typically provides more than enough power to the input of the Max3232/arduino.