I posted here a few weeks ago and got some helpful replies which progressed my project quite a bit but now I'm stumbling again.
I have : An Arduino Nano
A TTL to RS232 Converter
A peltier effect controller (with RS232 input)
What I want to do is send serial commands from the Arduino to the peltier effect controller so that I can control it by sending new temperature set points to it.
I have the manual for the peltier effect controller which describes the format for serial messages. Using this I connected the controller to a PC using a USB to RS232 converter. On the PC I then opened a terminal program and sent the command I wanted. The peltier effect controller responded and the set point changed successfully.
I then tried connecting the Arduino using the TTL to RS232 converter and sending the exact same message but I got neither a reply or any change in set point on the controller.
To test the TTL to RS232 converter I connected the Arduino to the PC (different PC than I was programming with) using: Arduino -> TTL to RS232 -> RS232 to USB. Opening the terminal program on the PC I could see the serial commands coming in correctly so nothing was wrong with what I was sending.
I then thought that I might have a grounding problem so I disconnected the Arduino from the USB of the other PC I was using to program it and connected a separate 5V power supply and it still didn't work.
Finally, I got a scope out and compared the signal being sent out of the PC using the terminal program to the signal being sent out of the Arduino; Both look identical.
I'm now out of ideas so would be very appreciative of any of yours