I plan to use a Nano to send Time to a Vorne M1000 Serial Message Display panel over RS-232. I'm using a TTL to RS-232 conversion module between Nano and the Vorne M1000. The display does not talk back so I'm only using the Rx and Ground on the panel.
I am reading conflicting accounts of how to make the connections. Some say to join the ground from panel through converter through to Nano, which doesn't seem right to me. Still other's say to keep the ground separate. More then say the shielding in the cable gets connected to ground on the panel only and other the opposite.
I'd really like to avoid burning up the panel by connecting everything correctly. So, common ground all the way through or not? Shielding connected to ground on one end or both, which end?
Ground always must be common with single-ended signals. Not necessarily with differential signals and not at all with current-loop.
Connection through a module can be bypassed as unreliable, or can be used as a fusible in case of VERY bad conditions. I never added a bypass to a module with ground connectors at both sides.
Shields can be connected to one end only, to avoid ground loops. The shield should be grounded on the most sensitive (input) end, but as RS232 is bidirectional it's a matter of taste or stronger ground. Using shield instead of ground wire is bad practice.
@Paul_KD7HB names it: signal ground should be kept separate from frame ground (shield).
With RS-232, there is a signal ground and may or may not be a frame ground. Your module uses and needs the signal ground. Both of your end devices need the signal ground.
If the frame ground is not needed for passing power, do not connect it.
The Arduino end uses TTL signal, one side being the ground, That is your common ground.
The adapter should not have a connection between the TTL ground and the signal ground on the other side. If there is a connection, then you are good to go. All grounds will be common and no separate signal ground. Check the module with an Ohmmeter.
That schematic helps, thank you. I tested the module input and output ground and they are common.
I used the panel before with a radar gun that had an RS-232 output to display the speed of a pitched softball, so I know the panel and RS-232 port work. I tried to hook it all up last night and couldn't get the Time string to appear on the panel, but I think this is a syntax or panel settings issue.
