I’m currently developing a small application for monitoring the power / current our solar collector is generating.
The array is connected to 3 inverters. Every inverter has a RS232 interface, transmitting one Line of information(its current status) every 10 seconds.
Since I want to do the monitoring using a device only having one serial port, I need to come up with a way to be able to read the data from all of the inverters in parallel.
I don’t need to send anything to one of the inverters!
Is it possible to just connect 3 RS232 wires in parallel to one serial port? Collisions will be pretty unlikely since every inverter is transmitting only 64Byte / 10seconds ending with a newline, so I could check for variable line lengths to detect collisions.
No, you should NOT connect 3 serial output port in parallel. If you do that you are probably going to broke the RS232 output circuitry of your inverters.
You have 3 RS232 outputs, so you need 3 RS232 input, then you can manage these 3 input the way you like: maybe you can buffer the data from each input, and reoutput the data on a single RS232 output, to be connected to your monitoring device…. but you should add some code in the data flow to differentiate the data coming from the 3 inverters.
Maybe you can use some kind of IC that do the job for you, I’m not sure, but maybe that some IC that multiplex multiple RS232 input on a single RS232 output already exist.
Try this search: rs232 port input multiplexer on Google
Or, if the monitoring device is a Window computer, you can use 3 serial-to-usb converter: that will create 3 virtual COM port on your computer and you can read data from them with any software.
Update
About the hypothesis of securing the output circuitry using diods to block reentering current, I don’t think it’s going to work…
Many year have passed by since last time I’ve used an RS232 link at low level (so maybe I’m wrong) but I think that there is some kind of handshake going on between RS232 input and output port (speed to use, parity, stop bit…).
Each RS232 port have inputs and outputs signal, both for data and for transmission control, so your multiple RS232 outputs does have some input signals, and your single RS232 input does have some outputs.
This mean that your input monitoring RS323 port is going to try to make a handshake with 3 RS323 ports at the same time… and the 3 RS232 ports are probably going to respond at the same time… so I think it’s not going to work.
Other than that if you place diodes on your output, you are going to loose 0.7v, I don’t remember the tolerance on signal level of RS232, but maybe that 0.7v can be relevant.