I'm hoping you guys might be able to give me some advice on the best approach for this project. The bare bones of the problem is that I have multiple identical RS-232 sensors that I am looking to communicate with using an Arduino and appropriate transceiver chip(s).
My initial thought was to utilize multidrop RS-485 with 485-to-232 converters at each sensor. However, I cannot modify the sensor code and, if my understanding is correct, I would need to use addressable 485-to-232 converters such that only one sensor would respond each time I sent out a request for data. Since all the sensors respond to the exact same request, is my assumption correct that non-addressable converters would send the command through to every sensor simultaneously and result in a massive mess? If so, do you know of any reliable, reasonably-priced addressable converters - where reasonably priced means cheaper than building my own addressable converter from an Arduino to use at every node?
As an alternative, I came up with the idea of sticking with 232 and having a way of selecting a specific sensor to communicate with at a time. For cost and ease of manual assembly, I am looking to stay with a 328 chip, so I am limited to a single TTL serial port (software ports do not begin listening to the receive line soon enough and miss data). My thought is to use transistors (or some other switching means) to switch either the TTL connections between multiple transceiver chips or switch the output of a single transceiver between a number of 232 lines using additional pins on the arduino (a la SS pins in SPI) and biasing any disconnected transmit lines to their neutral state. Data is only sent towards the arduino after a request, so I do not have to worry about loosing information when a given line is not requested. Is this a good idea/possible/crazy?
Thanks!
-Scott