Using Two Sensors on One RS232 Port (Alternating Power?)

Dev Kit Support
1

Hey everyone,

I’m working on integrating two sensors into a Bristlemouth Dev Kit, but I only have one RS232 port available. I understand RS232 is a point-to-point protocol and not meant for multiple devices on the same bus, but I’m wondering if this approach could work:

  • Sensors I’m using:
    • Mini CO₂ Pro sensor (4-pin RS232)
    • ANB pH sensor (6-pin, supports both RS232 and RS485—but I’m using RS232 for now)

The pH sensor seems to require all six pins connected to work properly, and the CO₂ sensor is just standard RS232.

Here’s my idea:

  • Connect both sensors’ RS232 TX/RX lines in parallel to the Dev Kit’s RS232 port.
  • Only power one sensor at a time, leaving the other completely off (so its TX line isn’t active).
  • Alternate them on a 5-minute sampling cycle. So CO₂ runs for 5 minutes, then powers off, and the pH sensor powers on for the next 5 minutes.
  • I can extend the sampling window from 10 to 13 minutes if I need to account for warm-up time between transitions.

Questions:

  • Is this “one-powered-sensor-at-a-time” approach safe or viable for RS232?
  • Could having both TX lines connected (even if one sensor is off) cause bus contention, reflections, or other issues?
  • Is there a better way to handle this if I don’t have hardware support for a second RS232 port?

Any insight would be super helpful. I don’t have deep experience with RS232 at the electrical level, so I’m trying to avoid causing issues by wiring things incorrectly.

Thanks!

2

In case someone would like to do something similar.

Not going too much into the details I think it may be possible to have two RS232 devices connected in parallel and power one of them at a time assuming that both of them have high input impedance on the transmitter’s output when they are turned off, but that may be bit of a stretch.

I think I would try to multiplex UART TX/RX lines before two RS232 transceivers.