I'm controlling several multiplexers from NI DO modules. The multiplexers channel select inputs, A0-A4, are 5v. The DO modules output 5v TTL. On the bench I have everything working exactly the way I want.
Real world application is going to require 500+ feet of transmission distance. I can't go into specific details, but on the receiving end I can not use 'smart' components due to extreme environment. The muxes are specially made and only complex part. The only parts I can use are passive components, RLC, diodes.
Opamps, optocouplers, etc. fail in this environment (Where the muxes are located. Where the NI equipment is I can use any technology available)
My thoughts are to use FETs, controlled by the DO's, to transmit 48v signals. Then reduce them with a voltage divider in the harsh environment, to bring it down to 5v to control the muxes.
I'm brainstorming any other ideas, or reasons why this will not work reliably? Most likely will be switching in the 10-50kHz range.
Best Answer
You could put a bipolar transistor in emitter follower configuration on each TTL output, to lower the output impedance and boost current capability. Otherwise, I would expect various telecomms line drivers to be available to suit your needs. Presumably you are using signal-return paired connections, as well as an overall 0V line and protective shield/ground.
If the environment is electromagnetically noisy then you might also want to use co-ax or shielded-pair cable to provide individual shielding as well as the line return paths; just make sure there is 100 ohms or so in series in any 0v or ground loop. Some more general EMI filtering might also be appropriate, depending on the nature of the environment.