Yea, sorry, I am far from being an electrical engineer, so as far as writing up a schematic, I'd be lost. I'll try to break everything down the best I can.
Under normal operating conditions, I have a tool that creates controlled pressure spikes in closed flow loop. My pressure transducer is rated to 10,000psi and under normal conditions can see as much as 6,500psi. The transducer is very sensitive in that when connected to the receiver, I can see as little as 1-2psi fluctuations. What I assume is that the transducer contains a resistor of sorts that will vary incoming voltage from the receiver (24.15, I know because I metered it). More pressure, more resistance. Right now the tool is in the flow loop around 3,600psi and I am seeing around 55psi variances when the tool "pulses".
We currently have a small module that plugs into the same cable the transducer does, and it simulates these "pulses" while outside the flow loop. The module reads voltages from the tool (5v on line 7 means tool in in talk mode, and a "pulse" is indicated by every time line 6 jumps from 0v to 5v), and voltages change in a very static way, not dynamic as it would be when plugged into the transducer which could read anything from 0-10,000psi. Here, voltage from the receiver (24.15v) drops to 21.27 (or close), just as it does when the transducer is plugged in. Again, I know this because I metered it. When the module sees 5v on line 7, it drops the 21.27v to 20.6v. When the receiver sees 20.6v it interoperates this as a few thousand psi and starts listening for "pulses". When the module sees the 5v pulses on line 6, it in turn drops the 20.6v to 20.45v which the receiver sees as 1 or 2 hundred psi spikes.
Think of line V on receiver as Vcc and line S as Gnd. Line V sends 24.15v out and obviously, without a transducer or test module plugged in, the circuit is open. When either is plugged in, a little resistance is added to the line which drops 24.15v to 21.27v, but the circuit is now closed and the receiver recognizes this. Apparently, the receiver is calibrated to see 21.27v as 0psi, or thereabouts. As voltage drops coming back to the receiver, it sees it as higher pressure. That is pretty much the breakdown of what is happening with everything talking to each other.
I know I can't run 20v into an Arduino. What I'm thinking I could do is use incoming events to trigger the Arduino to send voltage to a board that does have this higher voltage coming into it.
Ideally, there would be an IC or something that would allow me to do something like...
Pin 1 = V in (24.15v)
Pin 2 = Looks for 5v signal from Arduino
Pin 3 = Looks for 5v signal from Arduino
Pin 4 = V out (Pass through, no Arduino events, 24.15v goes out)
Pin 5 = V out (If signal on Pin 2, 24.15v goes out here instead of Pin 4)
Pin 6 = V out (If signal on Pin 3, 24.15v goes out here instead of Pin 5)
From there, I can apply resistance to the paths as need. The Arduino just triggers detours in the current.