Hi,
I'll try to give a bit of explanation, but it will probably be incomplete....
This topic is one where, if you understand TTL electronics, the schematic in the manual will be pretty obvious (in which case you don't need to be given a schematic to follow). If you don't speak TTL logic, the schematic is not of much help....
I kind of knew when I included the schematic that I was in a damned if I do, damned if I don't situation...
Here are the core concepts:
Most BoBs have a resister on the board to pull an unused input high. This prevents floating inputs from being triggered by noise etc.
If you connect a normally open switch from the BoB input to gnd, you have created an "active low input" sensor.
Push the switch, the input line is shorted to ground, mach sees the input go active (active low). Release the switch, the resister pulls the input back high and mach see the input go inactive (it's high and the input is "active low").
If you connect 2 or three switches **in parallel*** to the input, any one of the switches will create the active low input signal to mach.
In electronics land this is called "wried-or'ing" inputs. The name comes from boolean logic: the input state = Switch 1 OR switch 2 OR .... switch N closed.
A little thinking about this will hopefully result in understanding why this only works for active low input devices in parallel. Think about what happens if the switches were normally closed instead of normally open...
This also does not work for combination of active high and active low devices. To make a combination work as desired, what's needed to get touch plates and probes all on the same input pin. The different devices have to converted to all present active low TTL signals to the input pin. The schematic in the manual shows a way to take one acitive high device (a typical probe) and two active low devices (the touch plates) and connect all three to the probe input pin (the schematic is for a Bob that uses TTL input voltage levels).
Hopefully, this helps. If not, the choices are to
1) start learning more about TTL electronics (before doing somethign that "let's the magic smoke out" of your BoB or other electronics, or
2) Find someone that knows enough electronics to build you an interface card (pehaps similar to the schematic in the manual), or
3) call your favorite BoB vendor and tell them there is a market opportunity if they include this feature in a BoB...
Dave