Switch between two digital signals with no microcontroller

When I have a design problem like this, I first think "how would I decode this by hand" and then I try to implement my thought process through use of electronics.

So, when I look at your two diagrams I see only one thing that my brain can use to determine what is data and what is noise, that is the width of the pulse. The problem with passive components in a situation like this is that for one you have a square wave that will have harmonics much higher then the cut off point for your filter. This will result in a not so square wave.

The easiest way to do this will probably be in software. You can still use interrupts, but it will take a bit more work. Essentially what you will have to interrupt on an edge, and then count time until the next edge. If the length of time is long enough then you can call it a logic 1 otherwise you can consider it noise on top of a logic 0.

If you must go with passive components you might want to consider a low pass filter followed by a comparator. You would have to play with the low pass filter to get it just right, but essentially you would aim to have the capacitor charge just high enough to cause the comparator to switch its output when the bit has been on long enough. What makes this difficult is that your "glitches" are very similar to your data and it is difficult to tune your circuit just right to get your data with no glitches. Even if you are able to perfect it on paper your components wont be very precise either. It is because of this that you should seriously consider doing this digitally.

The MAX913 has a fairly high input bias current (8uA maximum) so it won't tolerate too much series resistance in the input before you start to see significant errors. Even 1000 ohms can cause more than 5mV offset.

A series resistor of maybe 500 ohms and back-to-back (inverse parallel) Schottky diodes (eg. 1N5817) across the input may work for you. Presumably the signal from the wire is less than a couple hundred mV (if not you'll be exceeding the input CM range of the comparator and also you'd get some damping of the wire with this configuration). Add another 100 ohms from the diodes to the input if you feel paranoid. Also a matching resistance of about 500 or 600 ohms respectively from the inverting input to ground to match off the offsets due to bias current.

Edit: We also need to consider the resistance of the wire, so the resistance should be 510 + 100 + 200 ohms in this case, or 810 ohms.

The input bias current of the comparator can be as much as 8uA from each input, but the difference between the two currents is tightly matched.. only 300nA at room temperature typical and 1uA worst case over temperature. That means that if we match the resistance, the offset due to the bias current will only be 0.24mV typical and 0.8mV maximum worst case. Since the comparator itself has an offset of 0.1mV typical and 3mV maximum worst case, it doesn't change things much.

Eg:-

^{simulate this circuit – Schematic created using CircuitLab}