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what i believe you mean by "resistors and crud" to get "it to come in at 5v" is a home made pull-up bank. for all you out there who don't know what this is, i am just clarifying. for all you who do, excuse the "little words".
heres how i think they did it:
the digital switches on the optical sensors are either float or ground, so to connect it into and input that is expecting 0-100k ohms, what you have to do is simulate that. so, you take a 100k ohm resistor and connect it to 5v+ on one side and the NO (black) lead AND the analog input pin on the other. then you just attach the 12v+ lead (brown) to 12v+, and the gnd lead (blue) to ground (preferably on the RC power, but the gnd on the DB 25 works too).
then when the sensor is off, (assuming you are connected the NO lead into the input pin) voltage flows from 5v+ through the 100K resistor and then because the switch is floating (or not connected to anything) into the analog input pin on the DB 25 connector. because the voltage goes into the pin, the RC reads 254, or 5v.
however when the sensor is on, voltage flows from the 5v+ thorough the 100k resistor and because the switch is closed to ground, the voltage goes into ground. the analog input pin reads 0, or 0v, because it is easer for the voltage to flow directly to ground then through the microprocessor's's A/D and then to ground.
the point of this whole explanation is to demonstrate that this is entirely possible, and even in some aspects simpler to implement in code then reading digital inputs. however, the same effect can be accomplished with out the added hardware by the following (theoretical for clarity) code:
DIGITAL_IN * 254 = DIGITAL_IN
this saves you $5, a trip to radio shack, and 4 minutes of soldering.
-Jacob
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