April 2007:
If you are have a set of Cybermaster Touch Sensors hanging around, you can multiplex them for use on the NXT. For those that are unaware of these sensors, they are the
trans-green (clear) touch sensors that come with the Cybermaster kit and look similar to the standard MINDSTORMS RIS ones, but with one significant difference - each of them have an inline resistor so that
when the circut is closed, each passes through current with a different resistance.
Remember your electronics math? V = I x R? Well, when wired correctly (see below), you can have 3 of these sensors inline on one NXT sensor port. With a simple program using the
legacy temperature sensor, you can wire out the RAW data values use them to react according to which sensro was triggered. When no sensors are pressed, the reading will hover somewhere near
800. As you touch each sensor, the reading will change based on the resistance of that sensor. If you touch more than one sensor at the same time, the reading will adjust
based on the combined resistance of each sensor. Since each sensor has a different resistance, it is possible to have 8 combinations with various states. Now you can build
that multi-bumper rover and have 3 sensor ports free for other use!
The key to how to do this is how the electric cables are connected to each other. Use the below image for reference. If you only want to use 2 touch sensors, just take the
electric connector for the top sensor wire and connect it back to itself in the same direction (wire coming out of the right side).
The below image shows the output of the provided NXT-G RBT file (bottom).
Techno-Stuff has another version of a sensor multiplexer that works in a similar way. Have a look here for more information on this.
Of course to use this set-up, you will need the NXT <> RCX converter cable like the one below, or make your own.
Download Sample NXT-G Program
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