The RCX Expander project page !

Note : this one will be completed within a year or so :-) because I don't have time enough to complete it... Contact me if you're interested.

The most common problem when developping RCX applications is the lack of inputs. This page is intented to add more inputs ( 7 analogic, and 3 for switch) by multiplexing two inputs from the RCX. This idea came from Sven Horstmann and Michael Gaperi. I'm only responsible for the practical approach, and eventually the PCB design and the "how-to-build" guide (not made yet...).

1. Goal of this project

2. How to ?

1. The goals :

To design a board which add more sensor inputs to the lego mindstorm RCX.
To create some NQC code to control the board.
To be simple enough to be constructed by any elecronics hobyist.
To be cheap.
To be available to anybody

More technically :
To use one or two RCX inputs and to multiplex them
To allow both passive and active sensors to be connected
To be small and smart enough to be placed in some kind of lego-partially-made box

...

FIGURE 1 : The basic idea. Note that at the moment, no solution has been found to give power for active sensors connected to the seven analog gates. The 3 touch sensors being passive, we don't have any problem here. I think it could be possible to use power from the input port B, and use it for port A, but we only have 30 mA, which isn't enough. Maybe with external power ? (A simple 9V battery could do the job)

2. How to :

Use two inputs : one (1) which is switched between passive/active sensor mode to control a counter (4017), this counter controling analogic gates (2 X 4066), and another one (2) in active (light sensor) mode (to provide power for active sensors connected on the first one?) The second inputs should be multiplexed for use with 3 touch sensors and 3 resistors.

3. The NQC software :

Basically, a task which can be added to any program, that fills 10 vars with :

Note that the first gate allways gives a value of 100 which is used to detect the start of the sensor reading loop.

4. Where to fit ?

To keep lego feeling, this add-on could be placed in a standard 9V lego battery box. The pcb will be designed to fit in. The connectors could be build using screws that fit in a standard lego pin. But it could be placed in a lot smaller box build with large lego parts glued together...

Note that any other lego box should (and will eventually) be used.