Subject:
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Re: RCX3 - Can extra hardware functionality be added?
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Thu, 27 Jan 2005 23:41:10 GMT
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Viewed:
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6034 times
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In lugnet.robotics.rcx, Paul Kleniewski wrote:
> hi
> so IMHO don't expect more outputs
> because of the power
> 3 motors + 3 sensors + mainboard have to be powered by bateries
I have a proposal that would theoretically allow an RCX to use 49 motors and 147
active sensors (or 588 switches!). This has the potential to control an entire
Ball Contraption or railway! The idea may be expandable to four times those
figures, depending how the signals are interpreted!
I'm thinking of multiplexing them via the speed setting from one or two motor
ports. This requires a clock to be generated that is eight times the PWM cycle
frequency but synchronised to the rising edge of the PWM. This is achievable,
subject to a few experiments. A counter would then count the number of periods
of the eight for which the output is high and convert it to a number for the
multiplexer. I decided to reserve the maximum speed setting of the control
ports for an emergency stop of all motors, driving the reset lines of the
counter latches.
If, as someone has commented, the motor ports' PWM outputs are not always
synchronised, I would put a clock generator on both control ports and
synchronise the latches that would hold the counter states for the decoders to
send to the multiplexer.
This expansion interface would require is own batteries, but with a power supply
it would be able to drive RC car motors or train motors, not just technic
gearmotors.
The 558 switches would be using my series resistor multiplexer, with values of
39k, 47k, 56k and 82k ohms, allowing any combination of the four switches to be
recognised with a reasonable margin to avoid errors.
The RCX program would set motor ports B and C to values corresponding to the
motor or sensors to be addressed, and would then set motor port A and read the 3
sensor ports. The speed settings of ports B and C would either use a cycle to
set and read all motors and sensors, or jump to values to address the ones
required. This is probably an application for alternative firmware, as
addressing 49 combinations and setting ports in a loop would be slow with an
interpreted language, as used by the original firmware.
If back-to-back opto-isolators were used on the motor ports, both directions
could be considered, giving each output 14 control states plus emergency stop,
allowing 196 motors, 588 active sensors or 2352 switches to be addressed!
> some time ago i proposed to make connectors smaller
> http://www.brickshelf.com/cgi-bin/gallery.cgi?i=631766
> first good think is the size of these connectors of course
> second is that they can be passed through the holes
>
> pixel
This is all very well, except that we've had 15 years of these connectors! I
don't expect them to change in the near future. Any connector design must be
large enough and robust enough for kids to handle repeatedly without failure,
and must comfortably handle the current required by an RC car motor (currently
their most powerful application).
I've made 9V to 12V conversion wires by putting 12V plugs onto cut 9V leads.
This way you can make your own leads with 12V plugs, putting the wires through
the holes before the plug goes on. It also means I can use my 12V wires on my
9V railway, reducing the amount of unused parts. Custom circuits can also be
plug and play with 12V plugs, and another advantage is that 1/0.6 bell wire can
be pushed into the ends between the 4 lobes for a temporary connection.
Mark
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