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In lugnet.robotics.cybermaster, Sandy Johnson wrote:
> In lugnet.robotics.cybermaster, Danny Staple wrote:
> > > Is it possible to interface a cybermaster and an RCX without the use of a
> > > PC, also without using up all sensor and motor ports?
> > >
> > > Sincerely,
> > > Morten H Pedersen
> >
> >
> > It might be theoretically possible to use one RCX sensor port for control
> > of the cybermaster - and using the one motor and one sensor port on the
> > cybermaster.
> >
> > Danny
>
> This might be old news, but I just tried it anyway...
>
> You can connect an RCX motor port to a CyberMaster sensor port and vice versa
> and get tri-state info. You can distinguish between the motor floating, off,
> and one of forward or reverse (seems to depend on the which way round things are
> connected). I haven't written any code for this, but I got reliable results
> from Brixcc's watch and command interfaces.
>
> The downside is that it takes one motor/sensor pair in each direction, which
> isn't great. I also have no idea if it's a safe thing to do or whether you
> eventually burn something out.
>
> The other downside is that with only 395 bytes of code in the CyberMaster, you'd
> want your messages to be very simple to keep the decoding code to a minimum.
>
> In my current project I have but 1 byte free in my CyberMaster... :-)
I think it's theoretically possible to communicate an 8 state signal from the
RCX to the Cybermaster's passive sensor port.
The passive sensor port measures resistance as well as using a switch - the 3
switches in the cybermaster set have resistors that enable it to tell which
implement is connected to the tracked robot.
Therefore if you output motor power 0-7 on RCX motor port B and smooth the
signal over the RCX PWM cycle time (1/166Hz = 6.024ms) using a filter, the
voltage will be in 8 levels from 0 to 9V. Use a transistor to turn that into a
resistance, with suitable biasing components to get the correct range (1kohm for
minimum, 100kohm maximum to get fairly linear range), and you'll get 8
resistance values on the cybermaster port, which will become 8 raw values when
the port is read.
The only problem then is decoding it in 395 bytes :-)
I'd like to use the cybermaster as a communications interface, so that I can get
a live link from the PC to the RCX even if it is in another room, without having
IR Tx/Rx equipment in every room. I would probably use this port to port
arrangement, smooth the PWM over its cycle time and convert it to a resistance
to get up to 8 messages to transmit to the PC, assuming it was compatible with
the software (I use visual basic with Spirit1.ocx at the moment).
The cybermaster is great for having more sensors with the shaft encoders, and a
radio interface, but is less versatile with having the motors fixed and only one
other output port and no active sensor capability.
I'd like a cross between a cybermaster and RCX, with lots of input and output
ports and a radio interface, and lots of RAM for programs! So far I've made a
4-way switch multiplexer that can distinguish any combination of 4 switches on 1
RCX port, but I'd like not to have to multiplex in order to get enough sensor
ports. How about 8 passive + 4 active ports in the next RCX, for 8 bumpers + 2
rotation and 2 light sensors on a robot?
At the moment an RCX circuit has separate chips on the board, but more
functionality could be put in the RCX if the whole circuit were put into a
hybrid package. Just the die from the chips would need to go in, saving space
and allowing more RAM chips and H-bridge motor drive circuits to be added.
I'd also like to see more power capability. The RCX will only just drive a
light train with all 3 motor ports connected in parallel. And of course, the
restoration of the AC input socket is a must. Having said that, perhaps more
power from the size is impossible, so a slave motor drive unit should be
developed, that would take power from a transformer and signal from the RCX and
beef up the power. Then driving trains with an RCX is a real possibility.
Mark
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