Subject:
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Re: Custom Firmware, IR Problems, and Dead RCXs (long)
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 30 May 2001 23:14:52 GMT
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Viewed:
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657 times
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In lugnet.robotics, Matthias Jetleb writes:
<snip...>
> Also, if you (or anyone else) are using an unregulated power supply,
> be forewarned: the rated voltage on most power supplies is the RMS
> value. That is to say a 12VAC transformer is supplying 12VAC RMS, not
> 12VAC Peak. That's 16.97V peak output voltage that the electronics
> within both the RCX and the IR transmitter has to be able to withstand
> - albeit momentarily. The RCX 1.0 is designed with this in mind (a
> bridge rectifier, good filtering and an 5V internal regulator that can
> has a guaranteed stable output with a 54V (that's fifty-four) input.
> What I can't say for sure is if they LED's within the RCX are
> connected to the output of the regulator (in which case they see no
> more than 5V) or to the input of the regulator (which could be almost
> 17V). I tend to think they may be connected to the input of the
> regulator because, while the regulator can withstand an input voltage
> of 54V, it can only supply a maximum of something like 50mA.
>
> Don't be too quick to quote me on this since I've got the specs
> written down somewhere, but I can't find them. I did post them to
> lugnet a while ago (either lugnet.robotics, lugnet.robotics.rcx or
> lugnet.robotics.rtltoronto). If you can't find it, I'll look around my
> desk for it.
>
> If you (or anyone) are using an AC adapter on the IR tower, be aware
> that the filter capacitor in the tower is only rated at 10V and is
> only intended to smooth out the ripples that will result from sending
> IR tranmissions. These will be much smaller than the 100% ripple from
> an AC adapter. More filtering will be needed. Also, a 12VAC adapter
> has an output that ranges from +17V to -17V. A bridge rectifier would
> have to be installed to make it +17V only. A simple diode, or 5V
> regulator will cause the power supply to the tower to be 0V for about
> 51% of the time.
>
> The tower uses two 74LS132's (IIRC) which will require a regulated 5V
> supply, so there must be a 5V regulator on the board (even if only a
> zener diode), but I haven't seen it yet so I don't know the ratings.
>
> Also, if the IRLED's on the tower are connected directly to the power
> supply, and not through a regulator (which I suspect is the case) then
> an AC supply will introduce a massive 60Hz ripple to the IR
> tranmission. I can see where this would cause some serious problems.
One important point that I haven't seen mentioned here is that the RCX AC
adaptor input is labelled "9-12V~", which is AC, not DC. I have used the
transformer that comes with the 9V train sets, which claims to output 12 VAC
at 7 VA. I know that the supply voltage will be rectified to DC for the
RCX, but if you're calculating power, remember that "the area under the
curve" for a flat-line DC signal will be a bit greater than the same area
for a sine wave.
> Finally, for what it's worth, my son was playing with my brand new
> RIS1.5 a couple of weeks ago. He's only 18 months old, so playing is
> limited to pushing the 'on' button and listening to the beeps. After a
> while he stopped playing an put it down. I though it was because he
> had become bored. It turns out it had stopped working altogether. No
> loads or sensor were ever connected to it. It just died after being
> turned on about 40 times. Apparently they'll just do that. I have to
> assume it's a common problem given that Lego is replacing it without
> any argument.
I read your account of this in a previous message. It sounds like you did,
but did you try taking out the batteries for awhile to kill the "firmware"?
I've seen cases where buggy (or perhaps corrupted) firmware causes the RCX
to hang so badly that it doesn't even recognize its own power switch. In
those cases, removing the batteries for a few minutes (or even removing just
one of the batteries for several seconds) will reset the RCX to its factory
condition, effectively erasing the corrupted memory image.
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Message is in Reply To:
 | | Re: Custom Firmware, IR Problems, and Dead RCXs (long)
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| I'm hard pressed to understand why one would need to continually transmit from either the RCX or the tower? Data logging comes to mind, but there aren't many cases where there is a need for this. Listening can, of course, be done continously. The (...) (23 years ago, 29-May-01, to lugnet.robotics)
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