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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Tue, 29 May 2001 02:59:42 GMT
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Viewed:
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419 times
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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 simple software
solution is to time the transmissions. Continuous data bursts would be
acceptable, but should time out if they go on too long. Adding or
changing an internal resistor to limit the current through the IRLED
is a solution of course but it does so by dissipating some of the
energy through the resistor (in the form of heat) in order to
dissipate less through the LED. A better solution is to use one or two
extra LED's in series with the first. Each LED will provide about 1.2V
drop and will limit the current through both LED's, but will do so by
dissipating energy through the LED's as useful light, rather than as
wasted heat.
On another issue, I have both an RIS 1.5 and an RIS 1.0. Neither one
has an IR transmitter that accepts an external power supply. How did
you split off the power to both the RCX and the tower?
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.
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 haven't even connected the tower to anything yet, but it might be
just as marginal.
As an aside, I noticed that your signiture identifies you as a p.eng.
In what field? I gather (with all due respect) that it isn't
electronics?
Matthias Jetleb
VA3-MWJ
(who wanted to go into engineering (electronic communications) but
couldn't handle the calculus and settled for an electronic
communications technologist diploma - only to get a job in an
industrial controls company and now spend my time writing software -
go figure)
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Message has 2 Replies:
 | | RE: Custom Firmware, IR Problems, and Dead RCXs (long)
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| (...) The use of alternative firmware such as pbForth, legOS and leJOS usually requires frequent upload/download cycles, and may use long communications periods. (...) I agree on this point, but that will affect the low power range more as well. (...) (23 years ago, 29-May-01, to lugnet.robotics)
| | | Re: Custom Firmware, IR Problems, and Dead RCXs (long)
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| In lugnet.robotics, Matthias Jetleb writes: <snip...> (...) 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 (...) (23 years ago, 30-May-01, to lugnet.robotics)
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Message is in Reply To:
| | Custom Firmware, IR Problems, and Dead RCXs (long)
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| The following information is my own opinion and not endorsed or verified in any way by LEGO. That being said, I think that now is the time to relate some experiences I've had over the past couple of months with my RCX and IR tower - and it boils (...) (23 years ago, 27-May-01, to lugnet.robotics)
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