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 12:52:12 GMT
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Viewed:
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656 times
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Matthias wrote:
> 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.
The use of alternative firmware such as pbForth, legOS and leJOS
usually requires frequent upload/download cycles, and may use long
communications periods.
> 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.
I agree on this point, but that will affect the low power range more
as well. There would be extra light from the IREDs to compensate. The
RCX is pretty tight and I had some fiddling to do just to fit in the
resistor!
It is pretty easy to have a bug in your serial code that will cause the
IRED to be on for way longer than it should. I've had the RCX get warm
to the touch near the IRED (I'm guessing the drive transistor was
taking the brunt of the abuse)
> 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?
Using a Y cable and 9V battery clip and a sponge block to make it look
like a battery.
> 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.
Yes, this is a known issue. I've gone to using a regulator for the
supply from the wal-wart. Actually, I bough a regulated (5%) unit
from Digikey.
<snip>
> 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?
Ouch ... it's an Electrical Engineering degree from the University
of Waterloo - with a CS minor on top.
I'm aware of all the issues you bring up in this note, I just
summarized my points to open up the floor for discussion.
Obviously, if more folks like you can take the time to expand
on specific issues, it will help us all understand the problem
better.
Thanks for taking the time to read the original post and enter
a thought - provoking series of replies.
Regards, Ralph Hempel
--------------------------------------------------------------------
Check out pbFORTH for LEGO Mindstorms at:
<http://www.hempeldesigngroup.com/lego/pbForth>
Buy "Extreme Mindstorms: an Advanced Guide to Lego Mindstorms"
<http://www.amazon.com/exec/obidos/ASIN/1893115844/hempeldesigngrou>
--------------------------------------------------------------------
Reply to: rhempel at bmts dot com
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Message has 1 Reply:
 | | Re: Custom Firmware, IR Problems, and Dead RCXs (long)
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| (...) Oops. I just assumed that the RMS vs Peak value of an AC transformer and the subsequent consequences for the tower were so obvious that anyone with an electronics background would have pointed it out, and since you didn't, I figured you must (...) (23 years ago, 30-May-01, to lugnet.robotics)
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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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