Wes Stewart wrote:

On 5 Jan 2005 17:07:51 -0800, "Cecil Moore" wrote:
|Slightly off topic - I've seen a couple of new automobiles with
|time-multiplexed LED taillights. What would be the advantage of such a
|design in an automobile?

What the hell is "time-multiplexed"?

In this case, on half the time and off half the time at about
a 100 Hz rate. Maybe square-wave power? Maybe pulse-width
modulation, different from night to day? I thought it was a
simple question to which someone had a simple answer.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
Wes Stewart wrote:

On 5 Jan 2005 17:07:51 -0800, "Cecil Moore" wrote:
|Slightly off topic - I've seen a couple of new automobiles with
|time-multiplexed LED taillights. What would be the advantage of such a
|design in an automobile?

What the hell is "time-multiplexed"?


In this case, on half the time and off half the time at about
a 100 Hz rate. Maybe square-wave power? Maybe pulse-width
modulation, different from night to day? I thought it was a
simple question to which someone had a simple answer.

"Time-multiplexed" means that they're turned on in sequence, without all
being on at once. That would be as opposed to simply pulse modulated all
at once.

My guess is that they're pulse modulated to provide easy and efficient
control of the brightness, and possibly compensation for voltage and/or
temperature. If they're time-multiplexed as well, that would even out
the total current drain rather than its being in the form of big current
pulses.

Are they really time-multiplexed, or are they all pulsed at once?

Roy Lewallen, W7EL

Roy Lewallen wrote:
"Time-multiplexed" means that they're turned on in sequence, without all
being on at once. That would be as opposed to simply pulse modulated all
at once.

The most trivial case of binary time multiplexing would be a
single LED being turned on for a logic 'one' and off for a logic
'zero'. That "binary time multiplexing" concept is a carry over
from 40 years as a digital engineer, 13 of them at Intel.

Are they really time-multiplexed, or are they all pulsed at once?

It appeared that they were all pulsed at once. Perhaps I should
have used the word "pulsed" to avoid confusion in the RF analog
(non-digital) world.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
Roy Lewallen wrote:

"Time-multiplexed" means that they're turned on in sequence, without
all being on at once. That would be as opposed to simply pulse
modulated all at once.


The most trivial case of binary time multiplexing would be a
single LED being turned on for a logic 'one' and off for a logic
'zero'. That "binary time multiplexing" concept is a carry over
from 40 years as a digital engineer, 13 of them at Intel.

Are they really time-multiplexed, or are they all pulsed at once?


It appeared that they were all pulsed at once. Perhaps I should
have used the word "pulsed" to avoid confusion in the RF analog
(non-digital) world.

Yeah, digicats have their own language. In analog parlance, multiplexing
basically means sharing. As in telephony, where you share one line among
many users by connecting each to the line for a short time in sequence
(time division multiplexing or TDMA - time division multiple access),
breaking the spectrum into pieces and giving each user his own channel
(frequency domain multiplexing), or more complex methods such as spread
spectrum code domain multiplexing, or CDMA (code division multiple
access). There's no sharing when there's only one user, channel, or LED
involved, so no multiplexing. Except, I guess, for digital types who can
share an LED between a 1 and a 0.

Just out of curiosity, what does your revered IEEE Dictionary have to
say about it?

Roy Lewallen, W7EL

Roy Lewallen wrote:
There's no sharing when there's only one user, channel, or LED
involved, so no multiplexing. Except, I guess, for digital types who can
share an LED between a 1 and a 0.

A two-wire serial ASCII RS232 line is time-multiplexed between
marks and spaces, i.e. you can't have a mark and a space occurring
at the same time. :-)

Just out of curiosity, what does your revered IEEE Dictionary have to
say about it?

I'm at the GED office presently. I'll check that when I get home.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
Roy Lewallen wrote:
Just out of curiosity, what does your revered IEEE Dictionary have to
say about it?

I'm at the GED office presently. I'll check that when I get home.

Well, looks like I win. The IEEE Dictionary agrees with you and you
have said in the past that the IEEE Dictionary is wrong. :-)
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:

Well, looks like I win. The IEEE Dictionary agrees with you and you
have said in the past that the IEEE Dictionary is wrong. :-)

Ah, binary again. I disagree with all entries or I disagree with none,
with no other possibilities. Spoken like a true digital engineer.

Indeed, I often disagree with that book, and don't feel that it does a
very good job of reflecting usage among working engineers. But
apparently on this issue I do agree with it -- a possibility only in my
analog world but seemingly not in your digital one.

Roy Lewallen, W7EL

On Fri, 07 Jan 2005 13:41:29 -0600, Cecil Moore
wrote:

|Roy Lewallen wrote:
| There's no sharing when there's only one user, channel, or LED
| involved, so no multiplexing. Except, I guess, for digital types who can
| share an LED between a 1 and a 0.
|
|A two-wire serial ASCII RS232 line is time-multiplexed between
|marks and spaces, i.e. you can't have a mark and a space occurring
|at the same time. :-)

Baloney. By this definition, OOK Morse is a "time-multiplexed"
system, eh?

Why not just Google this: define: multiplexing

Then try this: define: time multiplexed. And the answer is, "Huh?"

What you mean is that the LEDs are pulsed at some rate and/or duty
cycle. I wouldn't call this, "multiplexing."

|
| Just out of curiosity, what does your revered IEEE Dictionary have to
| say about it?

Took the words right out of my mouth, Roy. I almost asked that in the
previous post.

Wes Stewart wrote:
On Fri, 07 Jan 2005 13:41:29 -0600, Cecil Moore
wrote:

|Roy Lewallen wrote:
| There's no sharing when there's only one user, channel, or LED
| involved, so no multiplexing. Except, I guess, for digital types who can
| share an LED between a 1 and a 0.
|
|A two-wire serial ASCII RS232 line is time-multiplexed between
|marks and spaces, i.e. you can't have a mark and a space occurring
|at the same time. :-)

Baloney. By this definition, OOK Morse is a "time-multiplexed"
system, eh?

Why not just Google this: define: multiplexing

Then try this: define: time multiplexed. And the answer is, "Huh?"

What you mean is that the LEDs are pulsed at some rate and/or duty
cycle. I wouldn't call this, "multiplexing."

|
| Just out of curiosity, what does your revered IEEE Dictionary have to
| say about it?

Took the words right out of my mouth, Roy. I almost asked that in the
previous post.

Time Domain Multiplexing is where two or more signals share one data
pipe. Under TDM each signal is allocated one domain. Each domain is sent
in sequence. At the other end each domain is isolated and combined with
other domains elements from the same source. i.e. a, b, c fragmented and
sent as a1, b1 , c1, a2, b2, c2, a3, b3, c3 received and defragmented as
a, b, c. Commonly used to sent telephone conversations and internet
packets over copper wires and radio.

Dave WD9BDZ

Wes Stewart wrote:

Cecil Moore wrote:
|A two-wire serial ASCII RS232 line is time-multiplexed between
|marks and spaces, i.e. you can't have a mark and a space occurring
|at the same time. :-)

Baloney.

Didn't you ever use an 8 to 1 *MULTIPLEXER* chip to change
parallel BAUDOT to serial BAUDOT? The parallel BAUDOT bits
are time-multiplexed into a serial bit stream by the
three clock bits. The first parallel bit is hard-wired to
yield a start pulse and the last two parallel bits are hard-
wired to yield a stop pulse. The center five parallel BAUDOT
bits are time-multiplexed from parallel to serial by five
states of the clock.
--
73, Cecil http://www.qsl.net/w5dxp


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