The Results of everyones help.

[John Fields]

On 17 Mar 2005 05:12:44 +0100, Roger Johansson <no-email@no.invalid>
wrote:

Roger Johansson <no-email@no.invalid> wrote:

"other person"
765,000

"original poster"
1,330,000

That's funny, a search on groups google seems to support your
interpretation stronger than mine.


Restricting the search to this newsgroup gives the numbers 48 and 50.
Still to your advantage but at least a lot closer to fifty/fifty.

---
If it were "Other Person" it would be too ambiguous to make any sense.
Which "Other Person" on the thread for instance? It could be anyone.

On the other hand, "Original Poster" is very specific and refers to
the person who started the thread, the original poster.

--
John Fields

 

[petrus bitbyter]

"Chris W" <1qazse4@cox.net> schreef in bericht
news:Y0xZd.17623$2s.9190@lakeread06...

Lord Garth wrote:

"Chris W" <1qazse4@cox.net> wrote in message
newsYtZd.17622$2s.3583@lakeread06...

I would like to thank everyone for all the help over the past little
while. I thought I would share the results of that help.

http://www.thewishzone.com/LightController/

I have put together my 256 light controller on prototype boards. Right
now it only controls 32 lights. It is expandable in 16 light
increments. It is made up of 3 basic parts. First there are up to 16
"Light boards", each will be stackable and control 16 lights. Then
there is the light board addresser. That will be on a PCB with the
micro controller and it will send a signal to each of the 16 light
boards. Finally the micro controller. I decided on the Rabbit
RCM3100. I know it is over kill, but I wanted to be able to program it
in C. Here are the details.

The "light boards" each have a 4 to 16 line decoder (CD74HCT4514) and 16
D type flip flops (SN74HCT74) wired up as toggle flip flops. All of
the, up to 16, light boards have the 4 LSB from an 8 bit output on the
RCM3100 hooked to the input of the 4 to 16 line decoder. The output of
the flip flops will go to either solid state relays or a transistors of
some kind to drive higher current loads.

The light board addresser has a slightly different 4 to 16 line decoder
(CD74HC154) the out puts of which go low instead of high. It gets it's
input from the 4 MSB of the 8bit output on the RCM3100. It's 16 outputs
each go to the enable input on the one of the CD74HCT4514s on the 16
light boards.

I can then program the RCM3100 to flash the lights in any pattern I can
dream up and I have dreamed up quite a few already. Of course I now
need to layout a PCB and have some made. First I need to design the
circuit that the RCM3100 will go in, with some kind of power supply
regulator and a few buttons to select different modes. The prototype
board is way too big for what I want to do with this other wise I could
just solder on a pin header and hook my boards to that.

The final result will be a remote control airplane that will be lit up
in manor that will put any Christmas tree to shame. I then plan to have
some fun flying it at night. The reason I want to have the lights flash
in all kinds of different patterns, is I intend on using the flashing
pattern as well as the LED colors to help keep track of the orientation
of the plane. Of course there is also the "cool factor"

--
Chris W


Chris, don't omit .1uF capacitors as near to the chip power pins as
possible.
The caps will help absorb power supply spikes that will screw the FF's up.

BTW, how big is this remote controlled plane? How many lights are to be
on
board the plane? An EPROM would be far simpler when used to store
patterns
directly.

It will probably have a wing span of around 6 feet, and be in the 7 lbs
range. It depends on the number of wing ribs(one set of LEDs between each
rib), but probably about 30 in each wing, maybe a few more down the length
of the fuselage. Then a few more in other various places like the wing
tip, vertical and horizontal stabilizer tips. For the wing, I will have
one or two in the leading edge and one or 2 behind the main spar with a
transparent film on the top and bottom of the back half of the wing,
between each rib. For the fuselage I will probably have one set down the
bottom and one down the length of each side. So probably some where near
100 total. Wow that is a lot


I'm having a hard time understanding how a simple eprom could do what I am
doing. So far I am up to about 240 lines of C code. I am a pretty good
programmer and I don't think I could cut down on that count by very much
and still do what I am doing. It is pretty hard to describe the patterns
I am trying to do, I could post the C code that will run from a command
prompt and display the wing light patterns with - and O for off and on.
Maybe you could look at that and tell me if I could use eproms.

--
Chris W

Gift Giving Made Easy
Get the gifts you want & give the gifts they want
http://thewishzone.com

Chris,

I may have missed a part of the discussion but looking at your hardware I
can't say but you're using a hell of a lot of electronics just to light some
LEDs. The classic way to light this amount of LEDs is by multiplexing. To
light 256 LEDs you need 32 output lines either directly from the
microcontroller or via registers like the HCT374. If you use four of the
latter you only need twelve output lines from the micro. The general idea is
to build a sixteen by sixteen matrix. So sixteen rows and sixteen columns.
On every point they cross you mount a LED that conducts from - let's say -
row to column. To switch the LEDs off, you keep the rows low and the columns
high, so all LEDs are blocked. Now to switch on some LEDS in a particular
column, you bring the corresponding rows high and then pull down the column.
You keep it that way for let's say 2ms then switch all off and select the
LEDs of the next column. On the electronic side of the project you need to
make the rows to be able to provide the current a LED needs along with a
current limiting resistor. The column driver need to be able to sink the
current for sixteen LEDs. Using discrete transistors is the easiest way. All
of the rest can be done in software, which seems to be your better skill.

petrus bitbyter

 

[Robert Monsen]

Chris W wrote:

John Fields wrote:

LEDs don't want voltage, they want a certain amount of current, and
when that much current is flowing through them the voltage across them
will be the specified Vf, or forward voltage.


I know that Vf is different for different LEDs, but doesn't E = I*R
apply to LED's.

R is simply the ratio of voltage to current. For a resistor, R is
designed to be nearly constant. However, this is not true for almost
anything else you can put current through.

The current of an LED is given by the Shockley diode equation:

I = Is * (exp(-Vf/(N*Vt)) - 1)

It's obvious from this that the voltage over current isn't anywhere near
constant for any LED. If the diode is conducting, and the voltage goes
up a tiny bit, the current will go up alot. Raising the voltage
something like 60mV will increase the current tenfold!

Thus, it's not practical to attach a diode to a voltage source without
some other way to limit the current which isn't so fussy about voltage
vs current. Usually, one uses a resistor in series with the diode.
However, there are other ways to go, like a constant current source.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Chris W]

Robert Monsen wrote:

Chris W wrote:

John Fields wrote:

LEDs don't want voltage, they want a certain amount of current, and
when that much current is flowing through them the voltage across them
will be the specified Vf, or forward voltage.



I know that Vf is different for different LEDs, but doesn't E = I*R
apply to LED's.


R is simply the ratio of voltage to current. For a resistor, R is
designed to be nearly constant. However, this is not true for almost
anything else you can put current through.

The current of an LED is given by the Shockley diode equation:

I = Is * (exp(-Vf/(N*Vt)) - 1)

Thanks, that makes it very clear. It's not that I can't supply the
correct voltage to get the correct current, just that the value is very
critical and probably varies from batch to batch, with temperature and
other factors beyond the control of my voltage supply. In this case I
am looking to get as much light out of the LED's as I can, but if I
weren't, couldn't I just supply a voltage that was enough lower than the
Vf to guarantee If was below 20ma and still get plenty of light for a
indicator or just testing on a prototype board? That way I wouldn't
have to have a resistor for every LED.

I'm glad I am getting this information before I get a regulator to
regulate the battery power going to my the LED's and circuit to control
the LED's in my RC plane.


--
Chris W

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
http://thewishzone.com

 

[Robert Monsen]

Chris W wrote:

Robert Monsen wrote:

Chris W wrote:

John Fields wrote:

LEDs don't want voltage, they want a certain amount of current, and
when that much current is flowing through them the voltage across them
will be the specified Vf, or forward voltage.




I know that Vf is different for different LEDs, but doesn't E = I*R
apply to LED's.



R is simply the ratio of voltage to current. For a resistor, R is
designed to be nearly constant. However, this is not true for almost
anything else you can put current through.

The current of an LED is given by the Shockley diode equation:

I = Is * (exp(-Vf/(N*Vt)) - 1)


Thanks, that makes it very clear.

You forgot the smiley...

It's not that I can't supply the
correct voltage to get the correct current, just that the value is very
critical and probably varies from batch to batch, with temperature and
other factors beyond the control of my voltage supply. In this case I
am looking to get as much light out of the LED's as I can, but if I
weren't, couldn't I just supply a voltage that was enough lower than the
Vf to guarantee If was below 20ma and still get plenty of light for a
indicator or just testing on a prototype board? That way I wouldn't
have to have a resistor for every LED.
I'm glad I am getting this information before I get a regulator to
regulate the battery power going to my the LED's and circuit to control
the LED's in my RC plane.

One problem with putting an LED on a voltage source is that the forward
voltage of the LED decreases as it heats up. Thus, if it starts to heat
up, it'll pass *more* current, causing it to heat up even more. This can
lead to failure.

Also, if you put a bunch of LEDs in parallel, one of them may pass
slightly more current, and will heat up, possibly leading to the runaway
scenario given above. Some will be dim. You just don't know. Also,
passing more current through an LED leads to premature dimming.

However, they are your LEDs. It may work if the voltage is adjusted just
right. I'll bet that the LEDs won't be consistently bright, but give it
a try, and let us know what happens.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Roger Johansson]

Chris W <1qazse4@cox.net> wrote:

Maybe this explanation is simple enough to understand for beginners:

A little condescending don't you think?

No. I don't have that kind of personality. I never feel offended by too
simple explanations. I like such explanations which let me work as
little as possible to understand something. And if I already understand
that issue I just jump to the next chapter.

If you are not a beginner, why do you read an article which starts with
the line above? And if you do, why complain when you find that it is
exactly that, an explanation for beginners?

Just because I don't have any
real education or experience in electronics, doesn't mean I'm an idiot.

I have no idea who you are or what education you have. I don't know if
you are the person who started this thread or somebody else. I reply to
questions in a newsgroup called sci.electronics.basics, intended for
beginners and hobbyists, and try to develop ways to explain things for
people with very little knowledge.

If you don't like explanations for beginners you can use a newsgroup
where you are expected to know the basics already, like
sci.electronics.design.

The most common question in sci.electronics.basics is "how do I use
an LED?" We see it seven times a week. So we try to find out how to reply
to that question in the most enlightening way possible, to people who
don't know anything about electronics, or about Google.

And especially to all the people with little knowledge who try to feed a
voltage instead of a current to a LED.

I don't talk to just one person when I write, there are other readers,
and people who search the usenet archives in the future, and I talk to
all of them. This is not email or a chatroom, it is usenet and I write
articles for all the readers, in the present and in the future.

I assume that other writers in the field of electronics read my
articles as well as I read their articles, and we learn new teacher
tricks and explanations from each other all the time. It is like an
experimental workshop in technical writing, and the person who started a
thread, usually referred to as "the other person" or the OP, because we
are too lazy to remember the names of all people who pass by, is maybe
less important than he thinks.


--
Roger J.