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'[EE] Will the questions never end?! ;) (small'
2002\07\11@152221 by Brendan Moran

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Yes.  It would be 10V  That's what parrallel ccts are all about.

- --Brendan


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2002\07\11@152827 by Kieren Johnstone

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Yay! ^_^  You must excuse me, I think I'm on a sugar high.
Okies, just thought of another question (after the natural "what's a cct")..
If I wanted to use a 5V PIC that uses < 0.6mA typically to switch on/off a
6V, 30mA laser module (I like lasers they're pretty), well.. how would I do
it? :)  Obivously I'd need a 6V (or more) source, no?  Would I then use a
voltage divider on one end to drive the PIC.. the laser would run off the
other parallel-ly connected circuit, but how would an outpin pin from the
PIC switch it?  I'm thinking "relay" but also "maybe that's a bit bulky".  A
transistor?  How would I connect it? :)

-Kieren


{Original Message removed}

2002\07\11@154956 by Kenneth Lumia

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Kieren,

Yes, 10V from the battery is always 10V, regardless of how many
parallel loads are attached (assuming the battery can supply the
current required).

Note that in your example, you are splitting the
10V by using a resistor divider.  The 4 and 6V are the drops ACROSS
the respective resistors, this is not the same as a 4V and a 6V supply.  In
particular, the 6Volts accross the left resistor is not referenced to the
batteries 0V or ground, and is instead actually  4Volts and 10V
above the 0V reference depending on which side you want to measure.

> If this is true, am I to assume that in general, people use 2 small,
> different value resistors in series, and run a load in parallel with one
of
> them to lower voltages? :D

No, absolutely not.  If you were to run a load in parallel with one
of the series resistors, it would change the effective resistance of that
portion of the circuit, and hence the voltage at the node. Have a look at
a basic circuits book, look around the sections dealing with
thevenin, norton theorems and node voltages.

Ken

{Original Message removed}

2002\07\11@160333 by Kieren Johnstone

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Huh, that changes things a bit.
How would I then obtain a lower voltage relative to ground?  Also, my book
doesn't cover thevin, nortons theorems or node voltages!  Just basic
components, resisitors in parallel/series, capacitors...  Could you suggest
a book?
My second post regarding operating higher-voltage loads is still begging for
an answer too ;)

Thanks

{Original Message removed}

2002\07\11@163717 by Kenneth Lumia

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> Huh, that changes things a bit.
> How would I then obtain a lower voltage relative to ground?

Use a linear voltage regulator; 10V in, 5 Volts out, the rest is
dissipated as heat.

>Also, my book
> doesn't cover thevin, nortons theorems or node voltages!  Just basic
> components, resisitors in parallel/series, capacitors...  Could you
suggest
> a book?

Well, its been almost 20 years since I took the classes, but any
college level circuit analysis book should do it.  You may want to
look at the following Schaums Outline book:

books.mcgraw-hill.com/cgi-bin/pbg/flypageSCH.html?mv_arg=0070478244&s
ectioncode=SCH

From what I recall, these books are typically formatted as a couple of
pages of theory and then 2 or 3 pages of worked problems,
great for a beginner.  Its not as inclusive as a typical text book,
but Schaums usually very well explains what is covered .
Note, I don't have this version of the book, the above is a
generalization from the distant past.

Ken

{Original Message removed}

2002\07\11@164257 by Harold M Hallikainen

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       One thing with voltage dividers... You have to consider loading. You
might have a look at some of the articles at
http://www.hallikainen.org/rw/theory/ . See especially the one on
Thevenin Equivalents.

Harold


FCC Rules Online at http://hallikainen.com/FccRules
Lighting control for theatre and television at http://www.dovesystems.com

Reach broadcasters, engineers, manufacturers, compliance labs, and
attorneys.
Advertise at http://www.hallikainen.com/FccRules/ .


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2002\07\11@165525 by Eoin Ross

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I don't want to be a stick in the mud ... but it sounds like you would be well served taking night classes at a local community college in basic electronics (or even try buying one of the secondhand textbooks for the courses)

A textbook I have that covers those theories and AC is called
"Electric Circuits" Author is "Bogart" Published by "Glencoe Publishing Co"
Not too cheap but you might score a used one. http://tartanstore.sinclair.edu has it for $85 used

>>> spam_OUTmisterfugitTakeThisOuTspamHOTMAIL.COM 07/11/02 04:00PM >>>
Huh, that changes things a bit.
How would I then obtain a lower voltage relative to ground?  Also, my book
doesn't cover thevin, nortons theorems or node voltages!  Just basic
components, resisitors in parallel/series, capacitors...  Could you suggest
a book?
My second post regarding operating higher-voltage loads is still begging for
an answer too ;)

Thanks

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2002\07\11@170402 by Kieren Johnstone

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Actually I start a course in September, but I had a "taster" session, got
really interested, and am trying to get a head start ;)
Books seem to be the answer for most problems, eh? :D

{Original Message removed}

2002\07\11@170410 by Lawrence Lile

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In all of my designs I have a higher voltage power source (9-24 volts) a 5V
regulator (78L05 or a zener, typically) and the PIC drives 24 volta loads
through a small open collector transistor (sized appropriately for the load)

--Larence


> My second post regarding operating higher-voltage loads is still begging
for
> an answer too ;)
>
> Thanks

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2002\07\11@172923 by Eoin Ross

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Do you have a list of the textbooks for that course ?
Books are OK ... but the tinkering with real devices applying what you just read
is the real ticket to understanding

PS - one thing to add to your list ... eye protection ; ) Some things do go bang hehe
And always use a wallwart/small batteries (A car battery has the capacity to "vaporise" a 10" crescent)

We want you to be around in one piece for a while

>>> .....misterfugitKILLspamspam@spam@HOTMAIL.COM 07/11/02 05:02PM >>>
Actually I start a course in September, but I had a "taster" session, got
really interested, and am trying to get a head start ;)
Books seem to be the answer for most problems, eh? :D

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2002\07\11@181125 by Francisco Ares

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"ccts" is a short form for "circuits".

I use to recomend for begginers to imagine a sort of association between
electrical and hydraulical systems:

- tension could be the height of a water container to the "ground", or
relative pressure (relative to ground, also, if you like);
- current could be the water flow rate in time;
- resistance coud be some kind of restriction in a pipe (and the pipe is
a wire);

So, in the first circuit one could say that you picked up a pipe out of
the "10V" tank to the first restriction, anoter pipe to the second and
then left open to the ground, so there is a water flow depending on
those restrictions; the lower those restrictions, the higher the flow
rate. You will also get pressure losses after restrictions and also
along pipes, because pipes are restrictions themselves, so do wires in
electricity, because there is no material (in normal conditions) that
has no resistance at all.

If you want to drive a load that has a different power supply than the
PIC or may drain more current than a PIC pin may deliver, you have to
build an interface that can be as simple as a transistor: the PIC pin
should be connected to the base terminal of a transistor through a
resistor (for current limiting), the emiter to the ground and the
colector to the negative pin of the load (your laser) and its positive
to the power supply. Let me try to draw it:

  +6V
  ---         DIODE
   |          |\ |
   |----------| >|-------------
   |          |/ |             |
   | +                         |
 LASER                         |
   | -                         |
   |                           |
 C  \ |                   -----------
     \|  B               |    VCC    |
      |----- R (10k) ----| PIC       |
     /|                  |           |
 E  / |                  |           |
   |                      -----------
   |
 -----
  ---
   -

As there is just a little difference in the supply voltages for the
laser and for the PIC (just 1V) you may use a diode as shown (I think)
above: the voltage drop in a normal diode is something like 0.6 to 0.7V,
and the PIC will work with something between 4.5 to 5.5V (if you want,
you may add another diode in series, just to be safe). The transistor
may be any general use NPN, or, if you like, a 2N2222 or a BC337.

You will have to look for the specs of the laser to make sure about the
voltage levels in which it works fine.

Hope this helps
Francisco


Kieren Johnstone wrote:

{Quote hidden}

>{Original Message removed}

2002\07\11@182941 by Brendan Moran

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> I don't want to be a stick in the mud ... but it sounds like you
> would be well  served taking night classes at a local community
> college in basic electronics  (or even try buying one of the
> secondhand textbooks for the courses)

I found when I was starting out in EE (it was the summer between
grade 10 and 11) that the green radioshack (*shudder*) book, though I
think they've changed the color now, was an excellent starting point.
If you want to go that route, Try to find the book that is pinted on
lined paper, with little drawings here and there.

The drawings are a bit childish, but the text is good, and it covers
important concepts.

They have several other texts as well, but I don't like them as much.
They are done in a more professional style, but aren't as good if
you ask me.

> A textbook I have that covers those theories and AC is called
> "Electric Circuits" Author is "Bogart" Published by "Glencoe
> Publishing Co" Not too cheap but you might score a used one.
> http://tartanstore.sinclair.edu has it for $85 used

If you do go with my Radio Shack suggestion, I recommend getting a
real textbook later as well, but I thought that that book would
likely be close to the kind of start you want.  It's gentle and fun,
it's not designed to pack your brain with as much information as fast
as possible like most texts are.

Good luck and good hunting!

- --Brendan

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2002\07\11@183332 by Bob Ammerman

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> Huh, that changes things a bit.
> How would I then obtain a lower voltage relative to ground?

A voltage regulator (see 7805, 78L05 for some oldies but goodies). There are
a gillion choices for these.

> Also, my book
> doesn't cover thevin, nortons theorems or node voltages!  Just basic
> components, resisitors in parallel/series, capacitors...  Could you
suggest
> a book?

Not off the top of my head.

> My second post regarding operating higher-voltage loads is still begging
for
> an answer too ;)

The simplest solution for this is probably a transistor. For your laser
diode case:

Use an NPN transistor (2N2222 or any other 'jelly-bean' type will be fine).

Connect emitter to ground (negative side of battery supply).
Connect base via a resistor (1K ohm should be Ok) to PIC pin.
Connect collector via a resistor(*) to the cathode of the laser diode.
Connect the anode of the laser diode to the positive side of battery supply.

* the value of this resistor is chosen to determine the current thru the
laser diode as per ohms law, as per the following formula:

Led current = (BatteryVoltage - LedForwardVoltage) / ResistorValue

LedForwardVoltage is a characteristic all LEDs (in fact all diodes) have. It
is the voltage that will be "dropped" by the LED when a current is flowing
thru it.

Now when the PIC pin is hi (5V) it will push current into the base of the
transistor. The transistor will then turn on like a switch effectively
connecting the collector and emitter together (a simplified explanation).

Bob Ammerman
RAm Systems

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