Chip with simple program for Toy

"bgold12" <bgold12@gmail.com> wrote in message
news:16bcac37-c91c-4a5e-94e2-82fe21b9420b@m44g2000hsc.googlegroups.com...
Hey, I'm in 3rd year mechanical engineering and I still don't feel
like I have a strong understanding of what voltage is. Maybe someone
can help explain the concept.

I'm pretty sure I understand what charge is (it's just a fundamental
property of subatomic particles that affect the way they interact,
i.e. a charged particle induces a force on a surrounding charged
particle based on their charges (+e for a proton, -e for an electron,
and 0 for a neutron) and the distance and properties of the volume
between them), and I'm pretty sure I understand current, which is just
moving charges (I picture a bunch of electrons moving through a volume
between idle nuclei). But I don't get the concept of voltage. I know
it's produced from a separation of charges, and it is energy per
charge, or Joules/Coulomb, but where is the energy contained?
Click to expand...
Voltage is *potential* energy.
The most common analogy I've seen is with
that of water pressure. Think of voltage
as pressure, and current as flow. Resistance is
opposition to, or restriction of current (e.g. with
the water analogy, a smaller diameter pipe).
That's why the greater the amount of resistance,
the greater the voltage you'd measure across
the resistance.

-Mike
 
Michael Black <et472@ncf.ca> writes:

Commercially, the only really long standing use seems to be triggers
in oscilliscopes.
Click to expand...
I know one VARIAN Raman-Spektrometer with a TD in it's cicuit.
Probably in some sort of discriminator/trigger.

That's the only real use anyone has posted about
in these newsgroups in over a decade.
Click to expand...
That was about 1975...

Yours, Holger
 
"bgold12" <bgold12@gmail.com> wrote in message
news:16bcac37-c91c-4a5e-94e2-82fe21b9420b@m44g2000hsc.googlegroups.com...
Hey, I'm in 3rd year mechanical engineering and I still don't feel
like I have a strong understanding of what voltage is. Maybe someone
can help explain the concept.

I'm pretty sure I understand what charge is (it's just a fundamental
property of subatomic particles that affect the way they interact,
i.e. a charged particle induces a force on a surrounding charged
particle based on their charges (+e for a proton, -e for an electron,
and 0 for a neutron) and the distance and properties of the volume
between them), and I'm pretty sure I understand current, which is just
moving charges (I picture a bunch of electrons moving through a volume
between idle nuclei). But I don't get the concept of voltage. I know
it's produced from a separation of charges, and it is energy per
charge, or Joules/Coulomb, but where is the energy contained? How does
the coulomb of charged particles "have" this energy, and how is it
possible that there can be different amounts of energy associated with
a fixed amount of charged particles (i.e. you can have 10 joules/2
coulombs = 5 volts, but you can also have 20 joules/2 coulombs = 10
volts?)?

I hope that was clear, but it probably wasn't.

Thanks,

bgold12
Click to expand...

Have you looked at Wikipedia yet (http://en.wikipedia.org/wiki/Voltage)?
You might find that entry helpful.

The energy is contained in the electric field, more-or-less by definition:
the 'field' is a region in which forces act on charges. But if you seek a
physical explanation of why there should be forces at all then you may never
find a clear, simple explanation, as with gravitation.

Chris
 
"bgold12" <bgold12@gmail.com> wrote in message
news:16bcac37-c91c-4a5e-94e2-82fe21b9420b@m44g2000hsc.googlegroups.com...
Hey, I'm in 3rd year mechanical engineering and I still don't feel
like I have a strong understanding of what voltage is. Maybe someone
can help explain the concept.

I'm pretty sure I understand what charge is (it's just a fundamental
property of subatomic particles that affect the way they interact,
i.e. a charged particle induces a force on a surrounding charged
particle based on their charges (+e for a proton, -e for an electron,
and 0 for a neutron) and the distance and properties of the volume
between them), and I'm pretty sure I understand current, which is just
moving charges (I picture a bunch of electrons moving through a volume
between idle nuclei). But I don't get the concept of voltage. I know
it's produced from a separation of charges, and it is energy per
charge, or Joules/Coulomb, but where is the energy contained? How does
the coulomb of charged particles "have" this energy, and how is it
possible that there can be different amounts of energy associated with
a fixed amount of charged particles (i.e. you can have 10 joules/2
coulombs = 5 volts, but you can also have 20 joules/2 coulombs = 10
volts?)?

I hope that was clear, but it probably wasn't.

Thanks,

bgold12
Click to expand...
Note that everything you have learned about gravity can almost be directly
applied to electricity. In fact the governing equations of EM are almost
exactly the same as that of gravity if you could "remove" the polarity
aspect. (but the consequences can be dramatically different)

Electrons have attraction and repulsion while "matter" has only attraction.

What causet he attraction/repulsion? It is a force. Gravity on one hand and
the electrostatic force on the other.

What about potential energy? Same thing holds for charge. If you take two
charges and bring them close together they will have some sort of potential
energy... they will either attract or repell and that potential will be
converted into kinetic energy just as in mechanics.

Now voltage is a measure of that attraction.

How do you know something has potential energy? You have to let act out on
it. (there is no other way except through analysis but that came about from
observation.

Voltage, or the electric potential(vs the mechanical potential) is a really
a difference in potential energy.

So suppose we have +Q C at (-1, 0) and -Q C at (1, 0), they will attract
each other and have forces on them. this would be simiar case to M kg and M
kg but the magnitudes of hte forces would be different.

This attraction gives rise to a potential and the potential difference is
precisely the voltage. (in the right units for charge)

People tend to speak of voltage as if it were a force(such as electromotive
force which has the same units as voltage) but it is not a force just as
mechanical potential isn't a force... but it can be used to create a force.


You hopefully know that the gravitational force can have an associated
potential with it(the mechanical potential). The same is done with the
electric force. Since the forces are conservative we know by mathematics
that there is a scalar field who's gradient is the force. It's much easier
to work with a scalar field and it's called the potential.

In any case thats more theoretical.

What does it mean in practice?

If someone says that they have a capacitor with 10V "across" it what do they
mean? It means they can do some work... and if they were smart they could
compute just how much work. All you need ot know is that if there is a
potential difference between two points, any two points, and you stick a
wire at those two points(a conductor) then current will flow. If you have a
lightbulb or led in series with that wire then it might light up... or you
might be able to turn a wire.

The mere fact that there is a potential difference implies that you can do
work and vice versa. (they are identical concepts as force but viewed from a
different perspective)

It doesn't tell you have much work you can do and infact you might not be
able to do any depending on the circumstances... but at least in theory you
can do some work.

It also is related to current... because current flowing means there is a
potential difference. (but not vice versa)

Analogy: A book on a table. The table is a resistance to the book "flowing"
down to the ground. The book has potential due only to it's position w.r.t
to the earth. If you remove the table the book will convert the
potential(voltage) into kinetic energy(think of current) and when it hits
the ground or something inbetween it would apply a force that can continue
to do work on other things.

There is nothing special about voltage... it's just what we call the
potential for electricity. If you understand the gravitational potential
then you shouldn't have any problem if you just realize that the basic
quanitities one is dealing with are analogous. current = mass flow, voltage
= mechanical potential, force = force, electric field = gravitational field,
etc..

What's more important is that you have some concept of magnitude of
voltage... what is 10V? what is 1000V? Also helps to know something about
current and what is 1A vs 100A, etc...

By having that kinda knowledge you'll have a better working understanding.
It's similar to mass and energy. Everyone knows what 100lbs is about... or
maybe even 1000lbs but most people don't know much about energy. Most people
have a better concept of power than energy as they know their lightbulb is
using maybe 100W. They still don't really have any clue what it means but
they do know it is doing something(i.e. work).

And that's all this boils down too... voltage is a measure of work! Work is
what is important! mass is useless if it can't do any work! current is
useless if it can't do any work!! Current is a measure of charge in
motion... which is usefull to determine how much work it can do.

So ultimately in all the things we are trying to do is to simply things to
determine how much work something can do... by knowing that we know how much
less work we have to do. But of course we can't always measure work
directly... we don't have a special machine that we can ask how much work x
is doing and it tells us. We have to break the problem down and learn how to
measure it which involves measuring bits and pieces.


(I don't mean to sound dramatic about it but the fundamentals of physics is
concerned with it)
 
"Mike Wahler" <mkwahler@mkwahler.net> wrote in message
news:foedncQqwvRknXzVnZ2dnUVZ_qrinZ2d@earthlink.com...
"bgold12" <bgold12@gmail.com> wrote in message
news:16bcac37-c91c-4a5e-94e2-82fe21b9420b@m44g2000hsc.googlegroups.com...
Hey, I'm in 3rd year mechanical engineering and I still don't feel
like I have a strong understanding of what voltage is. Maybe someone
can help explain the concept.

I'm pretty sure I understand what charge is (it's just a fundamental
property of subatomic particles that affect the way they interact,
i.e. a charged particle induces a force on a surrounding charged
particle based on their charges (+e for a proton, -e for an electron,
and 0 for a neutron) and the distance and properties of the volume
between them), and I'm pretty sure I understand current, which is just
moving charges (I picture a bunch of electrons moving through a volume
between idle nuclei). But I don't get the concept of voltage. I know
it's produced from a separation of charges, and it is energy per
charge, or Joules/Coulomb, but where is the energy contained?

Voltage is *potential* energy.
The most common analogy I've seen is with
that of water pressure. Think of voltage
as pressure, and current as flow. Resistance is
opposition to, or restriction of current (e.g. with
the water analogy, a smaller diameter pipe).
That's why the greater the amount of resistance,
the greater the voltage you'd measure across
the resistance.

-Mike
Click to expand...
Not quite: Voltage is NOT potential energy nor is it kinetic or any other
kind of energy. Voltage is NOT energy.

Your pressure analogy is a good one however. Keep in mind that pressure is
not energy either.

Voltage in analogous to pressure or force sometimes called electro-motive
force, emf.

Current is analogous to flow rate.

Charge is amount or quantity of electricity.
 
<BretCahill@peoplepc.com> wrote in message
news:2fdb6bf1-ad64-40b8-852a-5f99c21304f7@w7g2000hsa.googlegroups.com...
The fuel tanks on commuter vehicles are over 4% of gross vehicle
weight. It's generally less than 0.5% on semi rigs. The semi can go
3 - 4 times further on a tank of fuel than the commuter. DOT regs
tend to reduce the distance even more.

We need to focus on a cheap battery even if it is inefficient.


Bret Cahill

Bret,
Click to expand...
Tell me about LiFePo batteries.
Mike
 
<jalbers@bsu.edu>

I can see how a capacitor would allow current to flow back and forth
in a circuit containing a capacitor connected in series with a
resistor. I know that current does not cross the dielectric. But
what if you throw a diode (transistor BE) in series with a resistor
and a capacitor. I don't see how this would allow current to flow
back and forth.
Click to expand...

** It won't, unless the diode is forward biased with DC current like it is
in your circuit - then a small AC current ( modulating the bias current
level ) can flow without causing the diode to stop conducting.

Another tip: think of a coupling cap as a battery with fixed DC voltage
that simply moves an AC voltages from one place to another where different
DC levels exist.



...... Phil
 
....
Nice job. Now he can go into fourth year.
No wonder our bridges are falling down.
Click to expand...
When did one have to understand electricity to understand how to build a
bridge?


I'd rather the guy know squat about electricity and be a great bridge
builder than build shitty ass bridges cause he spent to much time trying to
learn about electricity for some school requirements to "broaden his
horizons". He could have spent that time more wisely.
 
<porkysh1t@yahoo.co.uk> wrote in message
news:7beffb66-b11a-4602-a416-a44107a28d19@59g2000hsb.googlegroups.com...
right what i need is a diagram for the conditions i need... let me
explain

i need to press and release a NO switch and after certain time like
say 15 mins i need it to engage a relay for say 5 mins then disengage
the relay and wait for the push button again after.
**i could go as far as opto-isolation as it doesnt need much current
for switching but it does need seperation

many thanks
Ian

ps i seen many diagrams with this tan and other but there talking
beyond what need to know.. i got a strong guess i need 2x555 and
perhaps what they call a "flip flop" circuit unless anyone has a
better idea?
Click to expand...
A CMOS 556 would work, but since you don't need to know how it works, just
purchase a timer at the store.
Another idea is to scavenge a microwave oven control board, save the keypad.
I've done it and it will do what you want.
 
"Paul Hovnanian P.E." <paul@hovnanian.com> wrote in message
news:48E164E8.DE1CDFED@hovnanian.com...
If you tell me where the potential energy goes when I lift a weight up
in a gravitational field, I'll tell you where the energy goes when you
separate two charges.

It goes into the field! At least thats what field theorists say. They say
Click to expand...
the field is what has the energy... but of course they only say this because
the that is how they interpret the field equations ;/ (has to do with the
fact that potential energy depends only on the relative positions)

But to answer your question, when lift up a weight in a gravitational field
you are supplying work, i.e. energy, to the weight giving it potential
energy... you did that by first giving it kinetic energy to move it. So you
have actually increased it's potential energy... hence it's not "where did
the potential energy go" but "where did it come from" ;)
 
----------------------------
"bgold12" <bgold12@gmail.com> wrote in message
news:16bcac37-c91c-4a5e-94e2-82fe21b9420b@m44g2000hsc.googlegroups.com...
Hey, I'm in 3rd year mechanical engineering and I still don't feel
like I have a strong understanding of what voltage is. Maybe someone
can help explain the concept.

I'm pretty sure I understand what charge is (it's just a fundamental
property of subatomic particles that affect the way they interact,
i.e. a charged particle induces a force on a surrounding charged
particle based on their charges (+e for a proton, -e for an electron,
and 0 for a neutron) and the distance and properties of the volume
between them), and I'm pretty sure I understand current, which is just
moving charges (I picture a bunch of electrons moving through a volume
between idle nuclei). But I don't get the concept of voltage. I know
it's produced from a separation of charges, and it is energy per
charge, or Joules/Coulomb, but where is the energy contained? How does
the coulomb of charged particles "have" this energy, and how is it
possible that there can be different amounts of energy associated with
a fixed amount of charged particles (i.e. you can have 10 joules/2
coulombs = 5 volts, but you can also have 20 joules/2 coulombs = 10
volts?)?

I hope that was clear, but it probably wasn't.

Thanks,

bgold12
Click to expand...
Voltage is work (or energy) per unit charge required to move a unit charge
from a to b in an electrical field. An electrical field is produced by the
presence of other charges.
Think of mechanical potential energy per unit mass required to move a
unit mass from point a to b in a gravitational field. A gravitational field
is produced by other masses.

The two are analogous. In both cases it doesn't matter what path you take
from a to b.

--

Don Kelly dhky@shawcross.ca
remove the X to answer
 
According to the California Department of Consumer affairs, the initial
PE exam pass rate is lower for EE's than for any other branch of
engineering. Having found the exam relatively easy, I had a hard time
believing that. Nevertheless after seeing many of the posts on this
subject, I am no longer surprised.

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!
 
In article <gkhEk.2759$be.1230@nlpi061.nbdc.sbc.com>,
"Jon Slaughter" <Jon_Slaughter@Hotmail.com> wrote:

...
Nice job. Now he can go into fourth year.
No wonder our bridges are falling down.

When did one have to understand electricity to understand how to build a
bridge?


I'd rather the guy know squat about electricity and be a great bridge
builder than build shitty ass bridges cause he spent to much time trying to
learn about electricity for some school requirements to "broaden his
horizons". He could have spent that time more wisely.
Click to expand...
One reason to know something about electricity, that many EE's might not
know, is to understand corrosion and cathodic protection. A few years
ago, I saw a railroad bridge that was so rusted out that it would have
scared the hell out of me if I had to ride over it. Similar problems
exist in highway bridges. It really becomes scary when you think of what
improper protection of rebar could do.

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!
 
<jalbers@bsu.edu>
"Phil Allison" >
I can see how a capacitor would allow current to flow back and forth
in a circuit containing a capacitor connected in series with a
resistor. I know that current does not cross the dielectric. But
what if you throw a diode (transistor BE) in series with a resistor
and a capacitor. I don't see how this would allow current to flow
back and forth.

** It won't, unless the diode is forward biased with DC current like it is
in your circuit - then a small AC current ( modulating the bias current
level ) can flow without causing the diode to stop conducting.

Another tip: think of a coupling cap as a battery with fixed DC voltage
that simply moves an AC voltages from one place to another where different
DC levels exist.
Click to expand...
I never realized that a forward biased diode could pass current in
both directions.

** You still don't - cos it cannot.


I have always believed that current can flow in only one direction at
a time in a section of wire.

** Correct.


We can think of multiple currents
flowing down a section of wire in different directions like when
applying the superposition theorem but there is only "one" current
flowing in "one" direction which would be the algebraic sum of the
individual currents. Is this way of thinking correct?

** At any instant in time, the current flow has one value and one
direction.

If this is true, then how can current flow backwards through the
forward biased diode?


** You need to go look up the word " modulation" in a dictionary.

The current flowing in that base-emitter diode never changes direction -
it only changes amplitude.

There is an average DC value plus a smaller AC value superimposed -
MODULATING the DC value at any instant in time.

Think of a lake full of water - with waves on the surface.

It is THAT simple.



...... Phil
 
"Rose" <couple7802002@yahoo.com> wrote in message
news:8330c3a1-566d-457a-92b2-aa521f4455b1@l64g2000hse.googlegroups.com...
On Sep 29, 9:48 pm, "Jon Slaughter" <Jon_Slaugh...@Hotmail.com> wrote:
...

Nice job. Now he can go into fourth year.
No wonder our bridges are falling down.

When did one have to understand electricity to understand how to build a
bridge?

I'd rather the guy know squat about electricity and be a great bridge
builder than build shitty ass bridges cause he spent to much time trying
to
learn about electricity for some school requirements to "broaden his
horizons". He could have spent that time more wisely.
Click to expand...
So are you trying to say that learning about electricity
is not a wise use of time?

---

Of course not... But that you seem to imply that if he doesn't know
electricity that he can't build a good bridge which makes no sense.

But for practical reasons not everyone can learn everything or even one
person learn everything. Obviously knowing a bit about basic electronics
doesn't take much time though.

Bridge building requires absolutely no knowledge of electricity(theory wise)
and even if it did use a bit(say for lighting) it is not fundamental to
building bridges and others can handle that.
 
"Salmon Egg" <SalmonEgg@sbcglobal.net> wrote in message
news:SalmonEgg-074EF6.23091629092008@news.la.sbcglobal.net...
In article <gkhEk.2759$be.1230@nlpi061.nbdc.sbc.com>,
"Jon Slaughter" <Jon_Slaughter@Hotmail.com> wrote:

...
Nice job. Now he can go into fourth year.
No wonder our bridges are falling down.

When did one have to understand electricity to understand how to build a
bridge?


I'd rather the guy know squat about electricity and be a great bridge
builder than build shitty ass bridges cause he spent to much time trying
to
learn about electricity for some school requirements to "broaden his
horizons". He could have spent that time more wisely.

One reason to know something about electricity, that many EE's might not
know, is to understand corrosion and cathodic protection. A few years
ago, I saw a railroad bridge that was so rusted out that it would have
scared the hell out of me if I had to ride over it. Similar problems
exist in highway bridges. It really becomes scary when you think of what
improper protection of rebar could do.
Click to expand...
True... but that is not inherent to bridge building. Bridge building is
about choosing the right materials and dealing with the forces which has
nothing to do with electricity. Although your point shows that what I said
is not completely true.

I'm not saying electricity is useless and I'd rather everyone know much as
they can about everything... but if you gotta choose to split of your time
or not then it's usually best to not.

Although usually learning the basics doesn't take that long. My point wasn't
about learning electricity but about roses statement that implied the guy
couldn't build a good bridge if he didn't know about it... which is
ridiculous.
 
"krw" <krw@att.bizzzzzzzzzz> wrote in message
news:MPG.234b62ace17ca7e698a24b@news.individual.net...
In article <gkhEk.2759$be.1230@nlpi061.nbdc.sbc.com>,
Jon_Slaughter@Hotmail.com says...
...
Nice job. Now he can go into fourth year.
No wonder our bridges are falling down.

When did one have to understand electricity to understand how to build a
bridge?

Mechanical engineers don't build bridges either. They do build
automobiles and robots, though. Basic electricity would seem to be
a useful thing for MEs. Basic physics is rather useful, and
required, for EEs. MEs don't have to take the EM semester of
physics?
Click to expand...
Ok... yes, I know that. Alhtough the overlap is much greater. Learning about
your statics and dynamics is a major part of ME and CE'.

My response was specifically to the statement by Rose.

I'd rather the guy know squat about electricity and be a great bridge
builder than build shitty ass bridges cause he spent to much time trying
to
learn about electricity for some school requirements to "broaden his
horizons". He could have spent that time more wisely.

Try a civil engineer if you want a bridge built. I'd rather my
civil engineer had the full load of physics too. We *are* talking
about basic electricity here.
Keith
Click to expand...
True... but again, my statement was specifically about roses statement.

He/She is implying that if you don't know even the basics of electricity
then somehow you can't build a good bridge.

What I'm implying is that if the guy is an amazing bridge buildering(Ok, I
know he's ME but Rose is the one who brought up the bridge building) then
it's ok for him to suck as EE.

I'm sure Tesla sucked at ice hockey but I don't see anyone complaining that
he should have spent more time on it. (What does ice hockey have to do with
EE? Who knows but thats not the point)

Also we are getting off the point as if the guy is suppose to be the best.
There are many EE's that don't even have a good understanding of their own
craft so we should get onto those guys first.
 
jalbers@bsu.edu wrote in message ...
I am studying transistor amplifiers, specifically for the moment
Common Emitter with fixed resistor bias. For example Vcc = 15V, Rb =
200K, RC = 1K, Beta = 100 , capacitor coupled input connected to an AC
signal +/- 0.5V for example.

I think that I understand the load line characteristic curve stuff.
Ic will be centered at 7.15 ma and Vce will be centered around
7.85V . I believe that Vbe will fluctuate between .65V and .75V and
Ib will fluctuate above and below 71.5 uA by some value ?? . I guess
this could be determined by plotting a diode curve.

My problem is with the capacitive input coupling and the current flow
and how Vbe changes from .65V through .75V as the book seems to
indicate. Every book and source that I have kind of waves their hands
and says that the capacitor removes the DC bias and allows AC to
flow. The way that I think is to draw many pictures of the same
circuit and think of instances of time with concrete values for the
voltages, currents, direction of currents all over the circuit.

I can see how a capacitor would allow current to flow back and forth
in a circuit containing a capacitor connected in series with a
resistor. I know that current does not cross the dielectric. But
what if you throw a diode (transistor BE) in series with a resistor
and a capacitor. I don't see how this would allow current to flow
back and forth. I guess I need someone to break it way down so that I
can understand it.

Any help would be greatly appreciated. Thanks.

If you apply a 600 millivolt DC bias to the base emitter junction, and then
Click to expand...
add a 200 millivolt peak to peak AC input signal, the base emitter junction
sees a DC signal that varies from 500 millivolts to 700 millivolts. The
input signal does not reverse bias or reverse the polarity at the base
emitter at any time. It is common practise to call the varying part at the
base an AC signal or AC component even though it doesn't actually change
direction. Under these conditions, it would be possible for the entire input
signal to amplified and reproduced at the collector. This is called a Class
A amplifier.
There are amplifiers that do not reproduce the entire input signal at the
output. Sometimes an amplifier might only reproduce half of the sinewave or
just the tip of the sinewave at the output. These are called Class B and
Class C amplifiers. Under these conditions, the BE junction might actually
be reverse biased.
 
"Cardinal" <john.menken@ceridian.com> wrote in message
news:a9aad2df-b5ad-40a1-aa1a-069406f670d8@l62g2000hse.googlegroups.com...
I have a little 30rpm motor that I use to turn fishing rods when
applying epoxy to the guides. Unfortunately the 30rpm seems a bit too
fast. Ideally it would be slower like 10 or 12 rpm. Is there any way I
can slow it down? Someone told me a rheostat but when I went to price
one at the local flea market it was $13 and had a foot pedal and I'm
not at all sure that would work. Any advice would be most welcome.
Thank you very much.
Click to expand...
A proper rheostat would work but wastes power. All it does is end up
dropping the voltage across the motor or equivalently reducing current to
the motor... but will dissipate power in rheostat and it might be too much.

A simple fix: Try a lightbulb or two in series. This will reduce the
current and the bulbs usually dissipate the power easily and it can be
helpful to light up something too ;) (although it might be too much or too
little and it generates a lot of heat) (this is very similar to the rheostat
but you know it will be able to handle the voltage if it's 110V)

A better fix: Get a Variac. It lets you step up/down the voltage to whatever
you need... it's like the rheostat but doesn't dissipate nearly as much
heat... but can be expensive.

Best solution: Use a triac to lower reduce the average voltage. This
basically turns on and off the motor very quickly. By varying the
ratio(called the duty cycle) of the on to off you can vary the speed(in
proportion). It can be controlled by a simple potentiometer and usually
waste very little power.

I imagine you can find something that uses a triac at home depot or lowes.
They are used in dimming circuits for lights. They'll probably charge you an
arm and a leg so alternatively you could buy it online:

Info on operation:
http://www.ubasics.com/adam/electronics/doc/phasecon.shtml

http://www.epanorama.net/documents/lights/lightdimmer.html

(make sure the dimmer you get is solid state based else you get a
rheostatic)
 
"Cardinal" <john.menken@ceridian.com> wrote in message
news:a9aad2df-b5ad-40a1-aa1a-069406f670d8@l62g2000hse.googlegroups.com...
I have a little 30rpm motor that I use to turn fishing rods when
applying epoxy to the guides. Unfortunately the 30rpm seems a bit too
fast. Ideally it would be slower like 10 or 12 rpm. Is there any way I
can slow it down? Someone told me a rheostat but when I went to price
one at the local flea market it was $13 and had a foot pedal and I'm
not at all sure that would work. Any advice would be most welcome.
Thank you very much.
Click to expand...

If it's a 'split-phase' induction motor you might be able to take further
what Studer Revox did in the A77 (see
http://www.audioschematics.com/revox.html): put a bridge rectifier in series
with one of the windings and a transistor across the DC legs of the bridge,
biasing the transistor to get the desired (lower) speed. A Triac would
achieve the same effect, but in a time-discontinuous way. But if the load
is constant, surely any sort of effective series resistance will achieve
some reduction in the speed, albeit with potentially great inefficiency -
perhaps OK if the load consumes only a watt or so?

Chris
 
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