Chip with simple program for Toy

[Don Bruder]

In article <6rqrt01u7b9qmhv1827op05n1s9i00bnb2@4ax.com>,
AcCeSsDeNiEd <dillon@SpamMinuSaccessdenied.darktech.org> wrote:

Hi guys. I have a LCD monitor. I lost the power adaptor for it.
I bought a replacement.

My LCD monitor power requirements are: 24V DC, 2.4A

My power adaptor is: 24V DC, 5A Max.

Question is, if the adaptor is 5A max, will it blow my LCD monitor?

Not likely. Amp requirement is a minimum, not a maximum. A
bigger-than-required amp capacity will simply go unused, doing no harm.
A lower-than-required capacity may very well cook the supply, but
*USUALLY* won't do any harm to the device. Note the stress on
"usually"...

--
Don Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004.
Short form: I'm trashing EVERY E-mail that doesn't contain a password in the
subject unless it comes from a "whitelisted" (pre-approved by me) address.
See <http://www.sonic.net/~dakidd/main/contact.html> for full details.

 

[John Popelish]

Ricky Romaya wrote:

I want to design and build a very simple audio amplifier to drive my
8ohms speakers from (onboard) pc soundcard. I figure I'm using op-amps.
I'm a newbie and all I know about op-amps are basic, mostly from text
book.

Basically, I'm a little confused. Usually I see that the type of
amplifiers to drive speakers are called 'power amplifiers'. From the
basic building blocks of op-amps, I could only find circuits for voltage
and/or current amplifiers. Do those 'power amps' are really 'voltage
amps', cos I figure the main drive factor for speakers are voltage
variations (voltage are converted into air preassure by the speakers, and
hence creating audible sound)?

Yes, speakers are usually designed to be driven by voltage sources. A
voltage source is one that regulates the voltage applied to a load
(the speaker, in this case) while supplying whatever current is
required to apply that voltage across the load. If the speaker was a
resistive 8 ohms, that would mean that for every 8 volts the amplifier
applied across the load, it would have to deliver 1 ampere through
it. So just because it is a voltage source, does not mean that you
can neglect the current side of the equation, it just means that
voltage is what the amplifier regulates most precisely.

One of the big differences between a typical opamp and a power amp is
that the opamp has a maximum current capability somewhere between 10
and 30 milliamps while a power amplifier that operates from the same
supply voltage may have large enough output transistors to pass more
than an ampere.

Further more, I figure that the input stage of the amps I want to build
will simulate that of LINE-IN/AUX/CD-IN lines found on commercial sound
systems. Anybody knows whether there are standards to the input voltage
and input impendance of those lines (LINE-IN/AUX/CD-IN), and if there
are, what are the values? And how about output impendance standards for
driving 8ohms speakers?

Also, anybody knows how the input parameters (voltage, current, power) to
the speaker relate to the SPL (Sound Preassure Level) generated by it?
This indirectly means I'm asking the relationship of the amplifier gain
to the loudness of the sound generated by the speaker.

Last, but not least, what are the recommended op-amp series for audio
processing (I only know the multi-purpose u741 series)?

Well, that's a long list of questions, and there are more. Any help is
appreciated.

There are integrated power amplifiers (essentially high output current
capability opamps with some internal bias and gain setting resistors)
that are available for very little cash. I think you might start with
one of these for your experiments. The data sheets show the typical
speaker amplifier circuit diagram and additional parts needed.

Some examples:
http://www.national.com/ds/LM/LM380.pdf (one of the most common)
http://www.national.com/ds/LM/LM386.pdf (low voltage version of the
LM380)
http://rocky.digikey.com/WebLib/ST%20Micro/Web%20Data/TDA1905.pdf
http://rocky.digikey.com/WebLib/Panasonic/Web%20data/AN7513.pdf
http://rocky.digikey.com/WebLib/Panasonic/Web%20data/AN7511.pdf



--
John Popelish

 

[John Popelish]

Danny T wrote:

John Popelish wrote:

5. You should also have a capacitor between each motor driver fet
source and the positive end of its motor, to act as a small local
supply, so those high frequency on-off edges don't get back to the
battery and then into the PIC.
A .1 uf film or ceramic in parallel with a few hundred microfarad
electrolytic might be enough. A 1 uf film or ceramic in parallel with
a 1000 uf electrolytic would be better.

Which leg of the MOSFET should it connect to? Not sure I understand its
purpose :-\

The source lead. The caps connect between the positive and negative
supply points for the motor and its driver transistor (as close as
possible to those points, too). When the drive transistor turns off
or on, suddenly, a wave of current would otherwise travel all the way
back to the battery, bouncing every circuit connected to it.

Imagine sitting on a large trampoline, trying to read a book of fine
print, while a fat kid jumps on it a few feet away, to visualize the
effect the motor load will have on the PIC.

--
John Popelish

 

[Miles Harris]

On Sun, 02 Jan 2005 17:48:42 +0000, Danny T <danny@nospam.oops> wrote:

http://www.kpsec.freeuk.com/components/diode.htm

says

"There is a small voltage across a conducting diode, it is called the
forward voltage drop and is about 0.7V for all normal diodes which are
made from silicon. The forward voltage drop of a diode is almost
constant whatever the current passing through the diode so they have a
very steep characteristic (current-voltage graph)."

The forward voltage drop is entirely dependent on temperature (the
junction temp. of the p/n junction; which is in turn dependent upon
the current passed.) Higher currents equals higher temp. equals lower
voltage drop. It's a well known effect which can eventually destroy
the diode altogether. The physics of diodes is actually more complex
than a lot of texts would have you believe.

 

[Dominic-Luc Webb]

On Tue, 4 Jan 2005, Danny T wrote:

Andrew Holme wrote:

Well, I've answered your specific questions. I could go on, but this is a
MASSIVE subject. I recommend the book "The Art of Electronics" by Horowitz
and Hill if you fancy some good arm chair / bed time reading on the subject.
It's informal, readable and not at all stuffy or dry.

At Ł50, I think I'll see if the Library have it first ;-)

Ta!

Danny,

I just bought this book at Ebay for 27 brittish pounds with shipping
within USA... There were a number of copies of this book being sold
there. Be cautioned there is another, related book, maybe a lab manual,
etc, that sells for about half the price. If you go the auction route,
pay close attention to what people are wanting for shipping and handling,
and stick with people with a good record from previous deals.

Here is the one I got: Ebay #4515997432

There is another auction right now, even lower price. Just type in
the name of the book and you should find several examples, such
as: Item 4516689114

Dominic

 

[Sylvan Butler]

On Fri, 31 Dec 2004 06:00:23 GMT, W. Watson <wolf_tracks@invalid.inv> wrote:

I decided to buy a 60 minute timer at the local h/w store and a two outlet socket. I

That's what I did.

figured I could put this in an electrical connection square metal box with a 3-prong

The metal box should work fine. (Don't forget to ground it.) Only
caveat, is that normally the devices mount to the cover instead of the
box, or else to a secondary ring (box, ring+devices, cover).

I just put them into a plastic electrical box, put a plastic cover plate
over them. No problem. Even a shallow box is deep enough. Did you
just not want to use plastic?

Oh, and I'm considering splitting the outlet such that 1/2 is always on,
the other half runs from the timer.

sdb
--
Wanted: Omnibook 800 & accessories, cheap, working or not
sdbuse1 on mailhost bigfoot.com

 

[Andrew Holme]

Skeleton Man wrote:

From the minute it's turned on to the minute you switch it off it
interferes (doesn't matter if it's transmitting or not)

The power lead could be radiating; you might one or more supression
techniques (LC filter / screening / toroidal balun / re-routing /
shortening) on that.

So put the LC filter on the 2-way power supply and the radio, or just
the 2-way ?

It's trial and error, I'm afraid. Try the easier things first.

How do I calculate input/output impedance for the filter ? (so I can
find a table listing component values)

Actually, it's not that critical. We're not matching a 50 ohm signal. I
might try a PI-network with (say) 100n capacitors to ground and (say) 100uH
in series. The capacitor leads need to be short.

 

[Anthony Fremont]

"Danny T" <danny@nospam.oops> wrote in message
news:41d7c20d$0$14580$ed2619ec@ptn-nntp-reader01.plus.net...

Anthony Fremont wrote:

It looks ok to me. I assume you have MCLR disabled and are using
the
internal oscillator.

Yep! (When I can figure out how to stop the programmer going nuts when
I
disable MCLR! - If not, I guess I just connect the MCLR pin to the PIC
Vdd pin?)

Yes, you can usually tie it directly to the +5V.

Going back to the regulators...:


http://www.rapidelectronics.co.uk/rkmain.asp?PAGEID=20671&CTL_CAT_CODE=30416

That's determined by how much current you need to draw, how much
power
the regulator is going to have to dissipate (as heat) dropping the
voltage to the output level and how much margin the regulator has to
work with (i.e. how much greater the input voltage is than the
output
voltage). The LM2940CT looks pretty good for you for all around
experimentation if you want to supply allot of current, but the
LP2950CZ
should work ok in your circuit (as long as it is not trying to drive
the
motors too). It is limited to 160mA output.

So, would I be right in thinking that 2x LM2940CT-5.0 would drop 6V to
around 5V?

Why 2x?

I want to drive 2x3V motors, but it seems the LM2940CT-5.0 has a
minimum
input of 5.45 (to drop to around 5V). Motor specs say:

No load current 0.34A max.
Rated load current 1.07A max.

But none of the low dropout regulators seem to fit... Was just looking
at fixed voltage regulators, but the only one that'll allow a high
enough current is an output of 5V, still too high for my motors :-(


http://www.rapidelectronics.co.uk/rkmain.asp?PAGEID=80010&CTL_CAT_CODE=30414&STK_PROD_CODE=M29655&XPAGENO=1

Any suggestions?

Don't use a regulator to power your motors. You could use a bunch of
diodes, you could tap power from the middle of the battery pack, you
could put the motors in series, or you could PWM the motors directly
with the +6V. There are other ways, but I'd probably go with center
tapping the PS (battery pack) or better yet using a different PS
altogether for the motors (helps prevent noise in the PICs PS).

 

[Andrew Holme]

Danny T wrote:

Andrew Holme wrote:

The 1N4148 is only rated for a maximum forward current of 300mA.
Use the 1N4001.

That's 1A, correct?

One set of my motors (much higher RPM than the other) have a max
current of 1.07A... If I need to use them, am I still ok with these?
What about if I use a lower voltage than the max? Or should I find
something rated higher just to be safe?

The 1N4001 is fine for 1.07A as long as you only run one motor at a time.
You should find something heftier, or use seperate dropper chains, if you
need to run two 1A motors at once. The .07 is negligible.

(It's not a life support system )

If I destroy up (a diode, resistor, MOSFET etc.), is it easy to
detect? Will they stop conducting, or could they potentially blow
other things along the way (eg. if a resistor stopped resisting!!!)

Resistors can go short circuit if you subject them to enough abuse, but they
tend to smoke and become discoloured in the process - which is a bit of a
giveaway. You can test diodes with your multimeter. The best way to tests
the MOSFETS would be in-circuit: disconnect the gate; connect a 1M resistor
from gate to ground; lick your fingers; put a wet finger on the gate; put
the other finger on +5V or GND: you should be able to switch the motor on
and off.

BTW some MOSFET gates are static sensitive - observe handling precautions.

I forgot to mention - on rapidelectronics - you want a MOSFET marked * for
"Logic level device with optimised design for 5V drive"

 

[Danny T]

John Popelish wrote:

Keep in mind that motors do not have to run at exactly the specified
voltage, but that the speed will be roughly proportional to the
voltage (torque held constant) and the torque will be roughly
proportional to the current (speed held constant). Picking the right
motor is a lot like picking the right gear in a car that matches the
motor (speed-torque and efficiency curves) to the driving conditions
(speed, climb, weight carried, wind, acceleration needed, etc.)

Yep. Either will do for now, but until I put wheels on carpet, I won't
know if the weedy one has enough power to move it. Got some cogs (a worm
thing?), so I don't imagine it'll be a problem - can sacrifice speed for
mobavility !

--
Danny

 

[John Popelish]

Danny T wrote:

John Popelish wrote:

The source lead. The caps connect between the positive and negative
supply points for the motor and its driver transistor (as close as
possible to those points, too). When the drive transistor turns off
or on, suddenly, a wave of current would otherwise travel all the way
back to the battery, bouncing every circuit connected to it.

Sorry, I thought you meant both ends connected to the leads you
specified, but from reading Andrew Holme's post, I gathered that one end
connects to the join from the MOSFETs to the motors, and the other end
to ground - is this correct?

No. The positive end of the electrolytic and one end of the film cap
connects to the positive lead of the motor. The negative end of the
electrolytic and the other end of the film capacitor connect ot the
source lead (grounded lead) of the mosfet driving the motor. This
acts as a small, 3 volt battery as close as possible to the motor.

I don't quite understand the need for two *different* capacitors - why
would one not do?

The electrolytic is good at dumping a big current for a long time, but
it has the aluminum wound up inside it, so that there is a bit of
inductance in series with the capacitance that doesn't allow it to
have this current change in an instant. The smaller, low inductance
capacitor supplies the current during this brief time.

Since you have two motors and two motor drivers, there should probably
be a set o capacitors for each (especially if you use a separate
voltage regulator for each motor), unless the two mosfets are right
together and the positive leads to the motor are also very connected
directly together.

--
John Popelish

 

[Danny T]

Danny T wrote:
<snip>

Yet more questions.. ;P

This comes from a book - "INSECTRONICS - Build Your Own Walking Robot"
by Karl Williams. I've no plan on walking robots, but it has IR sensors
and stuff in it, so it's a good read. Anyway, one of the circuits looks
like this:

http://dantup.me.uk/tmp/circuit.jpg

I noticed a few things...

1. MCLR is tied to Vdd with a 4.7K resistor. I had them connected
directly. Since MCLR probably doesn't draw much current, I don't
understand what the resistor would do... Anyone?

2. RB1 and RB2 have a 1K resistor, then what looks like two diodes. If
these are unused, are the diodes needed? If they're supposed to be LEDs,
1K seems high - I calculated my two sets of LEDs as needing 120Ohms
and 160Ohms?

3. The speaker ties to the same "ground" as the main +5V supply, but it
seems to have its own +9V supply. Surely each should return to it's own
power source?!

4. RA2 has a jumped, and gets tied to +5V or ground, via a 1k resistor.
I've been using 10k - how important is this value?

Sorry for asking silly questions, but I find it's the best way to learn! )

--
Danny

 

[Danny T]

Andrew Holme wrote:

Good news (for me!)... I just got my first breadboard circuit working! I
think my problems had all been down to MCLR! I just created the circuit
you've been helping with here, but without the motors (and without the
Vdd->Vss cap, since I don't have them yet!). It just flashes two sets of
LEDs on and off, and has the unused pins (and inputs I don't yet have
switches for) tied to ground with resistors.

W00t! That's the hard part - now I can get programming world peace
instead of just LEDs! =)

1. MCLR is tied to Vdd with a 4.7K resistor. I had them connected
directly. Since MCLR probably doesn't draw much current, I don't
understand what the resistor would do... Anyone?

This is an obsolete practice. Pull-ups were required for the original 7400
series TTL logic family back in the 1970s but they're not necessary with
modern CMOS. You can tie CMOS inputs directly to Vdd.

I just removed the 4.7K resistor on my breadboard, and it still works
the same. I'll ignore this in future

The (small) double arrows at 45 degrees identify them as LEDs. They will
glow dimmly with 1k. Perhaps the designer was trying to save power?

I thought they where LEDs, but thought I'd cover all bases
Ironically, the lowest resistor I have here is 1K, so I've had to use
them for my test, and the LEDs glow fine - I guess there's no point
giving them more power if they don't need to be brighter
(or maybe he was using his dads old resistor box too!)

3. The speaker ties to the same "ground" as the main +5V supply, but
it seems to have its own +9V supply. Surely each should return to
it's own power source?!

The grounds are connected; note the earth symbols:

|
|
-------
-----
---
-

I see. Is there any advantage to connecting all the ground together from
different sources to just having them totally seperate? Is it just to
make wiring easier, since any ground will do? Would this cause any extra
noise from things like motors?

4. RA2 has a jumped, and gets tied to +5V or ground, via a 1k
resistor. I've been using 10k - how important is this value?

The value is not critical; 100 ohms or 100k would also work.

Ok, so what *exactly* is the resistor doing? What does it do when it's
given say 0, 3, 5, 7 volts?

The resistor would be un-necessary for a CMOS input, but is a wise
precaution in case the software ever programs the I/O port as an output.

I see. Does the same hold for my circuit? I've got +5V, connected to a
resistor, then to both the input pin and a switch. If I *know* my chip
is an input (eg., I've tested it *with* the resistor), is it safe to remove?

The same is not, apparently, done on JP7; is this an output?

Don't know, it's not explained, and the assembly's pretty long... I'll
just ignore this for now
--
Danny

 

[Robert Monsen]

Danny T wrote:

Andrew Holme wrote:

Good news (for me!)... I just got my first breadboard circuit working! I
think my problems had all been down to MCLR! I just created the circuit
you've been helping with here, but without the motors (and without the
Vdd->Vss cap, since I don't have them yet!). It just flashes two sets of
LEDs on and off, and has the unused pins (and inputs I don't yet have
switches for) tied to ground with resistors.

W00t! That's the hard part - now I can get programming world peace
instead of just LEDs! =)


1. MCLR is tied to Vdd with a 4.7K resistor. I had them connected
directly. Since MCLR probably doesn't draw much current, I don't
understand what the resistor would do... Anyone?


This is an obsolete practice. Pull-ups were required for the original
7400
series TTL logic family back in the 1970s but they're not necessary with
modern CMOS. You can tie CMOS inputs directly to Vdd.


I just removed the 4.7K resistor on my breadboard, and it still works
the same. I'll ignore this in future

I just looked at the datasheet for the 16F676, and it specifies a
resistor of at least 1k, along with an optional cap of 0.1uF to ground.
This is on pg 58 of the 16F630/16F676 datasheet.

Also, note that MCLR can be used to avoid problems when the voltage
comes up too slowly. Microchip sells a part specifically for this (the
MCP100 series, if memory serves) that will keep MCLR low until the
voltage comes up enough for the system to run. You can also build a
circuit like this fairly easily, or just ignore it and tie it to Vdd if
you aren't worried about it. However, MCLR problems seem to be endemic
to the microchip product line for some reason.

The (small) double arrows at 45 degrees identify them as LEDs. They will
glow dimmly with 1k. Perhaps the designer was trying to save power?


I thought they where LEDs, but thought I'd cover all bases
Ironically, the lowest resistor I have here is 1K, so I've had to use
them for my test, and the LEDs glow fine - I guess there's no point
giving them more power if they don't need to be brighter
(or maybe he was using his dads old resistor box too!)


3. The speaker ties to the same "ground" as the main +5V supply, but
it seems to have its own +9V supply. Surely each should return to
it's own power source?!


The grounds are connected; note the earth symbols:

|
|
-------
-----
---
-


I see. Is there any advantage to connecting all the ground together from
different sources to just having them totally seperate? Is it just to
make wiring easier, since any ground will do? Would this cause any extra
noise from things like motors?

Ground is the common reference point in your circuit. Without it, you
can't connect up the parts of your circuit. This is because voltage is
not an absolute measure, it's a relative measure. Thus, when you signal
from one part of your circuit to another part using voltage you must
reference that voltage signal to something. That something is ground.

Note, however, that ground isn't always the same. Wires have a little
resistance and inductance, and so the more current that flows over them,
and the more it changes abruptly (as in motors), the more voltage will
be across them. Consequently, grounds that have lots of current can be
different than grounds that have only a little current. Just something
to keep in mind.

4. RA2 has a jumped, and gets tied to +5V or ground, via a 1k
resistor. I've been using 10k - how important is this value?


The value is not critical; 100 ohms or 100k would also work.

Actually, many microchip parts have internal "weak pullup resistors",
which can be turned on and of individually for port pins. They are 10k.
Look at the datasheet for your part.

I was just bitten by this, in that I forgot about the internal pullups,
and wondered why my 100k resistor wasn't pulling the input to ground.
Turning off the pullups fixed the problem.

Ok, so what *exactly* is the resistor doing? What does it do when it's
given say 0, 3, 5, 7 volts?


The resistor would be un-necessary for a CMOS input, but is a wise
precaution in case the software ever programs the I/O port as an output.


I see. Does the same hold for my circuit? I've got +5V, connected to a
resistor, then to both the input pin and a switch. If I *know* my chip
is an input (eg., I've tested it *with* the resistor), is it safe to
remove?

The initial value for parts from reset is to be an input, I believe.
Unless you explicitly change this, they will never be an output.
However, you are not taking into account possible software errors that
may creep in at a later date. Prudence suggests that you provide for
this possibility by using a resistor.

The same is not, apparently, done on JP7; is this an output?


Don't know, it's not explained, and the assembly's pretty long... I'll
just ignore this for now

--
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.

 

[Bob]

<j2israel@hotmail.com> wrote in message
news:1104989021.307182.192850@c13g2000cwb.googlegroups.com...

Hello all.

I have some questions about how the "typical" phone line switch network
works (being in the US).

This is what I understand:
When two people (two phones/nodes) talk using standard hard wired or
cordless phones it may appear to them that they are having a continous
conversation, but they really are not. The phone network is a switching
network where multiple people (at multiple nodes) will talk and there
voice signals will be sent over the phone lines for a given time and
then not while another two nodes are connected. This is a good example
of TDM (time division multiplexing).

I have two questions:
1) Since people can hear audio signals around the bandwidth of 200Hz -
20kHz and most people speak with an audio signal frequency between 1kHz
- 2kHz. What is the sampling frequency that the phone lines switch at?
Would it be 44.1Khz? (Somewhat satisfying Shannon's Sampling Theorem).

2) From question (1) it seems to me that if this sampling frequency is
static then that puts a limit as to how many people (nodes) can be
connected to the phone line network. If there are more nodes than the
sampling frequency can handle then the "switched off" times for nodes
will be too great and there will be noticeable distortion.
If the sampling frequency is not static and is dynamic, what control
system(s) "sees" how many nodes are trying to connect so that the
sampling frequency can be adjusted accordingly.
Thanks for your time. I again am a novice.

jacobdav

The public switched telephone network (PSTN) samples each telephone 8000
times per second. The associate equipment's high-pass and anti-aliasing
filters result in a net bandpass of 300Hz through 3400Hz. Each digital
sample is 8 bits, but the weight of each digital level is not linear. The
"step size" of each level gets closer together as the sampled analog signal
is smaller (in magnitude). In the USA this is called ulaw (pronounce mu
law). In Europe they use alaw. Both coding schemes' goal is to provide
constant signal-to-noise ratio -- as a function of signal level (i.e., as
the signal level gets lower then the quantization noise gets lower, too).

This 8ksps @ 8bps results in a 64Kbps voice channel. This is commonly
referred to as a DS0 channel. An OC192 fiber interface (roughly 10Gbps)
carries 129,024 DS0's. That's a lot of phone calls on two strands of glass.

The sampling frequency/sample width was a compromise to maximize number of
phone calls (for a given interface rate) and to reproduce acceptable voice
quality.

Bob

 

[Dan Dunphy]

Top post.
This has nothing to do with newtons, a physical unit of force.

Energy E = 1/2 *C*V^2 . In the MKS system "joules".
A joule is 1 watt-second

On 4 Jan 2005 12:26:23 -0800, zooeb@libero.it (zooeb) wrote:

I think electrical matter is very hard to grab, because current,
voltage & C. are invisible. Even after years of practice I have some
doubts about it. Here they are (someone): 1)voltage mean how many
Newton every Coulomb is able to "put out". But, what is the difference
between 1 Coulomb that has 100 Newton (for example) in it (ready to
put out) and 1 Coulomb that has 200 Newton (for example) in it (ready
to put out); in particolar what does it change in phase of generation
of voltage? Why the second quantity of charge has more power?
2)imagine a voltage generator empty (I mean it generate voltage, but
there is no load attached to) so that current is zero, then imagine I
prolong one of the two terminal, connecting to it a piece of wire of
relevant lenght regard to the lenght of generator terminal. Just
connected it; is there an electric current (even for a little while)
which flow into the wire? I think yes, there is a current, because
electric charges concentred in the terminal have the possibility to
expand along the new wire. 3)OK, now imagine always the same situation
of point number 2; and imagine of disconnecting the wire: all the
electric charge which there were in it remains or falls down? 4) All
generators I know behave similar to voltage generator: does it exist a
similar current generator without electronic device (transistor,
diode, ...) in it? 5) I'm thinking a way of imaging current, voltage,
resistance, impedence, capacitance, inductance, electric field,
magnetic field, electromagnetic field using duality with other
matters. The easiest way is to think voltage like water pressure, but
using hydraulic duality I think you are not able to introduce the
concept of impedence, capacitance, electromagnetic fields, .... Have
you a piece of advice about it? 6) Thank you very much, bye.

 

[Danny T]

Thanks everyone - picked my bits up today (postman had claimed he
couldn't deliver them and left them at the sorting office!), and put it
together. All works brilliantly!

I tried yesterday with some odd components lying around, but only had an
NPN transistor, no MOSFET, which resulted in my motor going fast and
slow, instead of fast and off!!

Now I just need wheels and a chassis!

Ta,

--
Danny

 

[Matt J. McCullar]

Not dental, but a friend of mine claimed he once heard a radio station over
a flashlight. This happened back in the 1970s and he said he'd go into the
kitchen late at night for a snack, and in the dead quiet darkness he could
barely hear someone talking. Very strange; he didn't believe in ghosts but
it took him a while to find where the voices were coming from: a flashlight
held onto the side of the fridge by a magnet.

He didn't say what he did with the flashlight, as this was many years ago,
but it would be interesting to dissect it today and see what was causing it.
Perphaps some battery acid was acting as a rectifier between a battery
terminal and a big spring. Once he had satisfied himself as to the source,
he said he just left the flashlight alone and let it freak out his relatives
who thought the kitchen was haunted.

My father told me he once heard a story of someone claiming to hear a radio
station in her kitchen oven. This was the old convection oven, the kind
built into the wall. He said it probably had something to do with old
grease and other food-related crud building up against some metal contacts
inside the oven.

I remember when I was a kid, picking up WBAP-820 AM radio very clearly over
my little 3" reel-to-reel tape recorder speaker whenever I touched my finger
to the terminals of the playback head. I guess my body was acting like a
capacitor/antenna. WBAP is a big powerhouse and at the time I lived in the
same city (Fort Worth).

 

[Dominic-Luc Webb]

On Sat, 8 Jan 2005, Danny T wrote:

I tried yesterday with some odd components lying around, but only had an
NPN transistor, no MOSFET, which resulted in my motor going fast and
slow, instead of fast and off!!
--
Danny

Danny, it will be great to see how this progresses. I am interested in
the reason why the effect on speed is occurring. It sounds like a
problem I am encountering with the 2N3055 NPN power transistor. I do
not find conditions under which it actually shuts off and I do not
understand why. I do know the basic calculation strategies using beta
to determine Ib from a pre-determined Ic, etc. It is maybe noteworthy
that some of these inductor circuits (speakers, transformers, motors,
etc) have variable current draw, so this must mean that Ic will vary.
If one clamps the Vbe and Ib with a fixed voltage and resistance,
respectively, I presume that beta changes. I am quite curious how each
of these parameters effects the others. At least in the case of the
2N3055, it has both low frequency 0.8 MHz, and I suspect slow rise and
fall times and also relatively low beta (between 20 and 70). I suspect
this obligates a very narrow dynamic range. Compare, for instance to a
BD139 with a beta around 160 and frequency of 250 Mhz. Very different.
I suspect the 2N3055 is leaky, but I lack good proof. It came as a
surprise that I could run such inductor circuits a lot better with much
lower power NPNs than the 2N3055. One of the most reliable was a BF658,
which is small signal 1 Watt, Ic 0.12 Amp.

It is also frustrating that the specifications often do not tell what
kind of NPN transistor. I have seen the 2N3055 called a Darlington,
and I have seen internal schematics that clearly show that it is not.
I suspect the latter, and nonetheless, this transistor has not been
real popular with me, despite its massive power rating. I think it is
the low beta (and leakage?) that has made working with it a challenge.


Dominic

 

[John Popelish]

Dominic-Luc Webb wrote:

It is also frustrating that the specifications often do not tell what
kind of NPN transistor. I have seen the 2N3055 called a Darlington,
and I have seen internal schematics that clearly show that it is not.

It is always a good idea to review the data sheet if you can find one:
http://www.onsemi.com/pub/Collateral/2N3055-D.PDF

--
John Popelish