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'[EE]: Winding inductor for 2 trans. LED blinker'
2002\10\19@202746 by William Chops Westfield

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   Why not have a look at Clive Mitchell's version: his uses a single
   transistor and he includes pictures of how to use a ferrite bead to make
   the inductor.  Have a look at
   <http://www.emanator.demon.co.uk/bigclive/joule.htm>

This circuit came under discussion on the yahoo BEAM group recently, and I
did a bunch of experiments with inductors found and/or wound on all sorts of
random cores, including small ferrite toroids and filter inductors from SM
power supplies.  Look for messages with "Joule" in the header - I even
posted pictures.  (Since this "transformer" design calls for only about 20
turns (bifilar), it rather sapped by interest in homemade "simple"
inductors...)

BillW

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2002\10\21@211346 by William Chops Westfield

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Can a simple oscillator circuit (555, coupled inverters, etc) be induced
to use an inductor instead of a capacitor as the energy storage element?

BillW

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2002\10\23@141623 by Peter L. Peres

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On Mon, 21 Oct 2002, William Chops Westfield wrote:

*>Can a simple oscillator circuit (555, coupled inverters, etc) be induced
*>to use an inductor instead of a capacitor as the energy storage element?

Coupled gates oscillators will work with an inductor. The inductor should
shunt a gate afair (instead of a feedback resistor).

Peter

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2002\10\23@175441 by Russell McMahon

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> *>Can a simple oscillator circuit (555, coupled inverters, etc) be induced
> *>to use an inductor instead of a capacitor as the energy storage element?
>
> Coupled gates oscillators will work with an inductor. The inductor should
> shunt a gate afair (instead of a feedback resistor).

Interestingly (perhaps) I've just used a gate shunting inductor in a crystal
oscillator to "solve" an otherwise intractable problem. The entire presently
available production (latest date code) of a particular model of non-PIC
microprocessor has startup problems in certain circumstances. Everything
else I tried failed to adequately improve the results. Adding a 22 uH
inductor across the crystal made a very substantial difference. While an
inductor in this location notionally "cancels" an equivalent amount of
capacitive reactance in the crystal at the operating frequency, in practice
the results are far more extensive than might be expected. Changing the two
capacitors from either leg of the crystal to ground in various ways produces
interesting results. It is possible (not recommended!) to obtain oscillation
output outside Vdd and ground (due to LC tank) and to have the oscillator
input waveform of higher amplitude than the output.

The inductor used is one of the small barbell cored ones such as Roman is
using in his Black Converter and has a dc resistance of about 1 ohm. Smaller
and larger values work but 22 uH seems optimum for my requirement. The
inductive reactance is only about 1,100 ohms at crystal resonance.



               Russell McMahon

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2002\10\23@181116 by Jim

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I'm curious - what brand/manufacturer of crystal?

Have you had an opportunity to 'characterize' the crystal
(measure it's parameters) on an xtal test set?

(Perhaps a lower-than-average-Q 'rock' in conjuction
with an oscillator whose gain is in the low end of the
acceptable spectrum is the overall problem ...)

RF Jim

{Original Message removed}

2002\10\23@192342 by Russell McMahon

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> I'm curious - what brand/manufacturer of crystal?
>
> Have you had an opportunity to 'characterize' the crystal
> (measure it's parameters) on an xtal test set?
>
> (Perhaps a lower-than-average-Q 'rock' in conjuction
>  with an oscillator whose gain is in the low end of the
>  acceptable spectrum is the overall problem ...)

A change in crystal characteristics was one of the things high on my list of
suspect candidates.
Unfortunately, it was as I said
   > > an otherwise intractable problem.
ie I had tried changing everything else in sight (and a few things not in
sight) including the crystal. The change occurred with processor date code
change. ALL devices prior to this date code work 100%. About 50% with new
date code fail. Manufacturers (in Taiwan) assure me that the crystal type,
manufacturer etc has not been changed. I was sent 11 sample boards with the
fault. Changing the crystal to ones available locally (in New Zealand) does
not alter result.

The problem APPEARS to be related to the processors sensitivity to latch up
during power on if certain voltages are present on pins when Vdd is applied
with certain (or uncertain :-) ) rise times. Suffice it to say that
everything I am doing is inside datasheet spec but processor does not always
start (whic is ouitside datasheet spec :-) ).

Even clamping all (sensible) pins to Vdd with Schottky diodes does not
prevent maloperation.
Once in the errant mode the oscillator does not start and the processor will
not return to normal until Vdd drops to below about 0.1v. This can take some
10's of seconfds in a normal circuit as once silicon junctions stop being
biased on current draw is due almost only to purely passive loads.

The 22uH made all but one of the samples work OK - the last may have other
problems or be an especially bad example.



       Russell McMahon

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2002\10\23@212502 by Jim

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Sounds like the phase-gain characteristics of the
active element comprising the on-board osc
have changed ... do you have a means to test this?

... simple feedback resistor, inject a signal and
observe the 'phase-gain relationship' at several
different frequencies ...

If the placement of the inductor was across the
'inverter' that comprises the active osc device,
you have effectively shunted the DC (and low
freq. gain) gain of that stage ...

RF Jim

{Original Message removed}

2002\10\23@224056 by Russell McMahon

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re "Brand X" Microprocessor startup problems.

> Sounds like the phase-gain characteristics of the
> active element comprising the on-board osc
> have changed ... do you have a means to test this?
>
> ... simple feedback resistor, inject a signal and
> observe the 'phase-gain relationship' at several
> different frequencies ...
>

I have no formal test equipment to test this but could devise something if
it seemed liable to help.
However,

   The Taiwanese manufacturer has tried "all the usual" tricks to make the
oscillator start properly. The best solution they found was a 1M across the
oscillator pins and a 56r in series with the crystal. The latter is lower
than is usually suggested and the 1M  is typical. As is usually the case,
the processor has an internal feedback resistor which is supposed to be
adequate.

      Microprocessor oscillators are meant to oscillate. While the best
capacitors for the task need to be chosen and while these will be affected
by crystal requisite load capacitance and while crystal "activity" and other
arcane parameters can and do change with batch, the oscillators are meant to
oscillate. With suitable experiment (or calculation if suitable instruments
are used) a NORMAL solution should work reliably. This processor doesn't do
what it should. As I noted in my original comment, this is in "certain
circumstances". The application in question has "interesting" power supply
rise characteristics for technically good and sufficient reasons. (These
could be altered with suitable cost and effort). These contribute to the
problem. The spec sheet places no limitations on supply rise times. A
properly designed internal reset circuit will allow a processor to start up
cleanly and reliably regardless of supply behaviour. As the processor in
question has NO external rest line it is essential that the internal
circuitry is able to handle anything it encounters. [[ Another version of
this family had a similar problem about 2 years ago when, in one batch only,
if the supply was raised VERY slowly, the oscillator would start but the
processor would not. Very repeatable and limited to one date coda. I suspect
that a similar but not identical problem is occurring here.]]

As noted initially, the problem appears to be a form of latchup and is very
possibly based on voltages (and their impedance*) at various pins during
restart. Most "bad" processors will start when power is first applied and
not subsequently unless a suitable delay is allowed to replicate initial
conditions.

My aim was not to analyse the problem I have (but yer all welcome to IF you
can fix it more cheaply than by using a 22 uH inductor) but to note the fact
that such an arrangement may have its uses as we were talking about RL based
oscillators (which this isn't an example of :-) . .

> If the placement of the inductor was across the
> 'inverter' that comprises the active osc device,
> you have effectively shunted the DC (and low
> freq. gain) gain of that stage ...

Indeed! The 1 ohm inductor resistance will do this quite well :-) In the
PCBs that I have been sent there is a 56r is series with the crystal and the
22 uH is across the crystal so this provides a small dc component across the
oscillator proper. However, even with this 56r shorted out )so 1r coil
across oscillator pins) the results were essentially identical. (A series r
is usually used to reduce oscillator signal magnitude with a very active
crystal to prevent crystal damage. In this case the value has been selected
by trial by the Taiwanese to get best startup results.)


   Russell McMahon

* - the circuit includes a Sigma-Delta converter which uses a 1uF capacitor
which is directly from a processor pin to ground. As this could have been
providing a source of low impedance dc at restart I tried replacing it with
a much smaller value cap during testing - no change in results.

Similarly, connecting all pins to Vdd with Schottky diodes produces a most
interesting looking result but no practical improvement in performance.

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2002\10\23@225548 by Jim

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 "Microprocessor oscillators are meant to oscillate"

Spare us the verbage and perform the test on the osc
stage as "there is no substitute for 'the facts'".

(This is not debate class - this is "practical engineering
101"!)

This may or may *not* lead to a solution - but your alternative
is 'a few well-placed shots in the dark' (you look to have
found a work-aound in the mean-time, this, of course, is good).

*Real* problem solution calls for UNDERSTANDING each component
in the system - and the osc element is an important part of
this ... the next stage to all this GIVEN component values
and parameters would be to slap together a simple model in
SPICE and see how that flies. This, of course, would not take
into consideration ANY 'funnies' the 'front end' (THOSE
who fabricated those devices on a wafer prior to their being
cut up and mounted as 'die' in a package) fabrication process
may have 'instilled' (been there - seen that) ...

RF Jim

{Original Message removed}

2002\10\23@230031 by Jim

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 "I have no formal test equipment to test this "

Dual-channel/trace-scope and a sine wave gen good to ?? 5 or 10 MHz?

We would look at phase change and amplitude (gain) input to output.

*If* the gain dies off prematurely or the phase shift becomes
excessive - we have found an area to look at more closely
(PENDING there being no semiconductor fabrication/doping errors
by the FE (front end)!!!).

RF Jim

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2002\10\24@084639 by Russell McMahon

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2 related messages mixed together here:

>>   "I have no formal test equipment to test this "

> Dual-channel/trace-scope and a sine wave gen good to ?? 5 or 10 MHz?

I assumed you were talking about specific equipment. As I noted, > "I could
devise something if it it seemed liable to help". Scopes, sig gen etc
readily available. The question is the chance that this would produce useful
results. (I have since done just this as every straw is worth clutching at,
but, if anything, the amplifier in the "bad" processors is slightly better
than that in a good one.)

>>  "Microprocessor oscillators are meant to oscillate"

> Spare us the verbage and perform the test on the osc
> stage as "there is no substitute for 'the facts'".

If you think that's verbiage (aka verbage) then you just may have missed my
point, or perhaps not read through everything I wrote?
The point was that one hopes not to have to redesign one's microprocessor
after one buys it, or have it change characteristics in a major and
arbitrary manner without notification of any sort (as happened here), or
find that it does not respond to ANY of the reasonable & standard efforts
one makes to make it start oscillating properly in a circuit which falls
within the spec sheet spec. Having to place an inductor across the crystal
is not an expedient one might reasonably expect to have to take. As I noted,
there is strong evidence that the ultimate problem is some form of latchup
rather than just a badly behaved oscillator in the normal sense.

> (This is not debate class - this is "practical engineering
> 101"!)

Practical engineering 101 I can handle. Alas this is more akin to arcane
engineering 490 (with extra credit for not meeting spec sheet criteria and
requiring non standard work arounds.)

> This may or may *not* lead to a solution - but your alternative
> is 'a few well-placed shots in the dark' (you look to have
>found a work-aound in the mean-time, this, of course, is good).

Practical engineering 101 (also 220 & 370) is about gaining experience
required to be able to have one's "well placed shots" land somewhere near
the target (as I know you know). Certainly "having adequate test equipment
360" and "stopping and thinking what may actually be wrong 420" (post grad)
have their place.

> *Real* problem solution calls for UNDERSTANDING each component
> in the system - and the osc element is an important part of
> this ... the next stage to all this GIVEN component values
> and parameters would be to slap together a simple model in
> SPICE and see how that flies. This, of course, would not take
> into consideration ANY 'funnies' the 'front end' (THOSE
> who fabricated those devices on a wafer prior to their being
> cut up and mounted as 'die' in a package) fabrication process
> may have 'instilled' (been there - seen that) ...

Agree with all that more or less BUT it is my considered opinion that the
problem is the worst case one you mention - somebody has done something
arcane and isn't fessing up. MOST customers will not be affected MOST of the
time so they will probably get away with it. It is very very clear that
something changed radically along with a date code. When the manufacturer
denies that anything changed at all rather than explaining what has changed
and why so that you can try and work with it, then the situation is
"difficult".

I have the easy long term solution though! It's almost certain that I will
never design this manufacturer's products into anything again. We'll wait
and see how it works out - they may yet redeem themselves somewhat.



       Russell McMahon
.

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2002\10\24@143605 by Roman Black

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Russell McMahon wrote:

> The inductor used is one of the small barbell cored ones..


Hi Russell, I think you mean "dumbell" ie, short
with thick disc ends. :o)

I'm curious as these are normally larger and
significantly more expensive than the RF choke
type, surely at 22uH the choke type would be
smaller and much cheaper? I've seen really small
dumbell types but they are still about 5mm diam
ends which is still bigger and (I presume) more
expensive than the tiny choke type.
-Roman

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2002\10\24@194553 by Russell McMahon

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part 1 996 bytes content-type:text/plain; (decoded 7bit)

> > The inductor used is one of the small barbell cored ones..

> Hi Russell, I think you mean "dumbell" ie, short
> with thick disc ends. :o)

Barbell = = Dumbell
(probably different words in use in different countries)

> I'm curious as these are normally larger and
> significantly more expensive than the RF choke
> type, surely at 22uH the choke type would be
> smaller and much cheaper? I've seen really small
> dumbell types but they are still about 5mm diam
> ends which is still bigger and (I presume) more
> expensive than the tiny choke type.

These are very small - about 3mm diameter and 5mm length with a small
ferrite "drum" inside with a slot where the wire is wound. We may be talking
about the same component.

Photo attached of  a 22uH choke with plastic outer removed - plus ballpoint
tip for size comparison.

I suspect these are about as cheap as anything available.


       Russell


part 2 3584 bytes content-type:image/jpeg; (decode)


part 3 154 bytes
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2002\10\24@204238 by Tom Messenger

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Note the similarity of Russell's photo to a bobbin that holds thread.
Thus, they are frequently called "bobbin-wound" inductors.

At 12:40 PM 10/25/02 +1300, you wrote:
>> > The inductor used is one of the small barbell cored ones..
>
>> Hi Russell, I think you mean "dumbell" ie, short
>> with thick disc ends. :o)
>
>Barbell = = Dumbell
>(probably different words in use in different countries)
>

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2002\10\25@074328 by Olin Lathrop

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> Barbell = = Dumbell
> (probably different words in use in different countries)

A barbell is something you excercise with.  A dumbell is someone who asks
what a barbell is <g>.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\10\25@143942 by Roman Black

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Russell McMahon wrote:

> > Hi Russell, I think you mean "dumbell" ie, short
> > with thick disc ends. :o)
>
> Barbell = = Dumbell
> (probably different words in use in different countries)

Just to be a "Gym Olin" a barbell is a long one
you use in both hands and dumbell is a short stumpy
one for one hand. <grin>
But I stand corrected that the most common description
of this ferrite core is probably "bobbin core" as
Tom pointed out. :o)

> These are very small - about 3mm diameter and 5mm length with a small
> ferrite "drum" inside with a slot where the wire is wound. We may be talking
> about the same component.
>
> Photo attached of  a 22uH choke with plastic outer removed - plus ballpoint
> tip for size comparison.

Nice picture! Wow they get smaller all the time.
3mm diameter ends hey? The ones we have been buying
from Farnell have gone from a 10mm size of the
original catalogue stock and are now 8mm size with
*better* performance. Ferrite properties are
really advancing in leaps and bounds. :o)
-Roman

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2002\10\26@212402 by Charles Craft

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http://www.aade.com/lcmeter.htm

I ordered the kit on Tuesday and it was waiting at the post office when I got back into town on Friday.

Took me a little over an hour to assemble - would have been less without interruptions from the wife about other chores to be done.

Other than getting the components to lay down under the LCD it was a piece of cake and fun to put together.

Attached a battery, powered it on and got text on the display. :-)

I have access to a lot of electronic surplus places here in Minneapolis where parts are cheap but wonder if things are in the right bins - especially inductors. This thing will come in handy when shopping for parts.

UNIX and network mgmt is my day gig; PICing around is just a hobby so this fits a nice price/function range.

bubba




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2002\10\27@051440 by Roman Black

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Charles Craft wrote:

> http://www.aade.com/lcmeter.htm
>
> I ordered the kit on Tuesday
>
> Took me a little over an hour to assemble


Hi, how does it go with very small inductors and
zero inductance?? Does it read zero uH if you short
the terminals with a straight wire, and will it
read a few turns of wire, ie 1uH etc values reliably
without drift and the same each time you read it?

Many digital inductance meters are optimised for
the typical 1mH values and are less than perfect
with small values. The write up on his web page
sounds good but it would be nice to hear your results.
:o)
-Roman

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2002\10\27@114508 by Jim

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Roman, the secret to the AADE LC Meter would seem
to be it's oscillator circuit (described below) - that,
and the LC Meter's built-in 'calibration' cycle it goes
though (all controlled by a PIC of course!).

+ + + + + + + + + + + + + + + + + + + + + + + +

Circuit Description - The Oscillator

The key to L/C Meter IIB's operation is the oscillator circuit of FIGURE 1.

http://my.integritynet.com.au/purdic/lc-meter-project.htm#circuit-osc

The LM311 is a voltage comparator. When power is applied, the voltage at pin
2 is 2.5 volts causing the output to be at a level of 5 volts. This charges
capacitor C4 through resistor R4 until the voltage at pin 3 equals 2.5
volts. As it reaches 2.5 volts the output switches to a low level inducing a
transient into the tank circuit composed of L1 and C1.

The transient causes the turned circuit to ring at it's resonant frequency.
The ringing causes a square wave at the resonant frequency to appear at the
output of the voltage comparitor. The square wave is coupled back to the
tuned circuit through R3 and C3 sustaining oscillation.

For the nominal values of L1 (68 uH) and C1 (680 pF) an increase in L of 1
nH (.001 uH) or an increase in C of .01 pF produces a frequency change of
slightly more than 5 Hz.

A 0.2 second measuring period can resolve 5 Hz and therefore .001 uH or .01
pF.

Besides being simple, this oscillator circuit is very reliable in that it
always starts and can tolerate a large variation in the inductance and
capacitance used in the tank circuit.

+ + + + + + + + + + + + + + + + + + + + + +

RF Jim


{Original Message removed}

2002\10\28@042930 by Michael Rigby-Jones

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> -----Original Message-----
> From: Roman Black [SMTP:@spam@fastvidKILLspamspamEZY.NET.AU]
> Sent: Sunday, October 27, 2002 9:08 AM
> To:   KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU
> Subject:      Re: [EE]: Winding inductor for 2 trans. LED blinker
>
> Hi, how does it go with very small inductors and
> zero inductance?? Does it read zero uH if you short
> the terminals with a straight wire,
>
Well, if it has good enough accuracy and resolution it should not read zero
with a straight piece of wire!

Regards

Mike

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