Searching \ for 'Zero crossing dection circuit.' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=zero+crossing+dection
Search entire site for: 'Zero crossing dection circuit.'.

Truncated match.
PICList Thread
'Zero crossing dection circuit.'
1998\06\25@144823 by Bruce Turrentine

picon face
I am working on an automotive timing circuit that uses a toyota reluctor pick
up. It's output is a pseudo sine wave that changes in frequency and amplitude
as the rpm changes. The ideal point to in the wave to send a position
interrupt is as the wave passes zero. I've tried running it through an op amp,
letting the wave swing from a 5v pedestal, and computing the midpoint between
the two peaks but this eats up too much time is an "after the event has come
and gone" solution. Anybody have a suggestion?

Bruce

1998\06\25@155757 by David VanHorn

flavicon
face
>I am working on an automotive timing circuit that uses a toyota reluctor
pick
>up. It's output is a pseudo sine wave that changes in frequency and
amplitude
>as the rpm changes. The ideal point to in the wave to send a position
>interrupt is as the wave passes zero. I've tried running it through an op
amp,
>letting the wave swing from a 5v pedestal, and computing the midpoint
between
>the two peaks but this eats up too much time is an "after the event has
come
>and gone" solution. Anybody have a suggestion?
>
>Bruce


Don't amplify it as a voltage.  Use a current to voltage converter.
That's even a simpler circuit..   Magnets moving past coils create
current. (evidenced by the messnier effect, since a superconductor
has no resistance, there can be no induced voltage!)

This also as the effect of minimizing the effect of the pickup
inductance since it's working into a short. It ruins the Q, making
the transducer much more wideband, and removes almost all
of the self-resonance problems.

We made this mistake with magnetic heads for credit cards too.
The voltage mode circuit is hideous, and has to be tweaked to
a range of frequencies.

1998\06\25@163731 by Timothy D. Gray

flavicon
face
have the op amp clip the wave so all you get are peaks, and just have an
inverter convert the waveform to a ttl square wave. count the frequency
from there.


On Thu, 25 Jun 1998, Bruce Turrentine wrote:

{Quote hidden}

1998\06\25@171145 by Brian Whittaker

flavicon
face
Hi
over Amplify the sine wave and run it through a comparitor
Something like this. Experiment with the circuit values to find the best for
your application. The adjustment vr1 allows you to set the point that the
circuit changes state, from slightly before to slightly after true 0


                        r2                      r5
                   .--\/\/\/\--.-------------\/\/\/\--.
                   |           |                      |
            r1     |    |\     |                      |
Sine in  -\/\/\/\--^----| \    |    r4      |\        |
                        |  >---^--\/\/\/\---| \       |
        Gnd -\/\/\/\----| /                 |  >------+---- output
               r3       |/      .-\/\/\/\---| /       |
                                |    r6     |/        |
                                |        r7           |
                                +---\/\/\/\-----------'
                                |
                     r8         V          r9
          +vcc ---\/\/\/\----\/\/\/\----\/\/\/\--- -vcc
                               vr1

r1 =   1k  r2/r1 sets the gain in this case 100 adjust as necessary
r2 = 100k
r3 =   1k  1/(1/r1+1/r2)=990 ohm 1k is close enough
r4 =  10k  r5/r4 sets the gain in this case 10 adjust as necessary
r5 = 100k
r6 =  10k  1/(1/r4+1/r5)=9090 ohm 10k is close enough
r7 =   5m  (5000k)
r8 =   4k  sets trigger range adjust as necessary
r9 =   4k  sets trigger range adjust as necessary
vr1=  4.7k allows you to adjust the trigger point ahead or behind true dead
center
op1=  any op amp, the lm324 comes to mind it is a quad package
NOTES:

If the input sine wave is large enough the first op amp, r1, r2 and r3 may
not be needed

r7 this resistor adds positive feed back to so that a noisy signal does not
create multiple triggers. Experiment to find the best value. More noise
needs a lower resistor

r3 and r6 are used to null op amp offset. If absolute precision is not
needed replace these resistors with a wire


> {Original Message removed}

1998\06\25@191836 by Sean Breheny

face picon face
On Thu, 25 Jun 1998, David VanHorn wrote:

{Quote hidden}

This is not quite true, AFAIK. Faraday's law says EMF = k * d phi / dt

where k is a constant depending on what system of units you are using and
phi is the magnetic flux thru the coil. Notice that current is not
mentioned here.

Current comes into the picture as resistance approaches zero. In this
case, it is easier to use Lenz's law which states that with zero
resistance, the amount of current flowing in a coil will be such that the
field due to the coil will cancel out can flux changes due to itself or
the external environment.

So, unless I am wrong (I could be, but I just took physics E&M last
semester), even in something which has near zero resistance, the voltage
induced in the entire loop will be as given by Faraday's law. A
superconductor is a special case and standard analysis techniques usually
applied to wire won't work very well. It represents a mathmatical
singularity (because is creates a division by zero in several of the
formulas involved).

>
> This also as the effect of minimizing the effect of the pickup
> inductance since it's working into a short. It ruins the Q, making
> the transducer much more wideband, and removes almost all
> of the self-resonance problems.
>

I think that this is the REAL reason why the current to voltage converter
works best, because the loop sees a short. The easiest law to apply to
this case will be Lenz's, implying that the loop is inherently a current
producer, however, I think that if you measured the total resistance of
the circuit and multiplied by the current, the voltage you would see
would be that given by Faraday's law.

> We made this mistake with magnetic heads for
credit cards
too.
> The voltage mode circuit is hideous, and has to be tweaked to
> a range of frequencies.
>

I know that what I am saying is REALLY splitting hairs, but I just want
to see how well what I have learned applies to real life situations :)

Sean

1998\06\25@194209 by TONY NIXON 54964

flavicon
picon face
Use hardware based on the MC3334 ignition chip from Motorola. It's
cheap and will give you a nice square wave from the reluctor to the PIC. The
interface to my programmable ignition system uses it.

Regards

Tony


PicNPoke Multimedia 16F84 Beginners PIC Tools.

**PLUS** - PicNPlay - PicNPlan - PicNPrep - PicNPost
PicNPort - DT Type Saver - *new* PicNQuiz.
Recent addition - Hex To Source converter.

http://www.picnpoke.com
Email spam_OUTpicnpokeTakeThisOuTspamcdi.com.au

1998\06\25@195301 by David VanHorn

flavicon
face
>> This also as the effect of minimizing the effect of the pickup
>> inductance since it's working into a short. It ruins the Q, making
>> the transducer much more wideband, and removes almost all
>> of the self-resonance problems.
>>
>I think that this is the REAL reason why the current to voltage converter
>works best, because the loop sees a short. The easiest law to apply to
>this case will be Lenz's, implying that the loop is inherently a current
>producer, however, I think that if you measured the total resistance of
>the circuit and multiplied by the current, the voltage you would see
>would be that given by Faraday's law.


I agree with what you said, but IMHO, the basic phenomena is that
charged particles traversing a magnetic field are deflected. You can't
define a voltage until there is a resistance.  That's where Faraday
and Lenz take opposite paths (or join, depending on your point of
view :)

The real coil will have some R, and so will retain some L, and will
still have a self resonant point, but the effect of this on the circuit's
performance in the real world will be very small.

I came into this from the opposite direction as well, having tons
of experience with magnetic read heads and credit cards, and
amplifying the head as a voltage. It's really rather miserable.
Once I figured out this approach, things got a WHOLE lot simpler.
We no longer need sheilded cables either!

>I know that what I am saying is REALLY splitting hairs, but I just want
>to see how well what I have learned applies to real life situations :)


Good deal!  Rabbit blood everywhere :)
The fun part is when the real circuit departs from the theoretical in ways
that are difficult to measure!

1998\06\26@161415 by Scott Newell

flavicon
face
>We made this mistake with magnetic heads for credit cards too.
>The voltage mode circuit is hideous, and has to be tweaked to
>a range of frequencies.

I've thought of using a current mode circuit for audio tapes--at least
until I read a Winfield Hill post on the 'net.  He was building a digital
tape drive (probably the same one in the AoE), and they tried using the
current from the head.

The only problem was the shorted turn they created from the tape reader
head slowly erased the tapes, high frequencies first!

Did you have any similiar problems?


later,
newell

ps.
Found the post of DejaNews, in case you're interested:
{Quote hidden}

1998\06\26@205529 by David VanHorn

flavicon
face
>>We made this mistake with magnetic heads for credit cards too.
>>The voltage mode circuit is hideous, and has to be tweaked to
>>a range of frequencies.
>
>I've thought of using a current mode circuit for audio tapes--at least
>until I read a Winfield Hill post on the 'net.  He was building a digital
>tape drive (probably the same one in the AoE), and they tried using the
>current from the head.
>
>The only problem was the shorted turn they created from the tape reader
>head slowly erased the tapes, high frequencies first!
>


This seems fantastic.   (Although I give the source considerable weight!)

AFAIK, it is impossible.  Even if the shorted turn were a superconductor,
the resultant field strength could only approach the field strength on the
card, and this is not enough to erase it.

I've not seen any evidence of this, even in trials where we ran cards
through
the reader 10,000 times. They are only mechanically rated for about 2000
passes, and they begin to fall apart. We didn't see any degradation.
At that point, we're examining signal waveforms, looking for indications
that the head is wearing, and at the magstripe itself, for abnormal wear
patterns that would indicate the head being asymmetrically loaded against
the card.  Still, we would have seen it in the waveforms.

It might be an artifact of the media, but even so, this goes against
everything
I've ever read on the subject.  (tab books has an excellent book by Finn
Jorgensen)

There is a phenomena where some domains saturate at a lower field strength
than others, this is very dependent on the media.

I even went over this technique at length with the engineers at Vikron, and
they
saw no problems with it.

I wonder if something else was happening in Win's case?


{Quote hidden}

1998\06\30@182819 by Sean Breheny

face picon face
On Fri, 26 Jun 1998, David VanHorn wrote:

> >The only problem was the shorted turn they created from the tape reader
> >head slowly erased the tapes, high frequencies first!
> >
>
>
> This seems fantastic.   (Although I give the source considerable weight!)
>
> AFAIK, it is impossible.  Even if the shorted turn were a superconductor,
> the resultant field strength could only approach the field strength on the
> card, and this is not enough to erase it.

Obviously, you have MUCH more experience than I do with magnetic media,
however, if I remember my theory correctly, with ferromagnetic materials,
much less field is required to magnetize (or reverse the polarity) of a
piece of material than the total filed of that piece. In otherwords, if
you look at the B-H curve, the H is MUCH less than B, so, for example, if
for H=0, B=100 Gauss, you might only need to bring H down to maybe 10
Gauss in the opposite direction to make B=0, or bringing H down to 20 in
the opposite direction might make B=100 Gauss in that new, opposite
direction. So, the if the field created by the current induced in the
pickup loop were greater than 1/mu times the original B of the material,
then if seems to me that it could demagnetize it.

Again, there probably is something I am not seeing :)

Sean


{Quote hidden}

More... (looser matching)
- Last day of these posts
- In 1998 , 1999 only
- Today
- New search...