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PICList Thread
'pic tachometer...'
1998\01\12@161331 by Jeff Cesnik

flavicon
face
Once again I'm drawing upon the infinite wisdom of the PICLIST...

 I'm building a simple pic-based automotive tachometer and would like
to count pulses from the primary lead of the ignition coil and display
the RPM on an LCD.  For peace-of-mind (and other reasons), I'd like to
isolate the input pin of the pic with a 4N35 optoisolator.  I can handle
everything but the connection to the coil...

I have 2 questions -

1.  What is the maximum frequency that the 4N35 will reliably switch at
(will it keep up with the pulse train from the coil)?

2.  What do I need to do at the optoisolator's input to handle the
ignition pulses?


-Thanks

1998\01\12@175309 by TONY NIXON 54964

flavicon
picon face
If you can understand my description, this circuit works fine.

                     +12V                                   +5V
                        |      k                                    |
                 IN4004                                     4K7
                        |      a                                     |
                   100R                                         *----out
Points               |                                             |
--------10K-----*-------*---10K----*------BC338
                        |          |                  |                |
                   100R     10n            10K            |
                k     |           |                  |            Gnd
                 IN4004     |              Gnd
                a     |         Gnd
                   Gnd



Tony

For the beginner....
PicNPoke Multimedia 16F84 Simulator Assembler, and Tutorial.
Now with PicNPlay circuit simulator.
Plus animated Address Mode Tutor.

http://www.dontronics.com/picnpoke.html

1998\01\13@025951 by STEENKAMP [M.ING E&E]

flavicon
picon face
Hi,

> Once again I'm drawing upon the infinite wisdom of the PICLIST...
>
>   I'm building a simple pic-based automotive tachometer and would like
> to count pulses from the primary lead of the ignition coil and display
> the RPM on an LCD.  For peace-of-mind (and other reasons), I'd like to
> isolate the input pin of the pic with a 4N35 optoisolator.  I can handle
> everything but the connection to the coil...
>
> I have 2 questions -
>
> 1.  What is the maximum frequency that the 4N35 will reliably switch at
> (will it keep up with the pulse train from the coil)?
>
> 2.  What do I need to do at the optoisolator's input to handle the
> ignition pulses?
>
Just a comment:
I have also constructed an automotive tachometer about a year ago.  I
have found that counting pulses in a fixed period is not a very good
approach, since the frequency of pulses can be quite low.  At 600 RPM it
is 20Hz for a 4cyl engine.  That means that your counting period must be
quite long to be able to get sufficient accuracy, which means a
slow update rate of the display.  The method I used was to time the
period between two pulses and calculate the RPM from that.  I
wanted to keep the refresh rate between 5 and 10 times per second.  Since
the higher the RPM's the shorter the period, I was also able to average
samples at higher RPM's for a stabler display.  From 0 to 1200RPM's I
used 1 sample, from 1200 to 2400 I used 2 samples.  From 2400 to 4800 I
used 4 samples and from 4800 upwards I used 8 samples.

The project uses a 16C54 running at 20MHz and the display is a 16x2 LCD.
It has a resolution of 10RPM's.  In the top line of the LCD I display the
RPM's in digits and in the bottom line I have a bargraph display (made by
using the programmable characters of the LCD).  The display is
really fast and responsive.
I guess that using one of the PIC's with a capture and compare unit
would have been easier, but I wanted to see what I could do with a 54!

Regards,
Niki

1998\01\13@100420 by Keith Howell

flavicon
face
A friend of mine once built an Acorn Atom add-on that allowed him to
measure resistance or capacitance by timing the frequency or period of an
RC oscillator. For high frequencies, it's more accurate to count cycles.
At low frequencies, it's better to time the period.

At some frequency between, the two methods are equally accurate.
He worked out this crossover point, and thus the accuracy was always
guaranteed better than a minimum figure.

You may wish to use this method for your project.

1998\01\13@115530 by John Payson

picon face
> A friend of mine once built an Acorn Atom add-on that allowed him to
> measure resistance or capacitance by timing the frequency or period of an
> RC oscillator. For high frequencies, it's more accurate to count cycles.
> At low frequencies, it's better to time the period.
>
> At some frequency between, the two methods are equally accurate.
> He worked out this crossover point, and thus the accuracy was always
> guaranteed better than a minimum figure.

An alternative which will always give maximal accuracy, but which requires
a little more calculation effort, is to time as many pulses as will fit in
a second; then take the time from the first to the last and divide that
into the number of event intervals received.  If the signal is, e.g.,
100.7Hz you may receive 101 pulses, with 993,050us between the first and
the last.  Dividing 0.993050 into 100 event intervals yields 100.700Hz (if
the time is accurate to within 10us).  This approach is often far more acc-
urate than pulse-counting or period-measurement alone.

1998\01\13@134345 by Montaigne, Mike

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face
I think you project is neat!
Would you be willing to share your code (just for personal
non-commercial use).
tks

Mike Montaigne
spam_OUTmontaignemTakeThisOuTspamaecl.ca

{Quote hidden}

1998\01\13@134357 by Roger L Stevens

picon face
John Payson wrote :

>An alternative which will always give maximal accuracy, but which
requires
>a little more calculation effort, is to time as many pulses as will fit
in
>a second; then take the time from the first to the last and divide that
>into the number of event intervals received.  If the signal is, e.g.,
>100.7Hz you may receive 101 pulses, with 993,050us between the first and
>the last.  Dividing 0.993050 into 100 event intervals yields 100.700Hz
(if
>the time is accurate to within 10us).  This approach is often far more
acc-
>urate than pulse-counting or period-measurement alone.

NOTE: When using this scheme:

The beginning of the 1 second period (window) should be synchronous with
(begin at the same time as) the event (pulse) and only the subsequent
events are to be counted in the 1 second period.

If the 1 second window begins more than one-half event period after the
event, then one too many events will fit into the 1 second window.

SO: the 1 second window must start less than one-half event period after
the event. The easiest way to ensure this is to start the window at the
event.

Roger
********************************
Certified Jowett Nut
(If you have to ask..you are better off not knowing about Jowetts)

1998\01\13@163337 by Wim E. van Bemmel

picon face
Jeff Cesnik wrote:

> Once again I'm drawing upon the infinite wisdom of the PICLIST...
>
>   I'm building a simple pic-based automotive tachometer and would like
> to count pulses from the primary lead of the ignition coil and display
> the RPM on an LCD.  For peace-of-mind (and other reasons), I'd like to
> isolate the input pin of the pic with a 4N35 optoisolator.  I can handle
> everything but the connection to the coil...
>
> I have 2 questions -
>
> 1.  What is the maximum frequency that the 4N35 will reliably switch at
> (will it keep up with the pulse train from the coil)?
>
> 2.  What do I need to do at the optoisolator's input to handle the
> ignition pulses?
>
> -Thanks

Hello,

I intend to build such a device too,
for my small yacht, that has a Sabb 8 hp Diesel engine.. no ignition by
electric means, and mechanical fuel injection.
Has anyone EXPERIENCE  with getting RPM info out of a diesel engine? Please no
untested ideas, I have plenty myself, just proven technology! Accuracy is not
the primary goal.
One of my better ideas is using the jerk of the fuel injection pipe.. anyone
tried that?
Must be verry reliable, and sea water resistant, in a dirty environment...
The engine has a flywheel with a diameter of about 50 cm (20"), that is
difficult to access from the front. The clutch is in the engine block, so the
outgoing shaft may be disconnected, so using that is not absolutely reliable.
The engine drives an AC generator through a V-belt. The start motor is a Bosch
Dynastart, attached by V-belt also.
No more V-belts can be driven.
Getting the RPM info is in my opinion the hardest part, interfacing it to the
PIC is a challenge, the rest is FUN though a challenge to me, as a novice in
PIC world!

1998\01\13@193631 by TONY NIXON 54964

flavicon
picon face
I imagine that the engine RPM is fairly low (2000 - 3000 RPM), so why
not attatch a small steel vane (or more) on the pulley on the crank
shaft (or even the alternator pulley) and use an integrated Hall Effect/Magnet
assembly to sense when the vane passes through it. Use the PIC to decode
and display the RPM. These things work up to 130C so temp shouldn't
be a problem. The units are fully sealed and it shouldn't matter if the vane(s)
pick up a bit of sump residue, as long as it is not metallic (unlikely).

Some of these engines have a tacho drive which comes off the injector
pump. Maybe you could use this to drive a similar sensor setup and as
it is cable driven it would be remote from the engine compartment. I
made a digital speedo which sensed the rotation of the magnet
assembley inside an old speedo housing and it worked quite well.


Regards

Tony

For the beginner....
PicNPoke Multimedia 16F84 Simulator Assembler, and Tutorial.
Now with PicNPlay circuit simulator.
Plus animated Address Mode Tutor.

http://www.dontronics.com/picnpoke.html

1998\01\13@200205 by peter

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face
Wim E. van Bemmel wrote:

>  Hello,
>
> I intend to build such a device too,
> for my small yacht, that has a Sabb 8 hp Diesel engine.. no ignition by
> electric means, and mechanical fuel injection.

snip

> The engine drives an AC generator through a V-belt. The start motor is a Bosch
> Dynastart, attached by V-belt also.
> No more V-belts can be driven.
> Getting the RPM info is in my opinion the hardest part, interfacing it to the
> PIC is a challenge, the rest is FUN though a challenge to me, as a novice in
> PIC world!

On some Mercedes trucks the first sign of alternator brush failure is
erratic rpm readings

I've never had cause to delve deeper into this but this must be that
the RPM is measured via the Alternator

I never really looked hard at the system wiring but I believe they
only use two wires ie. 12v and ground

The ripple is probably large enough to measure easily
though frequency to rpm will not be a simple
divide by two/three/four etc, as for petrol engines

Alternators have twelve? poles three phases
12? x3= 36 pulses per alternator rev
reduction  2:1 ? =18 pulses per engine rev

700 to 4000 rpm = 210Hz to 1200Hz
easy to filter and time/count
any extra pulses from switches
will have little effect on the reading

--
If God so loved the World (and created it)
then why is it so imperfect
It's got more bugs than windoze 95

.....peterKILLspamspam.....cousens.her.forthnet.gr

1998\01\13@210749 by richard skinner

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face
We had a pulse indicator that went inline with the injector line,  but
I had a friend, who claims he installed a pickup on the valve cover
pointing down towards a rocker arm.  Each time the rocker arm went down
it would send a pulse.  He would then multiply and divide to get rpm.
He had the same problem finding a place to access a rotating shaft, and his
valve cover was cast alum.  which made it easy to dill and tap.

This is a wild way, but it does provide a solution.


Richard Skinner
EraseMErwskinnerspam_OUTspamTakeThisOuTworldnet.att.net

>  Hello,
>
> I intend to build such a device too,
> for my small yacht, that has a Sabb 8 hp Diesel engine.. no ignition by
> electric means, and mechanical fuel injection.
> Has anyone EXPERIENCE  with getting RPM info out of a diesel engine? Please
no
> untested ideas, I have plenty myself, just proven technology! Accuracy is
not
> the primary goal.
> One of my better ideas is using the jerk of the fuel injection pipe..
anyone
> tried that?

> Must be verry reliable, and sea water resistant, in a dirty environment...
> The engine has a flywheel with a diameter of about 50 cm (20"), that is
> difficult to access from the front. The clutch is in the engine block, so
the
> outgoing shaft may be disconnected, so using that is not absolutely
reliable.
> The engine drives an AC generator through a V-belt. The start motor is a
Bosch
> Dynastart, attached by V-belt also.
> No more V-belts can be driven.
> Getting the RPM info is in my opinion the hardest part, interfacing it to
the
> PIC is a challenge, the rest is FUN though a challenge to me, as a novice
in
> PIC world!

1998\01\13@233830 by tjaart

flavicon
face
> > A friend of mine once built an Acorn Atom add-on that allowed him to
> > measure resistance or capacitance by timing the frequency or period of an
> > RC oscillator. For high frequencies, it's more accurate to count cycles.
> > At low frequencies, it's better to time the period.
> >
> > At some frequency between, the two methods are equally accurate.
> > He worked out this crossover point, and thus the accuracy was always
> > guaranteed better than a minimum figure.

You have to ask yourself if you want more accuracy than what you are
going
to display. By choosing your timebase properly, you only have to count
the
pulses between display updates. 50RPM, or 50.00001RPM - your car engine
is
going to stall either way!

--
Friendly Regards

Tjaart van der Walt
tjaartspamspam_OUTwasp.co.za
_____________________________________________________________
| WASP International http://www.wasp.co.za/~tjaart/index.html |
|       R&D Engineer : GSM peripheral services development    |
|   Vehicle tracking | Telemetry systems | GSM data transfer  |
|    Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973    |
|              WGS-84 : 26¡10.52'S 28¡06.19'E                 |
|_____________________________________________________________|

1998\01\14@015614 by Pasi T Mustalahti

picon face
On Tue, 13 Jan 1998, John Payson wrote:

> An alternative which will always give maximal accuracy, but which requires
> a little more calculation effort, is to time as many pulses as will fit in
> a second; then take the time from the first to the last and divide that
> into the number of event intervals received.  If the signal is, e.g.,
> 100.7Hz you may receive 101 pulses, with 993,050us between the first and
> the last.  Dividing 0.993050 into 100 event intervals yields 100.700Hz (if
> the time is accurate to within 10us).  This approach is often far more acc-
> urate than pulse-counting or period-measurement alone.

PTM: How does this differ from pulse-counting ? The original problem is
still there, however you describe the method: at low frequencies you have
only so many pulses. The maximum accuracy will be D=0.5/f/T
(T=measurement time). When the measurement time is one second: 0.05% @
1000Hz, 0.5% @ 100Hz, 5% @ 10Hz, 50% @ 1 Hz ... (If I made it right after
3 h sleep:).
The error comes in, because the last pulse in the measurement time will
allways be in a different phase than the first. You got to measure the
phase difference to make the accuracy better. There you got to use the
period-measurement at last for the last pulse. To do that, you've got to
have a system which see to the length of the last pulse in advance. OR
measure continuously with both methods.
If you want to have the same accuracy all the time, you have to measure
the same amount of pulses every time. For example 500 to have an accuracy
of 1%. This is even worse, because the frequency can change between the
start and stop moments. To compensate this you have to make parallel
measurements and indicate somehow that there has been some kind of a
change.
Measuring a frequency with accuracy of 1% makes allways the last number to
be '8' if you have a display with 4 digits and the frequency is >1000Hz.

--------------------------------------------------------------------------
PTM, @spam@pasi.mustalahtiKILLspamspamutu.fi, KILLspamptmustaKILLspamspamutu.fi, http://www.utu.fi/~ptmusta
Lab.ins. (mikrotuki) ATK-keskus/Mat.Luon.Tdk                    OH1HEK
Lab.engineer (PC support) Computer Center                       OI7234
Mail: Turun Yliopisto / Fysla, Vesilinnantie 5, 20014
Pt 02-3336669, FAX 02-3335632 (Pk 02-2387010, NMT 049-555577)
--------------------------------------------------------------------------

1998\01\14@020654 by Pasi T Mustalahti

picon face
On Tue, 13 Jan 1998, Wim E. van Bemmel wrote:

> Jeff Cesnik wrote:
>
> > Once again I'm drawing upon the infinite wisdom of the PICLIST...
>
> I intend to build such a device too,
> for my small yacht, that has a Sabb 8 hp Diesel engine.. no ignition by
> electric means, and mechanical fuel injection.
> Has anyone EXPERIENCE  with getting RPM info out of a diesel engine?
PTM: I bored and clued a small magnet to the flywheel and read it with a
self made coil. There was a 4xOP-AMP to get the pulse out for a normal
cheap tachometer from a car. The same tacho was used to measure the water
lewel in the water tank so there was a switch. The face of the tachometer
I made myself, because the frequency from the flywheel is twice too high.
My friend took the pulse out from AC generator.
--------------------------------------------------------------------------
PTM, RemoveMEpasi.mustalahtiTakeThisOuTspamutu.fi, spamBeGoneptmustaspamBeGonespamutu.fi, http://www.utu.fi/~ptmusta
Lab.ins. (mikrotuki) ATK-keskus/Mat.Luon.Tdk                    OH1HEK
Lab.engineer (PC support) Computer Center                       OI7234
Mail: Turun Yliopisto / Fysla, Vesilinnantie 5, 20014
Pt 02-3336669, FAX 02-3335632 (Pk 02-2387010, NMT 049-555577)
--------------------------------------------------------------------------

1998\01\14@031134 by John Payson

picon face
> > An alternative which will always give maximal accuracy, but which requires
> > a little more calculation effort, is to time as many pulses as will fit in
> > a second; then take the time from the first to the last and divide that
> > into the number of event intervals received.  If the signal is, e.g.,
> > 100.7Hz you may receive 101 pulses, with 993,050us between the first and
> > the last.  Dividing 0.993050 into 100 event intervals yields 100.700Hz (if
> > the time is accurate to within 10us).  This approach is often far more acc-
> > urate than pulse-counting or period-measurement alone.
>
> PTM: How does this differ from pulse-counting ? The original problem is
> still there, however you describe the method: at low frequencies you have
> only so many pulses.
...
> The error comes in, because the last pulse in the measurement time will
> allways be in a different phase than the first. You got to measure the
> phase difference to make the accuracy better. There you got to use the
> period-measurement at last for the last pulse. To do that, you've got to
> have a system which see to the length of the last pulse in advance. OR
> measure continuously with both methods.

If you know the time between a particular pulse, and a later pulse, you'll
know the frequency as accurately as you know the time (i.e. if you know
the time to 5 sig figs, you'll know the frequency to about 5 sig figs).

> If you want to have the same accuracy all the time, you have to measure
> the same amount of pulses every time. For example 500 to have an accuracy
> of 1%. This is even worse, because the frequency can change between the
> start and stop moments. To compensate this you have to make parallel
> measurements and indicate somehow that there has been some kind of a
> change.

If the frequency is changing quickly relative to your measurement interval,
then you obviously have a problem.  If it isn't, however, why does it matter
whether you always use the same number of pulses when you time the period,
rather than using 493 sometimes, 23 other times?  You know, after all, prec-
isely how many pulses you DO have...

> Measuring a frequency with accuracy of 1% makes allways the last number to
> be '8' if you have a display with 4 digits and the frequency is >1000Hz.

Huh?

1998\01\14@042726 by STEENKAMP [M.ING E&E]

flavicon
picon face
Hi,

If anyone would like to see the code and the schematic, mail me and I'll
mail it to you.

Regards,
Niki

{Quote hidden}

1998\01\14@045016 by Anders Eliasson

flavicon
face
Hi,


Your design seems very neat, I'd be very thankful if you send me the
code/schematics.

Thanks

Best Regards
Anders Eliasson



At 11:26 1998-01-14 GMT+0200, you wrote:
{Quote hidden}

1998\01\14@045434 by STEENKAMP [M.ING E&E]

flavicon
picon face
> > A friend of mine once built an Acorn Atom add-on that allowed him to
> > measure resistance or capacitance by timing the frequency or period of an
> > RC oscillator. For high frequencies, it's more accurate to count cycles.
> > At low frequencies, it's better to time the period.
> >
> > At some frequency between, the two methods are equally accurate.
> > He worked out this crossover point, and thus the accuracy was always
> > guaranteed better than a minimum figure.
>
> An alternative which will always give maximal accuracy, but which requires
> a little more calculation effort, is to time as many pulses as will fit in
> a second; then take the time from the first to the last and divide that
> into the number of event intervals received.  If the signal is, e.g.,
> 100.7Hz you may receive 101 pulses, with 993,050us between the first and
> the last.  Dividing 0.993050 into 100 event intervals yields 100.700Hz (if
> the time is accurate to within 10us).  This approach is often far more acc-
> urate than pulse-counting or period-measurement alone.

This is in effect the same as period-measurement - you just spread your
measuring error over multiple periods.  For an automotive tachometer,
though, the prime concern is responsiveness.  The display must reflect
the current RPM's as closely as possible.  You could segment your span
into a different sections.  At low RPM's you measure one period time, at
slightly higher RPM's you you measure 2 period times and so on.  This is
very useful also to keep your update time relatively constant as well.
Another thing to keep in mind is the size of your period counter.  To get
the highest possible timing resolution, you need to increment your
period timer as fast as possible.  That means that the more periods you
time, the larger your counter must be and the more complex the division
needed to convert period to frequency.  This might be a problem,
depending on the PIC you use.

Regards
Niki

1998\01\14@073129 by in Harris & Alison Smith

picon face
>
> Hello,
>
>I intend to build such a device too,
>for my small yacht, that has a Sabb 8 hp Diesel engine.. no ignition by
>electric means, and mechanical fuel injection.
>Has anyone EXPERIENCE  with getting RPM info out of a diesel engine?
Please no
>untested ideas, I have plenty myself, just proven technology! Accuracy is not
>the primary goal.
>One of my better ideas is using the jerk of the fuel injection pipe.. anyone
>tried that?
>Must be verry reliable, and sea water resistant, in a dirty environment...
>The engine has a flywheel with a diameter of about 50 cm (20"), that is
>difficult to access from the front. The clutch is in the engine block, so the
>outgoing shaft may be disconnected, so using that is not absolutely reliable.
>The engine drives an AC generator through a V-belt. The start motor is a
Bosch
>Dynastart, attached by V-belt also.
>No more V-belts can be driven.
>Getting the RPM info is in my opinion the hardest part, interfacing it to the
>PIC is a challenge, the rest is FUN though a challenge to me, as a novice in
>PIC world!
>

One way of getting a signal is to pick up from the Alternator windings
directly. This should give you a nice sine wave to shape up.
I have seen a truck Alternator with a take off terminal for this purpose
Hope this helps

All the best,
Kevin

1998\01\14@075921 by Martin McCormick

flavicon
face
"Wim E. van Bemmel" writes:
>The engine drives an AC generator through a V-belt.

       That would seem to be the best hope if I was doing this project.
Someone has already done the mechanics for you so all you need to do is
what somebody else already suggested and read the ripple frequency.  It should
give a very high resolution since the alternator is usually spun at several
times the engine speed in order to allow charging at idle.  I can't imagine
that the system is so free of ripple that a few millivolts can't be
capacitively coupled in to an amplifier to be digitally sampled.

       You asked for no untested ideas and I can state categorically that
alternator ripple is one of the biggest headaches in mobile communications
electronics.  You actually should have about two volts (on a 12-volt system)
of alternator signal when the engine is running so your tachometer just
needs a power lead from the electrical system and you should be ready for
speed measurements.  The only thing that is peculiar to the setup is to
establish a relationship between engine RPM and alternator output frequency
and that is a one-time linear constant.

       One cautionary thought comes to mind.  This might seem like the
basis for an automated throttle control system and it could be except that one
would definitely need to have some sort of fail safe system to guard against
the run-away condition that would result from a broken or badly slipping
alternator belt or failed alternator, itself.

Martin McCormick

1998\01\14@085917 by Pasi Mustalahti

picon face
>If anyone would like to see the code and the schematic, mail me and I'll
>mail it to you.
>
>Regards,
>Niki
>
>> I think you project is neat!
>> Would you be willing to share your code (just for personal
>> non-commercial use).
>> tks
>>
PTM: Me too !!!

1998\01\14@152634 by Stein Sem-Jacobsen

picon face
>Hi,
>
>If anyone would like to see the code and the schematic, mail me and I'll
>mail it to you.
>
>Regards,
>Niki


I'd really appreciate it.


Stein Sem-Jacobsen

1998\01\14@163911 by PHXSYS

picon face
Please send sample code

Thank you

Jon

1998\01\15@013343 by Kevin Howell

flavicon
face
Wim E. van Bemmel wrote:

{Quote hidden}

  You can get a perfect square wave from the alternator of the engine.
Solder a wire onto any of the diodes on the rectifier plates. This will
give you a perfect square wave output of the same voltage as is the
battery!

If you don't understand or need more info please mail me personnally...

Kevin Howell

1998\01\15@020723 by Nigel Goodwin

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In message <RemoveME34BBD0C0.573DAAA0TakeThisOuTspamspamxs4all.nl>, "Wim E. van Bemmel"
<EraseMEbemspanspamspamspamBeGoneXS4ALL.NL> writes
>I intend to build such a device too,
>for my small yacht, that has a Sabb 8 hp Diesel engine.. no ignition by
>electric means, and mechanical fuel injection.
>Has anyone EXPERIENCE  with getting RPM info out of a diesel engine? Please no
>untested ideas, I have plenty myself, just proven technology! Accuracy is not
>the primary goal.
>One of my better ideas is using the jerk of the fuel injection pipe.. anyone
>tried that?
>Must be verry reliable, and sea water resistant, in a dirty environment...
>The engine has a flywheel with a diameter of about 50 cm (20"), that is
>difficult to access from the front. The clutch is in the engine block, so the
>outgoing shaft may be disconnected, so using that is not absolutely reliable.
>The engine drives an AC generator through a V-belt. The start motor is a Bosch
>Dynastart, attached by V-belt also.
>No more V-belts can be driven.
>Getting the RPM info is in my opinion the hardest part, interfacing it to the
>PIC is a challenge, the rest is FUN though a challenge to me, as a novice in
>PIC world!

Is the engine cooled by a mechanical fan, a common technique for diesel
engines is to read the roration speed of the fan optically - just like a
tachometer for a model airplane engine.
--

Nigel.

       /--------------------------------------------------------------\
       | Nigel Goodwin   | Internet : RemoveMEnigelgKILLspamspamlpilsley.demon.co.uk     |
       | Lower Pilsley   | Web Page : http://www.lpilsley.demon.co.uk |
       | Chesterfield    |                                            |
       | England         |                                            |
       \--------------------------------------------------------------/

1998\01\15@063404 by Pasi T Mustalahti

picon face
On Wed, 14 Jan 1998, John Payson wrote:
> > Measuring a frequency with accuracy of 1% makes allways the last number to
> > be '8' if you have a display with 4 digits and the frequency is >1000Hz.
>
> Huh?
PTM: If you have to easure something that has a rippel of say 1%, your
meter vill show you 2 sharp digits. The third changes from 0 to 9 all the
time. If this fluctuation is fast enoug, you see a dim '8'.
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1998\01\15@185722 by Graham, Peter

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part 0 1754 bytes

{Quote hidden}

       If you have access to the front of the crank shaft, try mounting
a disk with a notch cut out on to it and use a hall effect sensor. You
will get a 5V pulse which is easy to count with the PIC's. It works for
auto engine control so it should work here.

       If you have any questions email me.

       Peter G.
       KILLspampeter.grahamspamBeGonespamdsto.defence.gov.au

1998\01\15@190559 by Dean

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part 0 2913 bytes content-type:application/octet-stream; name="tach.gif"Dean.

(-;     Ever stop to think...................... and forget to start again?

;-)

[Tach.txt]
AUTOMOTIVE TACHOMETER (the schematic is named tach.gif)

Circuit for an automobile tachometer using the LM2907 or LM2917 frequency
to
voltage converters. The  LM2917 has a regulator onboard. The circuit is the
same
for 4,6 or 8 cylinder engines. However, the  component values are
different. On a
gasoline powered engine, the pickup (input) comes from the  distributor.
Most
distributor caps have a tap-off that can be used. The circuit can be
adopted for use
with a  diesel engine. On the diesel engine, tap into the varying A.C.
voltage
coming off the alternator. The  equations used with this chip are:
Vo=Vcc x Fin x R1 x C1: where  Vo=output voltage, Vcc= supply voltage,
Fin=input frequency in hertz,  R1=resistance of R1, C1=capacitance of C1
and RPM=(120 x freq.) / (# of cylinders): to find the input frequency
depending on
the engine RPMs and  the number of cylinders.

DESCRIPTION & CONSTRUCTION
Design of circuit for a four cylinder gasoline engine.
RPM   Freq., Hz   Io(uA)
1000       33.3        17
2000       66.6        33
3000       100         50
4000       133         67
5000       166         83
6000       200         100

Using a 100uA meter movement and the 14 pin LM2917 package, the following
component values are used. For  the LM2917 Vcc=7.5V when the voltage
regulator is used.

Calculate the value of R1 x C1, and pick a common value for the capacitor.
In this
case, .01uF was picked.  This makes the value for R1=360K. The
capacitor(.1uF) in
parallel with R1 is used to damp the meter. This may  have to be changed
depending on the meter movement. The full scale meter deflection(100uA in
this
case)  is set using the 10K pot in series with the 39K resistor connected
to
pin 5. The input frequency is divided  and filtered prior to input to pin
1. These
values may have to be changed dependent on the specific  automobile engine.
All
resistors are half watt. Capacitors are non-polarized disc, mylar or
tantalum. The
diode is 1N4001.

Construct the circuit on a vector board. Ensure the potentiometer is placed
for easy
access. The entire  circuit can be fitted to the input terminals of the
meter. This
makes for a clean, compact tachometer that  can be mounted anywhere.

CALIBRATION
Calibrate the meter before installation using a pulse generator. Set the
generator to
the maximum input  frequency, 1.5 mS pulse width, 10 V amplitude. Adjust
the
10K pot to get 100uA meter reading. Check all  frequencies for the correct
output
current.

Bob Ausman
Questions should be directed via Internet E-mail to:
EraseMEausmanspamEraseMEtecnet1.jcte.jcs.mil

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Content-Description: tach.gif (ACDSee GIF Image)
Content-Disposition: attachment; filename="tach.gif"

Attachment converted: wonderland:tach.gif (GIFf/JVWR) (0000FD0C)

1998\01\16@121552 by DREITEK

picon face
In a message dated 98-01-15 18:58:16 EST, you write:

<< >
        If you have access to the front of the crank shaft, try mounting
a disk with a notch cut out on to it and use a hall effect sensor. You
will get a 5V pulse which is easy to count with the PIC's. It works for
auto engine control so it should work here.

        If you have any questions email me.

        Peter G.
        @spam@peter.graham@spam@spamspam_OUTdsto.defence.gov.au >>

Hello Peter,
A hall effect sensor won't detect a disk with a notch cut out of it.  An
optical interupter sensor will.  Hall effect sensors detect magnetic fields.
You could simply strap a good rare earth magnet to the crank shaft and detect
that with a Hall sensor.  They do that for auto trip computers.  I designed
one about five years ago.  We had a magnet held to the drive shaft by two
cable ties.  Worked OK.

Sorry to be nit picky
Dave Duley

1998\01\16@193747 by Bill (WL) Boulton

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Dave Dudley
At 12:10 PM 16/01/98 EST, you wrote:

>A hall effect sensor won't detect a disk with a notch cut out of it.  An
>optical interupter sensor will.  Hall effect sensors detect magnetic fields.
--------snip-----------

A raw hall sensor won't but try using one of the auto spec devices with the
magnet built in. The not produces a disturbance in the field which .....

Alternatively, you could use a reluctor sensor from an old Volvo or the
rear wheel speed sensor from a BMW K100 motorbike. This only requires a peg
in the flywheel (use 2 to keep balance) to trigger. These units have
inbuilt magnets, respond at low revs (eg, starting) and are super reliable
(can't kill it with dirt or oil). Watch the bi-polar pulse at revs. It bites!

Bill

1998\01\16@203413 by DREITEK

picon face
In a message dated 98-01-16 19:38:18 EST, you write:

<<
A raw hall sensor won't but try using one of the auto spec devices with the
magnet built in. The not produces a disturbance in the field which .....

Alternatively, you could use a reluctor sensor from an old Volvo or the
rear wheel speed sensor from a BMW K100 motorbike. This only requires a peg
in the flywheel (use 2 to keep balance) to trigger. These units have
inbuilt magnets, respond at low revs (eg, starting) and are super reliable
(can't kill it with dirt or oil). Watch the bi-polar pulse at revs. It bites!

Bill
 >>
Bill
Its DULEY  not DUDLEY
All the original post said was Hall effect sensor.  I have used the Interupter
type hall sensors.  They are very expensive!
Around $80 US.  I know because we killed a few because the metallic flag we
were using wasn't aligned right and we kept cutting the sensor in half.  Cool
little cubic rare earth magnets inside!  For a $1 Hall sensor I will stick to
rolling my own.BYOM  (Bring your own magnet!)

Dave DULEY

1998\01\16@232613 by Mikal Hodvik

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Dave,

There is a common type of Hall sensor that *will* detect gaps in an iron or
steel rotor, e.g. a gear. The sensor assembly includes a permanent magnet to
bias the Hall device.

Mike Hardwick, for Decade Engineering
In Oregon, Land of Magnificent Stumps
spamBeGonedecadespamKILLspamworldnet.att.net ~ http://www.decadenet.com

>A hall effect sensor won't detect a disk with a notch cut out of it.  An
>optical interupter sensor will.  Hall effect sensors detect magnetic fields.
>You could simply strap a good rare earth magnet to the crank shaft and detect
>that with a Hall sensor.  They do that for auto trip computers.  I designed
>one about five years ago.  We had a magnet held to the drive shaft by two
>cable ties.  Worked OK.

1998\01\17@160428 by Bill (WL) Boulton

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At 08:27 PM 16/01/98 EST, you wrote:
>Bill
>Its DULEY  not DUDLEY

Sorry. Thought it was a typo. (very red face)

>All the original post said was Hall effect sensor.  I have used the
Interupter
>type hall sensors.  They are very expensive!

Not Hall effect. I am suggesting what nobody seems to have considered for
that diesel boat engine and that is an INDUCTIVE (reluctor) type. Been used
since the '60s on European vehicles. Got to be some cheapies at wreckers or
from after market auto suppliers. The nice things about them are 1) they
work in horrible filth, 2) don't need the tight clearances of Hall sensors,
3) no power required (2 wires) and 4) they're built to last. On this one,
you really can "Roll Your Own" if you want to. I wouldn't.

Bill

BTW. I've read the specs on sorta similar units from RS & Farnells and they
are deffinitely not in the same class. Low sensitivity, expensive & fragile.

1998\01\17@200119 by DREITEK

picon face
In a message dated 98-01-16 23:27:05 EST, you write:

<<
Dave,

There is a common type of Hall sensor that *will* detect gaps in an iron or
steel rotor, e.g. a gear. The sensor assembly includes a permanent magnet to
bias the Hall device.

Mike Hardwick, for Decade Engineering
In Oregon, Land of Magnificent Stumps
.....decadespam_OUTspamworldnet.att.net ~ http://www.decadenet.com
 >>
I know.  I have used these before.  They are quite expensive.
The original post just stated a Hall effect sensor.

Dave

1998\01\19@120402 by Graham, Peter

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part 0 1555 bytes
> Hello Peter,
> A hall effect sensor won't detect a disk with a notch cut out of it.
> An
> optical interupter sensor will.  Hall effect sensors detect magnetic
> fields.
> You could simply strap a good rare earth magnet to the crank shaft and
> detect
> that with a Hall sensor.  They do that for auto trip computers.  I
> designed
> one about five years ago.  We had a magnet held to the drive shaft by
> two
> cable ties.  Worked OK.
>
> Sorry to be nit picky
> Dave Duley
>
Hi Dave

Sorry to be nit picky, but it will. How do you think that a lot of OEM
or after market engine control modules work. They have a disk with
multiple notches, (dependant upon the number of cylinders and the
degrees accuracy needed) mounted to the front of the crank shaft.

They mount a Hall Effect package to sense the notches in the disk. From
what I understand the automotive package (what I suggested) has a hall
effect sensor and a magnet to give a DC field. These packages have three
leads, power, ground and output. A lot operate off 5V and give a 5V
square wave  output because of an inbuilt Schmitt trigger.

To see a hall effect used in this manner look up a data book on hall
effect sensors for either notch or gear tooth sensing or I would be
happy to email you a copy of an Allegro sensor to give you an idea of
the principle.

The easiest way is to go to an auto junk yard and grab one out of a car
with an engine control module (a late model fuel injected car).

Peter G.
TakeThisOuTpeter.graham.....spamTakeThisOuTdsto.defence.gov.au


1998\01\19@222500 by DREITEK

picon face
In a message dated 98-01-19 12:06:16 EST, you write:

<< Hi Dave

Sorry to be nit picky, but it will. How do you think that a lot of OEM
or after market engine control modules work. They have a disk with
multiple notches, (dependant upon the number of cylinders and the
degrees accuracy needed) mounted to the front of the crank shaft.

They mount a Hall Effect package to sense the notches in the disk. From
what I understand the automotive package (what I suggested) has a hall
effect sensor and a magnet to give a DC field. These packages have three
leads, power, ground and output. A lot operate off 5V and give a 5V
square wave  output because of an inbuilt Schmitt trigger.

To see a hall effect used in this manner look up a data book on hall
effect sensors for either notch or gear tooth sensing or I would be
happy to email you a copy of an Allegro sensor to give you an idea of
the principle.

The easiest way is to go to an auto junk yard and grab one out of a car
with an engine control module (a late model fuel injected car).

Peter G.
TakeThisOuTpeter.grahamKILLspamspamspamdsto.defence.gov.au >>


Peter...Peter...Peter...

A Hall efect sensor all by its itty bitty self WON'T!!!!!!
It requires a magnet to bias the thing.  OK?????

I have defended this thred long enough.  I have used enough Hall sensors to
know what I am talking about.

The original post (What seems a hundred or so years ago for those of you
recieving email by dog sled) simply stated a Hall effect sensor......NOT a
Hall effect interupter or slot sensor.  The added magnet makes all the
difference in the world.  I was simply trying to prevent some poor guy on his
boat with a 99 cent surplus Hall transistor for wasting too much time.

Enough said already.  I am related to popstal workers and I am not afraid to
use them!!!!!!

Dave

1998\01\21@203130 by Blad Cap

picon face
Me too.
Please send me a copy of the final variant.
Blad Cap
.....ustekspamRemoveMEhotmail.com

On Wed, 14 Jan 1998 15:56:58 +0200 Pasi Mustalahti <RemoveMEptmustaspamspamBeGoneUTU.FI>
writes:
{Quote hidden}

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