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'[PIC]: Getting signal safely from fuel injector'
2002\11\01@051155 by Impakt242

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EDIT: Sorry people, forgot to add the PIC prefix in the subject line

Hello everyone,
Now that i have decided on a PIC for my dashboard/logger circuit, i would
like to ask if anyone out there has a circuit which can interface a fuel
injector pulse signal to a PIC input?

I have found the circuit to interface it to the points, or coil output of the
car, but nothing so far for the injectors.

Can the same circuit for the points be used for the injectors? I have seen
one example on diy-efi using optocouplers, there has to be another way
though.

Te circuit would connect the injector pulses to a PWM Capture pin on the 877
to measure time high and low and show the pulse width in milliseconds, and
also show duty cycle.


Daren

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2002\11\01@062833 by Michael Rigby-Jones

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{Quote hidden}

The points interface should be very suitable.  Simmilar magnitudes of
voltage are found in injector drivers as ignition coil primaries.

Sounds like an interesting project, I was considering something simmilar to
measure fuel economy, integrating the injector open time to get amount of
fuel used and using the speed sensor to get distance covered.  Not sure how
accurate this would be though.

Regards

Mike

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2002\11\01@063309 by Impakt242

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In a message dated 1/11/2002 10:29:00 PM AUS Eastern Daylight Time,
mrjonesspamspam_OUTNORTELNETWORKS.COM writes:


> Sounds like an interesting project, I was considering something simmilar to
> measure fuel economy, integrating the injector open time to get amount of
> fuel used and using the speed sensor to get distance covered.  Not sure how
> accurate this would be though.
>
> Regards
>
> Mike

hmm to get a decent result you would need to know the fuel pressure at given
loads and throttle positions. I'll try it all out once i get the pic next
week with all the testbed gear as well :)

Anyone else have any ideas?

Daren

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2002\11\01@065032 by Michael Rigby-Jones

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{Quote hidden}

Fuel pressure accross the injectors should remain the same at all throttle
openings, that's why there is a fuel pressure regulator controlled by
manifold pressure. :o)  The major non-linearity (AFAICT) is during the
opening and closing times of the injector, which is significant for very low
and very high duty cycles.

Other ideas?  Hmm, you could use a hall effect sensor which would mean you
wouldn't even have to make an electrical connection.  Come to that you could
use inductive coupling as you are only interested in the egdes.
Opto-isolators are cheap, do you have anything in particular against them?

Mike

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2002\11\01@065447 by Impakt242

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In a message dated 1/11/2002 10:51:06 PM AUS Eastern Daylight Time,
mrjonesEraseMEspam.....NORTELNETWORKS.COM writes:


{Quote hidden}

on engines with forced induction it changes :)

I will try using the points interface, if there is no go i'll try the
optocouplers..

D

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2002\11\01@085430 by Roman Black

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Michael Rigby-Jones wrote:

> Sounds like an interesting project, I was considering something simmilar to
> measure fuel economy, integrating the injector open time to get amount of
> fuel used and using the speed sensor to get distance covered.  Not sure how
> accurate this would be though.


The fuel injector system runs at a regulated
pressure and the mechanical regulator works quite
well. Pressure deviation is close to nonexistant
as the system is designed to have sufficient overhead,
which is the easiest way to control fuel as only
injector duration needs to be considered. So YES
measuring speed, revs and injector duration should
give a very accurate fuel economy reading. :o)
-Roman

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2002\11\01@102627 by Chris Loiacono

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And why ever would you want to avoid optical isolation in this application,
unless you don't want it to last forever?

>
I have seen
> one example on diy-efi using optocouplers, there has to be another way
> though.
> Daren
>

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2002\11\01@103221 by Michael Rigby-Jones

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> -----Original Message-----
> From: Chris Loiacono [SMTP:RemoveMEchrisTakeThisOuTspamspamMAIL2ASI.COM]
> Sent: Friday, November 01, 2002 3:33 PM
> To:   EraseMEPICLISTspamspamspamBeGoneMITVMA.MIT.EDU
> Subject:      Re: [PIC]: Getting signal safely from fuel injector
>
> And why ever would you want to avoid optical isolation in this
> application,
> unless you don't want it to last forever?
>
As the millions of tachometers fitted to cars all over the world will
testify, it's not that difficult to interface a noisy, spiky high voltage
signal to a precision low voltage circuit and have it last.  An
opto-isolator is a nice simple method of level shifting and clamping in this
instance, but a simple RC network with a clamping diode will work perfectly
well.

Mike

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2002\11\01@123619 by Bob Blick

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On Fri, 1 Nov 2002, Chris Loiacono wrote:

> And why ever would you want to avoid optical isolation in this application,
> unless you don't want it to last forever?

Optoisolators in electronics are like "gotos" in C, that's why. Generally
avoidable if you know the right way to do it.

-Bob

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2002\11\01@123623 by Spehro Pefhany

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At 10:33 AM 11/1/02 -0500, you wrote:
>And why ever would you want to avoid optical isolation in this application,
>unless you don't want it to last forever?

A bit of a funny comment, since opto-isolators are one of the few
solid-state components for which aging is an important engineering
consideration.

Best regards,

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2002\11\01@182154 by Randy Jones

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Roman,

Most of the EFI port injection engines (as opposed to "throttle body" type
with a central injector) do vary the fuel pressure based on engine load
(manifold vacuum).  A vacuum signal from the intake manifold is applied to
the fuel pressure regulator diaphragm so the fuel pressure tracks with
manifold vacuum.  This causes the pressure differential across the injector
nozzle to be constant regardless of manifold vacuum.  That way, injector
fuel flow per unit of time is constant for any manifold vacuum.  This
approach makes it much easier for the engine control module (ECM) to
calculate correct fuel delivery since manifold vacuum need not be measured
and factored in.

Some newer systems are now using constant fuel pressure, and requiring the
ECM to compensate the injector pulse width for the variation in intake
manifold vacuum.

Before trying to relate injector duration to fuel consumption it would be
very important to know which system was on the vehicle.

Randy
http://www.glitchbuster.com


> The fuel injector system runs at a regulated
> pressure and the mechanical regulator works quite
> well. Pressure deviation is close to nonexistant
> as the system is designed to have sufficient overhead,
> which is the easiest way to control fuel as only
> injector duration needs to be considered. So YES
> measuring speed, revs and injector duration should
> give a very accurate fuel economy reading. :o)
> -Roman

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2002\11\02@030213 by Roman Black

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Randy Jones wrote:
>
> Roman,
>
> Most of the EFI port injection engines (as opposed to "throttle body" type
> with a central injector) do vary the fuel pressure based on engine load
> (manifold vacuum).  A vacuum signal from the intake manifold is applied to
> the fuel pressure regulator diaphragm so the fuel pressure tracks with
> manifold vacuum.


Yes I know this. :o)
I should have been more specific and said it
"keeps a constant pressure with regard to the
manifold vacuum". The effect is that the injector
pulse length controls fuel amount. :o)

> Some newer systems are now using constant fuel pressure, and requiring the
> ECM to compensate the injector pulse width for the variation in intake
> manifold vacuum.

I haven't seen this type and not real keen to
see it either. :o)
-Roman

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2002\11\02@095502 by Chris Loiacono

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Yes, as anyone who bothers to read data sheets would be aware. If it's funny
to ask the original poster a Q in order to gather information needed to
provide a useful, helpful reply....then it's also a bit funny thatI have
units in the field for over 15 years with original optos and no noticable
performance degradation. I guess it all depends on part selection and
application knowledge & experience.
While it is true that an opto emitter rated and run at 20mA will have a much
shorter useful life (also to be determined by application) the same will run
for a long, long time at 3 or 4 mA and there are many ways to get back the
high CTR & fast response as if it were run at 20.

My question was originally intended to flush out application reasons that
optos were a no-no in this project....Which apparently has yet to be shared
with the list. Is the reason cost, lack of familiarity with opto's, product
longevity, or whatever???

There is major short-sightedness in the inclusion or exclusion of a single
device or technolgy in a design based on a single parameter and an opinion
based on limited info - especially since that parameter or quality may or
may not be a real concern in the specific real-world application.

> A bit of a funny comment, since opto-isolators are one of the few
> solid-state components for which aging is an important engineering
> consideration.

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2002\11\02@100700 by Spehro Pefhany

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At 10:01 AM 11/2/02 -0500, you wrote:
>Yes, as anyone who bothers to read data sheets would be aware. If it's funny
>to ask the original poster a Q in order to gather information needed to
>provide a useful, helpful reply....then it's also a bit funny thatI have
>units in the field for over 15 years with original optos and no noticable
>performance degradation. I guess it all depends on part selection and
>application knowledge & experience.

Yes, I agree with you. Optos are the best solution in many situations..
such as high voltage level shifting and dealing with severe noise of various
kinds. As you say, reading the data sheets and *application notes* is the
key to effectively using them.

Best regards,

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2002\11\03@065554 by Roman Black

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Chris Loiacono wrote:
>
> Yes, as anyone who bothers to read data sheets would be aware. If it's funny
> to ask the original poster a Q in order to gather information needed to
> provide a useful, helpful reply....then it's also a bit funny thatI have
> units in the field for over 15 years with original optos and no noticable
> performance degradation. I guess it all depends on part selection and
> application knowledge & experience.

> My question was originally intended to flush out application reasons that
> optos were a no-no in this project....Which apparently has yet to be shared
> with the list. Is the reason cost, lack of familiarity with opto's, product
> longevity, or whatever???


Chris, I don't doubt that you have well designed
products using optos and yes the poster seemed
a bit quick to categorise as optos==unreliable.

But since you specifically asked about opto
reliability i'd like to say that optos are one of
the lesser reliable semiconductors I have come
across in the TV/VCR repair industry.

It's not the emitter that is the problem but the
photodiode, and the problem seems to apply to most
(older) single photodiodes and the photodiodes
within optocouplers. We were taught that the
silicon has to be doped to an "unstable" level to
get good photo response.

The properties of the photodiodes change over time
and are affected by voltage and current. This is
a big problem with older VCRs where the opto pairs
sensing spool rotation start to fail in an
intermittant fashion as the Vr (or Ir) of the
photodiode becomes different for the same light
level.

In the National brand VCRs it is weird as it is
always the left spool sensor that fails, even though
the right one is closer to the capstan motor and PSU
and runs hotter. BUT the left opto runs at a slightly
higher reverse current through the photodiode.

Testing them is as simple as measuring the Vr on the
photodiode with a series resistor to reg 5v, when
not illuminated, and comparing the voltage to a good
one.

The optos in TV set PSUs fail in similar fashion
slowly over time and surprise it is usually the
sets that run a slightly higher Ir through the
photodiode.

Using an opto for on/off digital use will avoid
noticing the ageing problem until it gets a lot
worse. Modern optos are a lot better too, and
designers that use a minimal Ir will get a lot
more life compared to cheap products pushing the
opto Ir to avoid using higher-gain support
components. So obviously you took the care to
design your product to last, but unfortunately
many designers don't. :o(
-Roman

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2002\11\04@080321 by Chris Loiacono

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Good points, Roman. Of course, I am always learning, and your experience is
helpful - that's the kind of depth in understanding that's needed for a
product to perform well because it's been well designed, not because all the
coins landed on heads that day. Yes, I have spent more than the usual time
with the handful of opto part numbers I have come to rely on, but there's
always more to learn. In the past I have tried a number of designs with
opto's that have failed before understanding many details. I think the point
is that opto's are at times the method of choice while at other times not.
Decisions like this can't be properly made without much application
information.

Admittedly, I've also become a bit obsessive about checking pins for things
with my new Bitscope - things I was unable to see with my old scope before,
like what happens during and following that dv/dt event from the perspective
of the MR pin. I have a feeling that, for me, this tool will change many
things for the better. At the least, it has me realizing the need not to
make snap judgements regarding hows, whys & parts. For example, I intend to
play with Sean Alcorn's book circuit because now I can watch any effects on
the PIC carefully before declaring it a good design. I'm already thinking
about load inductance......

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2002\11\04@084640 by Roman Black

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Chris Loiacono wrote:
>
> Good points, Roman. Of course, I am always learning, and your experience is
> helpful - that's the kind of depth in understanding that's needed for a
> product to perform well because it's been well designed, not because all the
> coins landed on heads that day.

My thoughts exactly. :o)


> Admittedly, I've also become a bit obsessive about checking pins for things
> with my new Bitscope
> For example, I intend to
> play with Sean Alcorn's book circuit because now I can watch any effects on
> the PIC carefully before declaring it a good design.


Well, I don't think you will be able to
declare it a good design because that circuit
connects the AC mains direct to a PIC pin
via a resistor!!! The amount of appliances i've
fixed that failed from dirty mains and most
of those HAD filters and series resistors etc.

There's no way you can convince me it's smart
to couple AC mains into a PIC pin with nothing
more than one resistor to protect the PIC.
The cost of a capacitor and zener etc are only
a few cents.
-Roman

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2002\11\04@090314 by Sean Alcorn - Avion Sydney

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Roman,

> Well, I don't think you will be able to
> declare it a good design because that circuit
> connects the AC mains direct to a PIC pin
> via a resistor!!!

Are you referring to the power supply, the zero cross detect or both?

> The amount of appliances i've
> fixed that failed from dirty mains and most
> of those HAD filters and series resistors etc.

My 80cm SONY TV died as a result of a brownout! :-)

> There's no way you can convince me it's smart
> to couple AC mains into a PIC pin with nothing
> more than one resistor to protect the PIC.

I wasn't trying to convince you, I was asking opinions. And they seem
to be widely varied.

> The cost of a capacitor and zener etc are only
> a few cents.

Again, on the zero cross detect? How would you configure it? Doesn't
the existing Zener clamp the maximum voltage at 5.6 Volts? Also, the
minimum voltage is zero volts? Can I ask you Roman, when is the neutral
ever more than 0 volts?

Again, it's not "Sean Alcorn's circuit". It's simply one of many that I
have seen using this technique.

Regards,

Sean

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2002\11\04@094851 by Sean Alcorn - Avion Sydney

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Hi Chris,

> For example, I intend to
> play with Sean Alcorn's book circuit because now I can watch any
> effects on
> the PIC carefully before declaring it a good design.

As I pointed out in another post, it's not my design, but one of Paul
Benford's. I simply posted it to know if this was the circuit that
Roman was referring to in an earlier thread. However, this is of
interest to me, as my next project will involve speed control using a
triac. I am still not sure if Roman is referring to the Power Supply or
the zero cross detection. But I have a similar, but slightly more
advanced power supply in about 6 different products, and we have
produced tens of thousands of these products without any failures. The
oldest are approaching 3 years old, and therefore far outperform older
analogue circuits we had previously. I've also seen these types of
supplies used in many reliable commercial products.

> I'm already thinking about load inductance......

Are you referring to the load switched with a triac? I will use a choke
in my prototype. I will be interested to hear what you find in your
investigations. I too have built myself a Bitscope recently.

Best Regards,

Sean

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2002\11\04@124124 by Dwayne Reid

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At 01:47 AM 11/5/02 +1100, Sean Alcorn - Avion Sydney wrote:

>As I pointed out in another post, it's not my design, but one of Paul
>Benford's. I simply posted it to know if this was the circuit that
>Roman was referring to in an earlier thread. However, this is of
>interest to me, as my next project will involve speed control using a
>triac. I am still not sure if Roman is referring to the Power Supply or
>the zero cross detection. But I have a similar, but slightly more
>advanced power supply in about 6 different products, and we have
>produced tens of thousands of these products without any failures. The
>oldest are approaching 3 years old, and therefore far outperform older
>analogue circuits we had previously. I've also seen these types of
>supplies used in many reliable commercial products.

I've been using a variation of that power supply for more than 20 years
now.  I've had almost ZERO failures.  It all comes down to the choice of
capacitor and surge limiting resistor.

BTW - the triac in that gif that you sent is shown with MT1 & MT2 reversed
- the side of the triac that the gate lead comes from should be connected
to the incoming line.

dwayne

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2002\11\04@160440 by Chris Loiacono

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> Are you referring to the load switched with a triac? I will
> use a choke
> in my prototype.
As was mentioned earlier, the inductance is a multiplier that you can use
when figuring the energy in the line transients that will occur when the
triac switches. I have a design that has a couple of years of solid running
on it that surprised me when connecting it to an inductive load. Granted it
was bound to be difficult with it's 480V pri into 1400Amp rectified
secondary.) The transients were humongous and hung up the gate opto's triac
outputs in a kind of crosstalk across phases. A single phase device will
likely perform similarly with an inductive load and more than one running at
a time.

I still like the simple circuit though and intend to play some more with it.
I like the quick low pulse for the zero-cross detect.....now if there was
only a way to detect neg or pos going....I am curious also as to how one
would figure the capacity of the power supply.

When I get to actually try this, i will share the results.

I will be interested to hear what you find in your
> investigations. I too have built myself a Bitscope recently.

The bitscope is a very cool tool, is it not....using it for the first time
was like turning on the lights after working in a dark room....
>
> Best Regards,
>
> Sean

Chris

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