You need an input buffer followed by a voltage clamp.

Perhaps...I'll know more once I get a good shot of the pulse shape on a
scope.  And I'm assuming that the 89 Fox Hall sensor behaves closely to the
Vanagon Hall sensor.  I'm still surprised by how weak that signal is; you'd
think they'd need a shielded wire, especially being so close to the high
tension ignition wires.

Brett

On Tue, Dec 3, 2013 at 3:08 PM, Thomas Hargrave <tphjr@hiwaay.net> wrote:

>  You need an input buffer followed by a voltage clamp.
>
> Tom
>  ------------------------------
> From: Brett Ne <brettn777@GMAIL.COM>
> Sent: 12/3/2013 4:18 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Arduino and Vanagons
>
> Just a quick update.
>
> I bludgeoned together an Arduino program to calculate and display the
> engine speed based on the Hall sensor output(my programming "style" makes
> hackers' code look elegant).  To deal with the presupposed high voltage(to
> a microcontroller, anything over 5v is high voltage) from the Hall sensor ,
> I put a 10k and a 3.3k resistor in series with one end connected to the
> Hall output and the other to ground.  The Arduino input pin was connected
> between the two resistors, which should give a voltage output of 1/4
> whatever the voltage is coming from the Hall sensor.  I tried hooking it up
> a couple of times with the engine running and it stopped it cold
> immediately each time.  That is one *weak* signal!  A 13.3kohm path to
> ground shuts it down.  Just to live life on the edge, I removed the 3.3k
> resistor going to ground and tried again.  This means that the full voltage
> coming from the Hall sensor will be going to the Arduino input pin(it's
> only $2-3 for a new chip if I burn out the pin).  This time, the engine
> continued running without complaint and I was getting rpm readings on the
> LCD.  WooHoo!  The readout was too high and very unstable, so there is
> still much work to be done in this first step.  I'll have to recheck my
> code; my formula was based on timing 8 pulses, but I may have set the
> counter wrong and it's counting only to 7 pulses, giving a higher than true
> reading.  I think the the instability has to do with the handling of a very
> weak signal.
>
> Sometime in the next day or two I'll drag my laptop out and hook up my USB
> oscilloscope to it and get a better idea of what this Hall sensor output
> looks like.  Because the Hall signal is so easily disrupted, It looks like
> we'll need to add an op-amp voltage buffer in order to be able to use this
> signal without affecting the ignition system.
>
> This gives yet another option for those thinking of installing a hidden
> vehicle disabling system for security.  Tie in a wire to the Hall output,
> run it to a hidden toggle switch that switches it to ground via a 5k
> resistor.  Less obvious than a fuel relay disabling system.  It'd take a
> good mechanic at least a half hour to find it.  An average mechanic would
> take several hours and would have replaced the engine computer, coil, cap,
> rotor...
>
> I've started looking into the circuitry required, but am not to a stage yet
> where I think it would be fruitful to report.
>
>
> Brett
>
>
> On Wed, Nov 27, 2013 at 3:34 PM, Brett Ne <brettn777@gmail.com> wrote:
>
> > At this point, I don't know if it's worthwhile spending much more time
> > studying duty cycle outputs under various conditions.  David's provided
> > enough data to have a pretty clear picture of what the ICU is doing under
> > various idle conditions. The purpose of gathering the duty cycles isn't
> to
> > provide target values for the microcontroller to strive for, but rather
> to
> > get a feel for how much the duty cycle needs to change to compensate for
> > various loads.  In fact, I'm no longer convinced that the duty cycle
> values
> > above closed throttle position have much use for us.  Our version of the
> > ICU would quickly drop the duty cycle to zero as the throttle is opened &
> > the rpm's climb and keep it at zero until the throttle is closed to
> > decelerate whereupon the duty cycle will start to increase when the
> engine
> > speed drops below the idle speed target.  We may get away without needing
> > the throttle switch input.  But then, there may be driveability issues
> with
> > that approach; there may need to be some baseline idle valve air flow
> level
> > needed.
> >
> > We will definitely need coolant sensor voltage readings at a known cold
> > value and a known hot value so we can calculate the temperature from the
> > sensor voltage.  If someone has an infrared thermometer and a decent
> > digital multimeter, that would be the easiest way to get those readings.
> >
> > Brett
> >
> >
> > On Wed, Nov 27, 2013 at 1:22 PM, JRodgers <jrodgers113@gmail.com> wrote:
> >
> >> David, glad to hear you are crawling back into the light!
> >>
> >> \John
> >>
> >>
> >> On 11/27/2013 1:45 PM, David Beierl wrote:
> >>
> >>> At 09:33 AM 11/27/2013, Brett Ne wrote:
> >>>
> >>>> A member pmailed results of some testing last night:
> >>>>
> >>>
> >>> Ok, I'll 'fess up.  I'm the guy who's been supplying numbers for
> >>> this.  I've been going through a very rough patch over the summer and
> >>> not wanting to talk to anybody, but at least for the moment this and
> >>> some other things happening here are bringing me out of my hole to some
> >>> degree.
> >>>
> >>>
> >>>  "...just checked a spare ISV using DC, operation is proportional to
> >>>> applied
> >>>> voltage.  Starts opening somewhere around 3 VDC, fully open somewhere
> >>>> around 8 VDC."
> >>>>
> >>>> So we can treat it as if it's a dc motor operating against spring
> >>>> pressure.  Keep in mind that we are feeding it a modulated signal, so
> >>>> even
> >>>> at 11.5 v and a 50% duty cycle, the valve will operate as if it's
> >>>> receiving
> >>>> a constant 5.75 v steady signal(11.5 x 50%) and will not be fully
> open.
> >>>>
> >>>
> >>> Here are some better numbers for the spare valve, which is a bit
> >>> sticky at the extremes (maybe they all are, I don't know):
> >>>
> >>> Resistance 4.0 ohms.
>
> >>>
> >>> Impedance at 150 Hz (sine wave) using a signal generator with 50-ohm
> >>> output: 1.0 Vrms --> ~25 mA so ~40 ohms.
> >>> Impedance at 1000 Hz ditto: 1.0 Vrms --> ~9 mA so ~110 ohms.
> >>> My generator couldn't maintain a square wave while driving the valve
> >>> because of its higher output impedance (result was a set of spikes
> >>> with smoothly declining tails) but the numbers at 150 Hz were similar.
> >>>
> >>> I may be able to hook up an amplifier to the generator and actually
> >>> drive the valve at operating levels, but in the meantime, using a DC
> >>> supply with max 1300 mA output:
> >>> On increasing voltage valve jumps open slightly at about 2.4V / 500 mA.
> >>> On decreasing voltage valve closes at about 1.5V / 325 mA.
> >>> On suddenly applying 6.5V / ~1300 mA valve snaps fully open.**
> >>> On suddenly applying 5.8V / ~1100 mA valve does not fully open.
> >>>
> >>> **The open-circuit voltage is probably somewhat higher since I'm
> >>> driving the supply at its current limit here.
> >>>
> >>>  So lets crunch some numbers to see what's going on during cranking.
> I'm
> >>>> going to calculate the power (watts) going to the idle valve during
> cold
> >>>> idle and during cold cranking and compare.
> >>>>
> >>>> First, let's calculate the resistance that the idle valve provides so
> >>>> that
> >>>> we can determine current flow for different voltages.  We know that at
> >>>> 9v
> >>>> and 29.4% duty cycle the valve draws .157 A, so we can get amperage @
> >>>> 100%
> >>>> duty by dividing .157/29.4% = .534 A.
> >>>> Resistance = Voltage/Current = 9v/.534A = 16.85 ohms of resistance
> >>>>
> >>>
> >>> Actually you can't extrapolate to DC this way because the valve is
> >>> highly inductive.  As your duty cycle approaches 100% the valve
> >>> effective impedance will get closer and closer to its four ohm
> >>> resistance.  If I can get the amplifier hooked up and delivering some
> >>> approximation of a square wave I'll be able to vary the duty cycle
> >>> directly and provide more numbers.
> >>>
> >>> Also bear in mind that the 6V/9V/10-11V numbers I supplied for peak
> >>> voltages in the system while operating a) are very approximate,
> >>> eyeballed off a tiny pocket oscilloscope screen at two volts per
> >>> division and b) need to be increased by about a volt each because the
> >>> baseline was about a volt negative.  The ~10-~11 range was
> >>> immediately after starting vs after running a few minutes; probably
> >>> because B+ was recovering after extended cranking with the ignition
> >>> disabled.
> >>>
> >>> Vrms and duty-cycle numbers are from a fancy 4-1/2 digit Fluke meter
> >>> with flat response well above our frequencies of interest and IIRC
> >>> four measurement cycles per second.  If I indicate a ~n.whatever on
> >>> one of those readings it's because it's fluctuating.  You shouldn't
> >>> use any more decimal places in calculation than the least that I
> >>> provide (i.e. if I give you ~9 for an input, a calculation from that
> >>> resulting in n.nn has to be trimmed to ~n to be meaningful).
> >>>
> >>> The white wire on the ISV is less than an ohm to the alternator case,
> >>> so you're right that it's grounded.
> >>>
> >>> Duty cycle at a cold start at 60F ambient was down to around 23% by
> >>> the time I could leave the front of the van, walk through the house
> >>> to avoid the soaking wet cedar tree and reach the back.  Quickly got
> >>> down to 21% or less.  I don't think I've yet seen it below 20%.
> >>>
> >>> I've not yet been able to catch the duty cycle for the short
> >>> excursion above 1000 rpm that happens a few seconds after a cold
> >>> start.  But I think a more important number is the rpm reached
> >>> (guessing 1100) and duration and how this is affected by
> >>> ambient/engine initial temp.  And is this normal system behavior or
> >>> an oddity of mine?  Like the short period above 1000 when I idle down
> >>> while driving, it's consistent among different ECUs both 022D and
> >>> 022F, but unknown if consistent among different ICUs since I have no
> >>> spare.
> >>>
> >>> Playing with the throttle plate as it was beginning to warm up it
> >>> seemed to vary between about 22-24% without any particular systematic
> >>> behavior.  It's hissing down with rain so I'm not going to wait for
> >>> full warmup at this point.  I think the  changes are some artifact of
> >>> system operation and don't matter.
> >>>
> >>> Stabbing the throttle produced slightly wider variations up to maybe
> >>> 20-25% but I have trouble seeing how it can matter given the input
> >>> from the driver's foot swamping everything else.
> >>>
> >>>  This was quite surprising to me; the power going to the idle valve is
> >>>> less
> >>>> during cold cranking than during fast idle.  I was thinking that it
> >>>> would
> >>>> receive more power during cranking to get a good supply of air & fuel
> >>>> into
> >>>> the engine to really get things going.  Then I thought maybe it's
> >>>> trying to
> >>>> restrict the air a bit to richen the mixture, but the ECU knows when
> the
> >>>> engine is cold cranking and fuel mixture is one of its main jobs.
> >>>> Maybe by
> >>>> restricting airflow, it effectively lessens the compression ratio to
> >>>> make
> >>>> starting easier.  Or maybe I'm just overthinking this and it's trying
> to
> >>>> put out the same airflow as cold idle but isn't able to accurately
> >>>> make up
> >>>> for voltage drop during cranking.
> >>>>
> >>>
> >>> I suspect the last.  It would be answered by doing cold cranking with
> >>> a booster to keep the voltage up, but I'm not equipped to do that
> >>> (though I'm probably going to have to replace the tired battery soon
> >>> if I want to drive at all this winter).  This engine has always
> >>> seemed to crank hard since I've had the van, and replacing the
> >>> starter didn't change it.  Sometimes it cranks fine and sometimes it
> >>> goes to its knees on the first revolution, then recovers.
> >>>
> >>>
> >>>  I think that it would be best to aim for the same airflow for both
> cold
> >>>> idle and cold cranking and adjust as real world results suggest.
> >>>>
> >>>
> >>> I think that's sensible.
> >>>
> >>> Yrs,
> >>> d
> >>>
> >>>
> >
> >
> > --
> > Brett in Portland, OR
> > "Albert" '82 VanaFox I4 Riviera
> >
>
>
>
> --
> Brett in Portland, OR
> "Albert" '82 VanaFox I4 Riviera
>

--
Brett in Portland, OR
"Albert" '82 VanaFox I4 Riviera