Date: Tue, 3 Dec 2013 14:18:10 -0800
Reply-To: Brett Ne <brettn777@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Brett Ne <brettn777@GMAIL.COM>
Subject: Re: Arduino and Vanagons
In-Reply-To: <CAPAEXFepCrji+XXkXQ2qBFiyK__wFeRRt+bkpdbzsPd_SqT9rg@mail.gmail.com>
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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
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