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Date:         Wed, 4 Dec 2013 21:20:34 -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
Comments: To: James <jk_eaton@hotmail.com>
In-Reply-To:  <BLU177-W347FF4AFBA02595B10B08CE0D70@phx.gbl>
Content-Type: text/plain; charset=ISO-8859-1

If I'm reading the datasheet correctly, the input pins only draw about 1 microampere, which just isn't significant and shouldn't have any impact on the ignition electronics. I would at least put a 1k resistor in series though, but mostly for protection from being handled before and during installation.

Brett

On Wed, Dec 4, 2013 at 9:07 PM, James <jk_eaton@hotmail.com> wrote:

> The actual Hall Effect sensor doesn't connect the circuit to ground; the > "Hall Effect" is about the generation of a varying voltage when an magnetic > field near a coil is disrupted by the passage of a metal surface or blade. > However, since the Hall Effect sensor drives a transistor (at least) inside > the Hall Effect sensor package, that transistor can be a 'sinking output' > or 'open drain' (boy, haven't heard that phrase in a decade) that connects > to ground. > > Sorry, electronics geek coming out. Most of us don't separate out the > Hall Effect sensor from the actual package it's part of on the > distributor. But it's why some kinds of Hall Effect sensor (packages) > connect to ground, and others supply drive signals or drive current. > > Maybe over Christmas I can get some readings for us. Having an op-amp in > the input is just going to be generally a good idea, for the longevity of > the sensors in our Vanagons. > > James > Ottawa, ON > > > Date: Wed, 4 Dec 2013 20:07:02 -0800 > > > From: brettn777@GMAIL.COM > > Subject: Re: Arduino and Vanagons > > To: vanagon@GERRY.VANAGON.COM > > > > Yah, whenever I take a measurement with a microcontroller, I take several > > readings and average them. In this case, I measure the time in > > milliseconds for 8 pulses and then calculate the engine speed. By > > unstable, I mean the rpms were mostly jumping around 1300-1800 and > > occasionally over 2k. My ear and the tach on the dash agree that the > speed > > was pretty steady at about 1100. > > > > I drug out my laptop & USB scope today and got a quick reading. Here is a > > link to a screenshot: > > https://dl.dropboxusercontent.com/u/4930890/testvan1.bmp > > > > Kind of a hybrid square/sawtooth wave form. The peak voltage is 2.82 v, > > while most of the flat part is around 2.4v. For the Arduino, that puts > the > > entire peak region below the minimum 3v required to guarantee a positive > > reading. I'll probably have to add an op-amp to buffer and raise the > > voltage a bit. I was in a hurry & now wished I had stretched out the time > > scale to see the noise on the peak region better. If that noise is right > > near the pin's high/low voltage reading cutoff, it could be causing > > multiple readings and throwing my measurements way off. If I run a > voltage > > doubler using an op-amp(with high rail of 5v), the entire peak would be > > over 4v, and then trigger on the drop to zero, I should get a pretty > clean > > signal to work from. > > > > The duty cycle is at 70%, so the shorter off cycle corresponds with the > > smaller gaps in the slotted distributor shield thingy, which lends > credence > > to > > Ryan's remark that most Hall sensors are open drain. That means that the > > Hall sensor connects the circuit to ground (drain) when in the presence > of > > a magnetic field, but opens the circuit (disconnects it) if there is no > > magnetic field. The electronic ignition feeds it a small amount of > current > > at 5v, and when the slot rotates near the Hall sensor & exposes it to the > > magnetic field, the sensor connects that tiny current to ground, dropping > > the voltage level to zero. > > > > I'll try adding an op-amp to the circuit in the next couple of days & see > > if I can get a reliable tachometer out of it. > > > > Also, there is no guarantee that a vanagon Hall sensor has the same peak > > values as the VW Fox Hall sensor that I'm using, so it would be really > > great if someone could get a scope reading on an actual Vanagon engine to > > compare. > > > > > > Brett > > > > > > On Wed, Dec 4, 2013 at 3:47 PM, Jim Akiba <syncrolist@bostig.com> wrote: > > > > > Also keep in mind the disty output is very unstable just because of > > > the slop in the gear drive/powerpulses as it's rotating. I saw the > > > same thing when we built our distributor replacement (replaced the > > > stock hall sender with a better square wave output hall sender) and we > > > saw this slop in the readings. Our pickup was given 72 pulses per rev > > > of the disty so I had lot's of granularity to see it and it needs some > > > filtering to be used for any real accuracy (like how we were using it > > > for fueling and spark control). But just rpm readings though you > > > should be good with some averaging. > > > > > > Jim Akiba > > > > > > On Wed, Dec 4, 2013 at 4:09 PM, Craig C Forney <craig@opus.com> wrote: > > > > David is right. Multiply pulses per second times 30 to get engine > RPM. > > > 30 > > > > pulses is 900 RPM. > > > > > > > > Target Vanagon idle RPM is 880 plus or minus 50, which is 29.33 > pulses > > > per > > > > second plus or minus 1.67 pulses. > > > > > > > > ICUs working properly typically perform at 850 to 910 RPM, with most > > > > performing at 860 to 900. > > > > > > > > Craig in Cupertino > > > > > > > > > > > > At 11:33 PM 12/3/2013, James wrote: > > > >>Distributor rotates at half crankshaft speed.... idle is 850 rpm.... > > > >>half is 425 rpm... one Hall Effect signal per crankshaft rotation ( > or > > > >>is that two per rotation...??).... nah, I'd better try to calculate > > > >>this tomorrow! > > > > > > > > One pulse per (piston @ TDC** on firing stroke) so two per crankshaft > > > > revolution. > > > > > > > > 850 rpm / 60 secs/minute = ~14 rev/second x 2 pulses/rev = ~28 > > > > pulses/second. > > > > > > > > > > > > ** Really at the fixed timing advance point which is a few degrees > before > > > > TDC on the 2.1l. > > > > > > > > > > > -- > > Brett in Portland, OR > > "Albert" '82 VanaFox I4 Riviera >

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


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