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#### Dave Koller

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GO to last pages for new STUFF!!

>>>>>>>>>>>>>>>>>>>>>>>>>

I edited this opening as it contains other things at the end than about the PCM... hope it is helpful!

Tachometer at the end added 11/22/09 ------------

I have been working on getting rid of the PCM in a 1999 Saturn Sl2. Bypassed the Tachometer on atzi's 1998 Saturn... http://www.saturn.offical.net/node/326
So now it is on to the speedometer. I used a Heathkit (yep, I have one!) function generator
to send a pure sine wave to the PCM... I settled on 60 MPH as this is the most important one to use - as it represents 1 mile per min or according to the output in all the manuals I could find the Speedometer = 5000 pulses per mile (thus per min) .. What is strange is all the information I can find says Saturn VSS has 10000 pulses per mile (ppm) so at 60 mph I should have 10000 = 1 min and 10000/60 = 166.66666 HZ... right?
But I get 230 HZ for 60 mph !! that equates to 13800 ppm (VSS sine wave NOT square wave to speedometer) . SO if that is true then there is a strange number to divide by to get the square waves for the speedometer ! 13800 / 5000 = 2.76 .. not the best number to digitally divide by !!

So it does a bit of strange processing NOT the simple divide by 2 that 10000ppm would get me !

The formula I use to get MPH from the sine wave is ---[ MPH x 13800 / 60 /60 = HZ] or 60 x 13800 = 828000 /60 = 13800 /60 = 230 Hz..
Easier to see a different one:
30 (MPH) x 13800 (PPM) = 414000 /60 (min) = 6900 /60 (sec) = 115 HZ (or cycles per sec)
AND YES 115 hz gives me 30 mph!!

I thought I would throw this out to see what others think! Perhaps they phase lock it at some frequency but not sure!

Dave

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#### david85

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Great work! I'd like to toss the PCM in mine too, but I really want to be able to keep the OEM tach and speedometer.

#### Dave Koller

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Great work! I'd like to toss the PCM in mine too, but I really want to be able to keep the OEM tach and speedometer.
I have found out much more and will post more pics with scope shots crazy way the PCM figures from VSS - thought it might be a straight algorithm - can't tell if it uses a PLL or just filters with division......
Dave

#### Dave Koller

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Used a safety pin into D6 connector Pumped 230 hz sine wave in to the VSS input...

Got 60 MPH MPH OUT AND 84.32 HZ out of PCM!!

SCOPE:
230 HZ SINE (bottom) in .............. 84.32 perfect SQUARE WAVE OUT(top) !!!!!!!! 5000 (ppm that manual says) /84.32 = 59.29 MPH
(close enough)
Figure the meter is off a few HZ and it comes to 5000ppm / 60 sec = 83.33333 my original math for factory!!!

So what the heck is 230 HZ in ? 230 / 84.32 = 2.7277039 aprox ....

Two things still wrong here - the ratio of 2.7 and how the heck are they getting the division ? well I need more work there... Have discovered a pure sine is clean but under noise of EV motor it introduces more pulses -- this opens up a whole new area of RF Noise besides our radios

Dave

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#### david85

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The VSS puts out a different frequency than the PCM? Why the heck would they do that? Seems to me like it only complicates things.

#### Dave Koller

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The VSS puts out a different frequency than the PCM? Why the heck would they do that? Seems to me like it only complicates things.
The PCM will compensate for various gear ratios, tire size, maybe models, but why I am getting what I am does not relate to what is in certain manuals.. I have run across 10000 ppm for GM and Saturn FROM VSS - that would be nice as it is 2 to 1 (5000 ppm) - easy to convert the sine to pulse at one half frequency with single flip-flop........

http://ecomodder.com/wiki/index.php/MPGuino

scroll down to chart on various cars......

If anyone has more info on VSS from Saturn - jump in here

Dave

#### Dave Koller

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Well quick thought... using a PLL like a 4046 locked to 4 X 230 HZ (sine for 60 MPH) out of VSS then divided by 11 (non fraction - my 2.7x X 4) gives 83.xxxx square wave that divided into the 5000 ppm will give me 60 MPH - well close enough!! I will make that and post some info.....

So since my Saturn only needs the PCM for Speedometer and Tach it looks like a couple of chips can do the job... Now on to interfaceing the temp gauge with pulse width modulation from a thermistor input .... Still no ideas out there?

Dave

#### Dave Koller

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Well a PLL of 230 X 100 then divided by 276 will yield the 83.33333 for the 60 MPH on the speedo.... going to make it in components as a pic or Ardunio processor will not output the exact numbers I need... It will be more accurate than the PCM as it will also have a filter system for extreme noise! Both my speedometer and tach will run seperate from all the other things I want to do! I intend to use ALL the idiot lights (of course I will replace them with LEDS! ) out of my own processor and all the temperature sensors, inputs, I can make do other things... OK so we shall see!!!! Be it warped - I still have a sense of humor ...

Dave

#### david85

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I'm sorry we don't have anyone else here that can contribute much to your thread, but I am following it. Please keep up the good work.

I actually toyed with the idea of putting "idiot lights" at the front of the dash panel where it sweeps upward. The idea being to copy the look of the EV1.

#### Dave Koller

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I'm sorry we don't have anyone else here that can contribute much to your thread, but I am following it. Please keep up the good work.

I actually toyed with the idea of putting "idiot lights" at the front of the dash panel where it sweeps upward. The idea being to copy the look of the EV1.
It is ok -- I see a lot have been looking... when I add my own processor, it speaks and shows SOC on the fuel gauge and temps on the temp gauge ( and a small screen ) it may spark a few points to converse with some... I have "lurked" around a bit myself and watched others do some really different things....

Dave

#### Sega

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Hey, could you please tell me where you located that D6 connector for the speed sensor? I've looked through my Saturn and I can't find it.

#### Dave Koller

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Hey, could you please tell me where you located that D6 connector for the speed sensor? I've looked through my Saturn and I can't find it.
What year do you have and where is your PCM located.. I assume you are referring to the pickup for direct tach as on

http://www.saturn.offical.net/?q=node/304

or are you looking to find the speedometer pickup on the transaxle?

Dave

#### Sega

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I am looking for the speedo pickup. I'm (gradually) making an EV1 inspired dash but I've spent a few hours without luck looking for the speedo sender (found switch 12v power and ground easily). This is a side track from my EV conversion of course.

#### Dave Koller

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I am looking for the speedo pickup. I'm (gradually) making an EV1 inspired dash but I've spent a few hours without luck looking for the speedo sender (found switch 12v power and ground easily). This is a side track from my EV conversion of course.
If you have a saturn it should be on the transaxle case... blue top and a purple and yellow wire to the PCM...
Dave

#### david85

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I'm (gradually) making an EV1 inspired dash

#### Sega

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Yup, and will do. It'll take a while, especially because the speedometer I got on ebay doesn't display in Kilos which is what I drive in, so I probably won't use it. I found the speed sender cables, thank you Do you know of any in the plug that connects to the instrument panel directly? I'm going to tinker with it tomorrow, and if that fails I'll run wires off the sender you showed me.

#### Dave Koller

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I found the speed sender cables, thank you Do you know of any in the plug that connects to the instrument panel directly? I'm going to tinker with it tomorrow, and if that fails I'll run wires off the sender you showed me.
Still not clear on your car and model - year - all that makes a difference....

Dave

#### Sega

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My bad, it's a 2000 SC2. My Haynes manual doesn't help much with the dash wires.

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