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  #1  
Old 04-11-2009, 01:37 PM
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Default Getting rid of PCM in Saturn

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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Last edited by Dave Koller; 01-13-2010 at 12:04 AM. Reason: more stuff added
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  #2  
Old 04-13-2009, 09:07 PM
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Default Re: Getting rid of PCM in Saturn

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.
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Old 04-13-2009, 09:50 PM
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Default Re: Getting rid of PCM in Saturn

Quote:
Originally Posted by david85 View Post
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
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Old 04-14-2009, 12:29 AM
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Default Re: Getting rid of PCM in Saturn

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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Old 04-14-2009, 12:35 AM
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Default Re: Getting rid of PCM in Saturn

PS I ran 28 miles sitting still on the odometer !! lol
Dave
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Old 04-14-2009, 01:09 AM
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Default Re: Getting rid of PCM in Saturn

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.
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Old 04-14-2009, 09:34 AM
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Default Re: Getting rid of PCM in Saturn

Quote:
Originally Posted by david85 View Post
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
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Old 04-16-2009, 01:38 AM
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Default Re: Getting rid of PCM in Saturn

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
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Old 04-20-2009, 12:41 PM
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Default Re: Getting rid of PCM in Saturn

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
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Old 04-20-2009, 08:22 PM
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Default Re: Getting rid of PCM in Saturn

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.
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