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Thread: Odd behavior - Gear voltage levels are not stable Reply to Thread
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  Topic Review (Newest First)
04-13-2012 06:48 AM
Voltar Glad it worked out !
04-12-2012 10:27 PM
BigMan73
Good update

I just finished a test ride, after installing the new military precision resistors (for the gear position sensor voltage divider).
The reading are super accurate, and even though I did not ride much, and the temperature did not change too much, gear reading are rock solid!
NO FI codes
I used 2 X 499K Ohm resistors (CMF55499K00BEEB),

I also installed the DS18B20 temperature sensor in the front box (where the LCD is), so now I have two temperature readings: One which is true ambient air temperature, and another which is the Arduino's on board temperature. I like it.

I got two more military spec resistors for the battery voltage divider but am too lazy to install them, since I need to remove the existing resistors - a lot of clean up work.. next week.

@Voltar: If you decide in the future to have voltage dividers, e.g. for measuring the battery level, please remember my advice/lesson - For ADC ALWAYS use high precision, low PPM/K metal film resistors..

Thanks everybody for helping out!!
I will do more test rides in warmer days, and hopefully can keep reporting a stable solution.
04-09-2012 11:53 PM
Voltar Big:

I am sure I exactly understand the circuit of the ECM wire going into your ADC input. Have you post the simple schematic?

That said, Rs in paralleled do yield a smaller R. It is logical because current now has multiple paths to follow instead of one. More paths for current = less resistance.

Then from Ohms law we also know that as R gets smaller, V will also get smaller (given the same amount of current).

Does that help or am I stating the obvious?
04-08-2012 08:28 PM
BigMan73
Quote:
Originally Posted by Voltar View Post
Big:

Two things....

- I think the larger resistors are need to reduce the loading in the ECM or else the FI light will come on as to overload the output.

- don't forget that in "N" the ECM has to drive a green neutral light as well.

Hope that helps some.
Thanks - After some thought:
The ECM resistor (i.e. R1 - from GPS to GND) and my resistors (i.e. R2) are in parallel.


This resistor calculator is very handy:
Parallel Resistor Calculator R1 + R2 = equivalent resistor R resistance equiv total resistor finder - sengpielaudio Sengpiel Berlin

It shows clearly that R2=20KOhms with any value of R1 greater than 20KOhm will always result in a value smaller than 20KOhms.

But why does the voltage go down? I think the ECM measures voltage on the R1, and if there is less resistance on R1, R1 is less dominant to R[GPS] and therefore the voltage on R1 goes down.

What do you think? Makes sense?
04-08-2012 08:19 PM
Voltar Big:

Two things....

- I think the larger resistors are need to reduce the loading in the ECM or else the FI light will come on as to overload the output.

- don't forget that in "N" the ECM has to drive a green neutral light as well.

Hope that helps some.
04-08-2012 07:01 PM
BigMan73
Quote:
Originally Posted by greywolf View Post
I only have a rudimentary knowledge of this stuff. It would seem to me the FI comes when the voltage read exceeds 0.2V and resistance added in parallel reduces the overall resistance, possibly allowing the voltage to increase beyond spec.
The voltage actually came down by 0.4V and the FI appeared only when I was in N gear. I guess the ECU expects some predefined range (just like my firmware does) and when it doesn't get it right it complains..

EDIT:
These are the resistors (2 are needed) I'm thinking of getting now (900KOhm, 0.1%, 25ppm also military spec):
http://www.mouser.com/Search/Product...y71-RN55E9003B
04-08-2012 06:48 PM
greywolf
Quote:
Originally Posted by BigMan73 View Post
But why is the ECU so picky about 20KOhms in parallel to to the GPS line??
I only have a rudimentary knowledge of this stuff. It would seem to me the FI comes when the voltage read exceeds 0.2V and resistance added in parallel reduces the overall resistance, possibly allowing the voltage to increase beyond spec.
04-08-2012 06:33 PM
BigMan73
Have some insight!

I am not a person that gets discouraged quickly.. for better and worse, mostly the later :mrgreen:

Took some time to clear and arrange my thoughts and but I got back my to a scientific & methodical approach - experiments.

First, I disconnected the Arduino/Stromputer completely in order to try and determine if it is the Stromputer's fault or the voltage divider as a concept.

I performed 3 experiments:
1. I took a breadboard and built on it a voltage divider with 2X500KOhm resistors. No FI code.
2. I then built another voltage divider with the Military spec 2X10KOhm resistors (I got 4 - 2 were used in the Stromputer, I used the 2 other).
FI Code happened! Hmm. Interesting find - so it has nothing to do with the Stromputer.
3. Then I wanted to determine if the Mil Spec resistors are causing issues or it is the resistance value. So I used two 'simple' 10KOhm resistors (the DIY type with color codes and 10% tolerance)
FI Code repeated! So it was the resistance value!!

But why is the ECU so picky about 20KOhms in parallel to to the GPS line??

Interesting note - when I had the FI Code, and I pulled the clutch lever there was a low volume but repeatable buzz from the ECU's area. As if there a small buzzer there?!?

(Between each experiment I turned off the switch, to clear the FI code)

I guess I need to go back and buy 500KOhm (or larger) military spec resistors. Not a big deal, about $4, just a bit annoying. I guess this is the learning price I have to pay.

Will update you all once I fix this issue. GreyWolf - Thanks for the mental support!
04-08-2012 02:50 PM
BigMan73 Another idea - What if I put a diode on the gear wire? It should reduce the voltage by 0.3V-0.7V (depending on the diode type) and therefore reduce the incoming voltage.
04-08-2012 12:04 PM
BigMan73
Quote:
Originally Posted by greywolf View Post
See FAQ: Dealer Mode & FI Error Codes on FI checking. Chances are you are getting a c31 gear position sensor failure, switch voltage is out of the specified range. The range is greater than 0 but less than or equal to 0.2V.
Didn't get the FI Code, but ou're probably correct.
So I guess my board is dropping the gear voltage somehow, I do see a drop of 0.4V in my voltage tester - just I don't understand why and how this could happen.
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