Anyone know how to get ADC values for 0V and 5V for the mapdaddy 4 bar? Thanks

 

like the kpa and its corresponding V?

 

http://www.freescale.com/files/senso.../MPXH6400A.pdf

 

Thanks, that helps some. I'm kind of confused here, so I might get some terminology wrong. Looks like the minimum reading is 20kPa and max is 400kPa.

I'm trying to figure out my PalmLog offset and scale values. The manual doesn't explain it for the MAP sensor. It does explain it for the WB sensor, but there seems to be differences.

Offset is easy enough; looks like it's 20 from the datasheet you linked.
I'm THINKING that the calculation for scale for the MAP sensor is
In this case, (400-20)/255 = 1.490


For the WB calculation, it's expressly stated in the Palm Tune manual

 

What do you mean by Total ADC? Thats the part I dont follow.

 

Well, if I understand it correctly, the ecu converts a 0-5V signal value from a sensor from voltage to a corresponding ADC value. The ADC values range from 0 to 255. So the ecu matches a linear signal to one of 256 values.

There's something else going on... I just am not finding it.

 

You just need the slope? Thats what it sounds like.

 

1.49 is correct, ie 1 ADC step = 1.49kpa, so 100 ADC raw value = 149+20 = 169kpa, 255 raw ADC = 379,95+20 =~ 400kpa.

Jim

 

Thanks Jim, that is what I was thinking. BUT here's the kicker. The default values for the standard 2.5 bar sensor are offset 9 and scale .984
(250-9)/255 = .945 =! .984


The 'real world' difference may only mean a couple kpa, but still.

 

You can't change the scale in the software for the 400kpa sensor?

 

The scale is set by the sensor--I'm trying to tell the software what that scale is for my given sensor.

One would think the relationship is linear, and a simple y = mx + b equation would be appropriate.

 

I understood that the sensor sets the scale, reread my question. I take it that there isn't an option in the software than to tell it what the scale is. The relationship is linear. On the datasheet there is a graph of Vout vs. KPa. On the top left it shows the formula for finding Vout. Just multiply Vin into the part in parentheses since you know it to be ~5V. As for modifying stuff for scale I'd need to see the software, and from looking at website I need a palm pilot to do that. I might be able to scan the source code if its well commented, but I don't have the right software to recomplie it if I found the variable that needed changing.

 

It looks like the complier suite the guy used has a free trial, I'll check it out once I get home from my adviser meeting.

 

Yes, you do enter the scale into the software. The software gets 2 variables:
the offset or minimum value "b"
the scale or slope "m"

I'm trying to figure out how the guy who wrote the software got a slope of .984 for the stock 2.5 bar, when the logical solution is .945. Then, I can apply those findings to settings for my 4 bar.

 

I would just account for it as computational error. Best bet it to email the guy if you want to know what he did. All I can do is guess.

 

I doubt it's computational error. I messaged the creator of the software in the Palm subforum at MSEFI.com.

 

The default offset for the MPX4250AP is 20 and not 9, check the Freescale Datasheet. Maybe his specific part deviated a lot (check the % of deviation chart).

Jim

 

Yeah, that's interesting. As is my kpafactor.ini for the 4250 shows that it's 11.

Unfortunately, I can't find a kpafactor.ini for the 6400 that shows output vs adc ??

I have 11 and 1.49 plugged into the palm as offset and scale respectively. it seems to be accurate with the engine off, but off by 2-3 kPa high at idle. Can't really drive and compare between the laptop and palm.

 

Hey Ben; do you think the values I used for the regular sensor are off? I wouldn't be surprised...I don't think I screwed with them; I think I just left them as default (assuming default was for standard sensor).

 

yes, I think that the default values for the 2.5 bar are incorrect. but the calculation only affects the map display on the palm; it does not affect anything when your computer compiles the datalog.

I would probably try offset 11 and scale .937
I got those values from my mapfactor.ini file for the 2.5 bar sensor.

I wish I could find a mapfactor file for the 4 bar sensor. I'm kind of confused that I can't.