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MAP sensor circuit 
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1N4001 - Signed up
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Looks like I'll jump on this one next. Fred posted about it here and it looks fairly easy.

posting.php?mode=reply&f=9&t=333

It requires a custom symbol, so I stared on that. It can come in a 6 pin or 8 pin device. Which should I go with?


Mon Jul 28, 2008 2:21 am
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I think 8 pin are most common, I haven't seen/heard of the 6 pin variant at all, can you link?

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Mon Jul 28, 2008 9:06 am
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1N4001 - Signed up
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Um the one on the left has 6 pins. Granted it's thru hole, but you can SMT it if you wanted to.

Any how, 8 pin 482A-01 case. Got it.

I'm out sick from work again, so I might make more progress on this again.


Mon Jul 28, 2008 12:56 pm
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Sorry, I see what you mean.

I meant one SMD style one for atmospheric correction onboard. You could leave room for a main map sensor in either package on there too, but people may like to leave that external to the ecu entirely. I personally would run a hose for my atmospheric readings too so I could choose a pressure neutral area on the vehicle to sample from.

An alternative would be to design a little card that itself surface mounts to the main PCB with two smd map sensors on it to make them point horizontally.

Something like this :

Image

Image

Or this :

Image

Only, perhaps mounted like this :

http://i238.photobucket.com/albums/ff26 ... 0_8613.jpg
http://i238.photobucket.com/albums/ff26 ... 0_8612.jpg
http://i238.photobucket.com/albums/ff26 ... 0_8611.jpg
http://i238.photobucket.com/albums/ff26 ... 0_8610.jpg
http://i238.photobucket.com/albums/ff26 ... 0_8609.jpg

or something

Fred.

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Mon Jul 28, 2008 1:37 pm
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1N4001 - Signed up
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Got it, so 2 sensors, one for MAP, one for ambient. Is that going to be 2 A/D's? Or will there be some way of switching between the two. I drew it up as 2 A/D's.


Mon Jul 28, 2008 8:34 pm
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Yeah, two of them, which physical format is really totally flexible, I tend to like the compact ones, especially for ambient measurement, but probably for both at the end of the day. The lack of screw mounting = more accurate readings too.

Here is the current ADC pin assignment, still subject to change, but not much. Do check before starting on the board layout and I'll review what I've done with the pins and make any final changes then.

Image

The basic idea is that each pin is hard assigned to a common function and if not being used for that can still be accessed via a programmable mechanism for any other sensor logging duties required.

We still have a few to go, but at some stage it might become feature X XOR Y for some ADC pins, or perhaps less common features will get a programmable pin like the general logging will to keep it flexible.

Fred.

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Mon Jul 28, 2008 9:37 pm
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Just curious.....
Why integrate the sensor with the board? and why MPX4250?
There are many stock sensors - especially bosh sensors used by chevy - why not use those?

I have come across about 3 instances where moisture condensed into MPX4250 sensors and altered readings.....


Tue Jul 29, 2008 3:43 am
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Post the details! Provided they are linear, accurate and 5V it doesn't matter to me :-) Any can be supported in software. How hard to get are the bosch ones though? If you provide a part number I'll tell you if I can get them here and NZ, if not, the freescale might be the best choice just for availability.

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Tue Jul 29, 2008 8:37 am
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VEMS's argument for on board MAP sensor was keeping electrical signal integrity. Something about it being the most important sensor, the need for accuracy being important. *shrug* I doubt it matters that much.

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Tue Jul 29, 2008 6:21 pm
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Fred wrote:
Post the details! Provided they are linear, accurate and 5V it doesn't matter to me :-) Any can be supported in software. How hard to get are the bosch ones though? If you provide a part number I'll tell you if I can get them here and NZ, if not, the freescale might be the best choice just for availability.


At the volumes discussed, availability is paramount.

If it is not in stock at Digikey or Farnells you will have a problem.


Tue Jul 29, 2008 7:01 pm
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