Anyone using ADC for external sensor input?

[Grant]

I posted in another thread that I'm trying to use an external barometer sensor through the ADC to deal with altitude change causing large changes in fueling for a customer car

My problem is the ADC voltage is fluctuating too much.

Who else is using ADC for baro?  Or sensors?  Do people normally just use it for on/off switches? 

Here's my video:

http://youtu.be/MBMO8Ek63Ko

Please let me know if there is something wrong with the ADC chip, another firmware I should be using, or if ADC is just not supposed to be used this way. 

[MWfire]

Did you try to add 100nF-10uF capacitor to that input?

[fphil]

Also you could check your source with the voltmeter/scope set at the adc input and a good common ground

[Sprocket]

the 'fuel pressure' and 'exhaust back pressure' ADC input channels 0 and 1 are filtered already, but it depends on the spec of your box as to what is and is not in your hardware configuration

also worth reading this http://cache.freescale.com/files/sensors/doc/app_note/AN1646.pdf

If you can, use ADC channel 1, if the components are already on board.

[Grant]

Hi Guys, I believe we are using a V3.3 board.  Maybe it doesn't have a filter?  The schematic of the board shows no filter on any of the inputs.  My friend is going to build a filtering circuit for ADC input based on the filtering circuit for the boards MAP in that is already in place on the default spec.


MW,

Is the capacitor a known mod that people do?  I haven't found any info on it.

Thanks!

Grant

[Grant]

I should mention that the noise in the ADC could very easily be filtered out in the software.  The developers might want to consider having that option in a future build  ;D

[Sprocket]

Input 1 and input 2 as it is on the schematic are connected to diff 'a' and diff 'b'

the schematic is a bit shit, always has been. If you look on the top and bottom lay out you can see mcp inputs connected to op amps, those are for fuel and exhaust pressure.

[Grant]

Hey guys,

Thanks for your input from last time.

SlyAlfa took the board into his lab and added a filter to the ADC input...now the external map sensor is reading perfectly with no jitters.

The question we are having is why doesn't the load value change when we drastically change the external baro input?  We can swing it from 20kpa to 120kpa or so but the load range on the VE table doesn't change at all.

The ECU is on a test bench as the customer is some 400 miles away.  Does the engine need to be running for external baro to read?  I can upload the config if that would help. 

Here is a video I took with my thoughts at the time:

https://www.youtube.com/watch?v=50jNUD3mscE

Thank you!

[VEMS]

Hello Grant,

Baro correction is not applied to the load, but rather its a pulsewidth correction; To look at how the pulsewidth calculation modifier takes effect take a look at expression grid in VemsTune (help: http://vems.hu/vt/help/gauges/expression_grid.html). Accessible though View->Group->Calc Model. Baro correction is in the Gamma Enrichment model is applied in the Pulse Width model.

Best regards, Dave

[Grant]

Dave,

We got baro correction working, but it doesn't seem to solve our tuning limitation.   My friend posted our issues in a more recent thread.   Thank you for the reply though, very much appreciated!