Freescale MPX4115AP or MPXM2102A altimeter

sharpie

Anyone up on converting a signal from either of these for measuring air pressure or altitude with the propeller?
Shouldn't be too difficult to read the signal, although if anyone's got a good method for converting the 5v analog signal from it to a readable level with the prop I'd like to hear it.· And some tricky math to convert it into pressure altitude and maybe using a 1620 or a sensirion to calculate density altitude would be cool too..

parsko

Sharpie,

How about hooking it up to an ADC and reading it in via serial communication? I think the math will be pretty simple, just modify the formulas at:

http://en.wikipedia.org/wiki/Air_density

Is that what you are looking for?

-Parsko

sharpie

Or if I wanted to read a digital device I could use the MS5534A or TAI8570 or similar with integrated ADCs.
I was thinking that as discussed in this thread http://forums.parallax.com/forums/default.aspx?f=25&m=115264&g=115358#m115358 we could create software adc's.. Did I misunderstand?

My goal is to keep part count, price and workload on the prop down to a minimum. This function is only one of MANY this project is performing, and I have a L O T of constant rs232 serial communications between multiple devices.. . I'm guessing the software ADC takes more processing power than communicating with an external ADC, but does that outweigh the extra cost?
I know all the formula's for calculating everything, my issue lies in expressing it programmatically with the propeller. I'd like to be able to enter "29.92" and it come back with the relevant info such as density altitude, temperature, humidity, dewpoint, etc... As well as be accurate as possible up to at least FL200.
I was mainly interested to hear if anyone had already done this with the prop.. or was thinking about it.

Thanks for the reply though..

parsko

I understand now. I think the software adc consumed more pins than a RS232 connection. But, yes, that is an option. I think the fastest it runs is around 80khz, which is fast enough for most any control situation.

Say, what is "FL200"?

-Parsko

sharpie

FL200 is a term in aviation for 20,000 feet. (Flight Level 200, always add two zero's to the end... FL350 is 35,000 feet and so on..).
Here's some useful info on why that's important.. http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/barfor.html
I can't seem to find a good link about it right now, but some of this math does get a little beyond the stuff I can do in my head on 3hours of sleep in two days..

I've seen stuff like what this guy did.. http://www.geocities.com/SiliconValley/Orchard/6633/projects.html
Which may be a step in the right direction, but doesn't seem very elegant, and also doesn't translate to the propeller well..(In my newbie comprehension of the chip anyway)
Or this... http://www.electronic-engineering.ch/microchip/projects/alti/alti.html
Or this... http://www.rconline.net/magazin-2000/daten-logger/daten-logger-description.shtml

None of which do what I'm looking for, and are aimed at hobby stuff.
Perhaps I should get some sleep so I can reiterate my question clearly..


-some more math
http://www.srh.noaa.gov/elp/wxcalc/formulas/pressureConversion.html
http://www.srh.noaa.gov/elp/wxcalc/formulas/densityAltitude.html

Robert@HCC

Dont know if this applies to the propeller, but take a look at this as well:

http://www.phanderson.com/stamp/wx_ad.html

Atmospheric Pressure using a pair of LTC1298'S and a MPX4115 (also examples using one ADC)...

Be interesting to see how things work out for ya, please post - It would probably give me an excuse to learn how to code for the Prop [noparse]:D[/noparse]
It does go over the math pretty good tho...as applies to the stamp. There is also some code in C on a page linked from this page.

sharpie

Thanks, that does look like some useful information...
As it turns out too, I ran across these two pages that make me almost want to just go ahead with using a 1-wire adc, etc...
http://www.maxim-ic.com/appnotes.cfm/appnote_number/1796
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2919

I will be sure to post an update when I make some progress. Guess I'll go ahead and order some of these parts and at least experiment with them..

sharpie

In fact, I'll go ahead and throw this out there if anyone's interested... Some other sites I've found while looking for info...

http://www.electronic-engineering.ch/microchip/projects/alti/alti.html
http://www.rconline.net/magazin-2000/daten-logger/daten-logger-description.shtml
http://forums.basicmicro.net/ShowPost.aspx?PostID=5245#5248
http://www.qsl.net/ok2xdx/Altimeter/Altimeter.pdf
http://www.geocities.com/SiliconValley/Orchard/6633/altimeter.html
http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MPX4115

I could go on... I think I probably have enough info to go ahead and do it already...
I will post with what I end up doing and so on..