Adc Mpx4115a - 40x1

[cherub66696]

Was just wondering if anyone can help?
I just need an easy way to convert the output voltage from the MPX4115A given by readadc from the 40X1, to a simple pressure and altitude value for a weather balloon data logger.

Thank you

 

[premelec]

It helps if you tell us what that voltage signal is in min / max range and what resolution of reading you need - otherwise what's the problem? see manual for READADC, READADC10 and which pins work on your PICAXE.

 

[cherub66696]

voltage of board is 5V, read out is (when using debug) is 210 normally, not much if any variation. 8 bit res is fine, using adc0 out of the 8 on picaxe, read manuals, not really helping.

thanks

 

[hippy]

From the MPX4115A datasheet, "Vout = Vs * (.009*P-.095) ± Error", and for reading an ADC, "Nadc = Vadc*255/Vpsu", so given the reading from a READADC (Nadc) where Vadc is from Vout of the sensor, you can re-arrange the equation to get what P is. Vs and Vpsu are known by design ( possibly the same, 5V likely ).

Ultimately you will have something like "P = K * Nadc + C"

Given the equation appears to be linear you could just take two readings, Nadc1 and Nadc2, at known pressures, P1 and P2, and from those determine what values of K and C fit as a first step. I recall that was done using 'simultaneous equations' when I was at school.

From there you can plug P into an equation which gives altitude from that.

It's not clear exactly what you are asking for - A "how to" ( above paragraphs ), how to re-arrange the equations, or how to write the PICAXE Basic commands which will implement those equations.

 

[MartinM57]

The normal data logger solution is to store the raw values (ie the READADC values) in the datalogger itself and use the external software that reads the values do all the unit conversions...:
- quicker on the datalogger side
- easier on the datalogger side
- maximum precision retained etc etc

 

[papaof2]

Have a look at this thread about the Mpx4115:
http://www.picaxeforum.co.uk/showthread.php?t=8544

John

 

[cherub66696]

great. thank you, will read thru them all

 

[MFB]

cherub66696. It was surprising to read that you are based in the UK and building a logger for a weather balloon. Although such ‘near space’ activities are well established in North America (see www.parallax.com/Resources/ApplicationsContests/Science/NearSpace/tabid/567/Default.aspx) I had assumed that UK airspace was too busy for this type of amateur research. Please could you supply links to any groups/projects in the UK that I might be able to get involved with?

 

[lanternfish]

voltage of board is 5V, read out is (when using debug) is 210 normally, not much if any variation. 8 bit res is fine, using adc0 out of the 8 on picaxe, read manuals, not really helping.

thanks

re #3. You won't get much variation of readout unless the pressure changes. Make a simple pressure chamber and experiment with that. Heaps of helpful info on the interweb. Just google. Cheers

 

[cherub66696]

cherub66696. It was surprising to read that you are based in the UK and building a logger for a weather balloon. Although such ‘near space’ activities are well established in North America (see www.parallax.com/Resources/ApplicationsContests/Science/NearSpace/tabid/567/Default.aspx) I had assumed that UK airspace was too busy for this type of amateur research. Please could you supply links to any groups/projects in the UK that I might be able to get involved with?

its for my university dissertation, the pressure reading is part of the whole project, its an autonomous robot that will trace heat signatures such as cars or heat vents (idea of volcanic activity), while data logging the atmosphere and taking air samples.

 

[spong]

cherub66696. It was surprising to read that you are based in the UK and building a logger for a weather balloon. Although such ‘near space’ activities are well established in North America (see www.parallax.com/Resources/ApplicationsContests/Science/NearSpace/tabid/567/Default.aspx) I had assumed that UK airspace was too busy for this type of amateur research. Please could you supply links to any groups/projects in the UK that I might be able to get involved with?

http://www.pegasushabproject.org.uk/wiki/doku.php#what_is_the_pegasus_high_altitude_balloon_project

 

[cherub66696]

Thank you very much, will read thru.

Regards

 

[MFB]

The is also this group...

www.srcf.ucam.org/~cuspaceflight

However, this also seems to be for students only. Does anyone know of more mixed groups doing this kind of stuff?