Dose anyone know where the equation for altitude from pressure on page 14 of the data sheet came from? When I ask the sensor for the pressure and then calculate the altitude using on-line calculators I get my altitude. When I use the equation (or let the sensor use the equation I get the same result but its way off from my actual altitude 196m (sensor) vs. 262m (from map)

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Hello Sparkfun folks,

Working on building an altimeter that collects the highest reading and displays it on a seven segment display for students in a middle school science class who are building soda bottle rockets. I've got pretty much everything going well but when I got this set up with the example Altimeter code provided by Sparkfun I'm getting some off readings. My temperature is actually close to perfect (reading 63.5 F which is only 1 degree off from my thermometer in my room) but my altitude is reading in a range from -120 to -70 without me moving the sensor at all. My actual altitude is around 400.

Any suggestions as to what might be going on? I've heard some people say I should run some sort of calibration code but I can't seem to find an example of that and I don't think I could write that myself.

Thanks!

Hello all,

I recently bought this sensor for my Arduino UNO. I am a beginner with these stuff, so some questions: 1) According to the hookup guide I need some 330ohm resistors for the I2C lines. How do they calculated the exact resistor amount to reduce 5V to 3.3V? I will like some theory here. 2) Do I need these resistors if I am only connecting this sensor in the UNO (I don't have other breakout boards)? or I will burn the breakout without them?

Thanks

I have two of these pressure sensors with each connected to a Particle Photon, the sensors are placed next to each other, I have one sensor reading 2249 Pascals and another reading 2087 Pascals. Can someone please suggest the reason for this huge difference in readings of about 162 Pascals. This equates to about 123 ft altitude difference between the two sensors.

If you plan to use this with a Raspberry Pi, be warned that this chip doesn't play nice with Raspberry Pi's I2C bus. This is due to it's use of "repeated start" in the I2C protocol (which Raspberry Pi can't handle without bit-banging).

I am not sure how I feel about this thing. With the SparkFun sketch, it says my altitude is 517 feet and the barometer is 30.21 InHg. My GPS altitude is 780 feet and google maps says I am at 790 feet and a local airport says the barometer is 30.23. It looks like the barometer is working but the altimeter is way off. Also, as stated by the datasheet this thing is pretty sensitive to sunlight. I got large fluctuations when using it. Is there a reference adjustment for this similar to how pilots set the altimeter based on the barometer?

Pressure(Pa):99479.75 Temp(f):73.40 Altimeter setting InHg:30.21 with sketch set to 780 feet Altitude(ft):517.55 Temp(f):73.29

Near KLPR; Lorain County Regional Airport http://www.flightstats.com/go/Airport/weather.do?airportCode=KLPR

Hi. I'm using intel edison and spark-fun's MPL3115A2.

And I connect this sensor to sparkfun's I2C breakout block(https://www.sparkfun.com/products/13034) for connecting intel edison.

now when I upload SparkFunAltimeter.ino, I can get some values but it is a little weird like this :

Altitude(m):-999.00Pressure(Pa):-999.00 Temp(c):-999.00 Altitude(m):-999.00Pressure(Pa):-999.00 Temp(c):-999.00 Altitude(m):-999.00Pressure(Pa):-999.00 Temp(c):-999.00 Altitude(m):-999.00Pressure(Pa):-999.00 Temp(c):-999.00 Altitude(m):-999.00Pressure(Pa):-999.00 Temp(c):-999.00 Altitude(m):-999.00Pressure(Pa):-999.00 Temp(c):-999.00 Altitude(m):-999.00Pressure(Pa):-999.00 Temp(c):-999.00 Altitude(m):-999.00Pressure(Pa):-999.00 Temp(c):-999.00 Altitude(m):-999.00Pressure(Pa):-999.00 Temp(c):-999.00

Should I check some part of this code? I've never changed this code.

actually I am really beginner for arduino code.. anyone who know how can solve that problem? Please give me any help.

Thank you in advance.

Regard.

JaeHyuk

So I got this chip for a demosat project and I can't get accurate readings from it. sometimes the values will be close other times its completely wrong and all of my wiring is correct. A lot of people have been commenting asking how to calibrate this but no one seems to be able to give any usable advice. DOES ANYONE KNOW HOW TO CALIBRATE THIS CHIP AND GET IT TO REPORT ACCURATELY!?!

Hello,

I am having trouble using this MPL3115A2 with an Arduino Fio v2 (https://www.sparkfun.com/products/10116). I have hooked it up as instructed (without resistors since it's a 3.3V board) and installed the library. The example of the library gives me obviously wrong measurements for temperature and pressure (way overestimated). I tried with a Arduino Uno and it work perfectly with the exact same parameters (setOversampleRate(x), for instance) so it's not a problem of calibration. I'm therefore guessing thats something's wrong with the I2C protocol, but I can't figure out what. Can anyone help me ?

Thanks, Rémi

How much does this weight?

Hello!

I'm having a lot of problems with getting any accurate readings. It seemed to be working somewhat using the Arduino UNO but still says I'm below sea level by about 400ft (not true). However, I needed to switch over to a Mini and have failed to get any readings at all that make any sense. I'm not quite sure how to debug - but, I've soldered wire to A4 and A5 in the middle of the mini and it appears to be cleanly connected. Right now, it is reading:

Altitude(ft):-5068.69 Temp(f):194.90

Switching back to the UNO the room temp appears to be correct, but the altitude not so much.

Can anyone give some tips as to how to get to the source of the issue here? Any known issues with using this sensor with the mini? I'm using the code sample that has been posted with it untouched.

Thank you. Claudia

I want to use MPL3115A2 with arduino YUN, So is it work properly in this case too?

I was having quite a time trying to get this to work with my Pi. Eventually I found that there is a mod that has to be enabled.

The short version:

pi@raspberrypi ~ $ cat /sys/module/i2c_bcm2708/parameters/combined
Y

The long version:

http://ciaduck.blogspot.com/2014/12/mpl3115a2-sensor-with-raspberry-pi.html

Hello!

I wired this up easily and it seems to be functioning - but the altitude reading is probably 500 feet off or so from where I know I am. I've perused the comments below but didn't find a consensus on whether this is expected or if it indicates some kind of error. Also - it may be that it needs calibration? Any input / help welcome!

Thanks!

How accurate is it and does it have any problem with high altitude? I want to use it on a 3 stage rocket to measure the altitude and unattach the parts

I am using this with the Arduino and the sample code provided. When I first turn the on the Arduino and MPL3115A2, the device gives me a few valid data points then gives me nothing but -1 or 0xff. I have it set up to read Altitude. I used the Hookup Guide to connect it to the Arduino. Is this expected behavior? If not, does anyone have an idea as to what is going on?

.

Anyone got schematic on how to hook up this sensor and the RHT03 with a display? It would be great to make it portable. Thanks

Any suggestions on how to get this part into Fritzing?

The product page is missing the open hardware logo.

I have connected this device to an Arduino Uno Rev3. It works perfectly. But when I disconnect from the USB port of my mac and connect again it displays a wrong value, something like -170.xx

I have connected to I2C also a RTC DS1307, and they work perfectly after loading the sketch. The sketch is based on the linked Arduino example, with minor modifications: I have kept the functions for bcd conversion, setDate, getDate, toggelOneSHot, readPressure, I2Cread/write, setModeBarometer, setOverSampleRate (set to 128).

set setup is: // setup MPL3115A2 setModeBarometer(); // Measure pressure in Pascals from 20 to 110 kPa setOversampleRate(128); // Set Oversample to the recommended 128 if(IIC_Read(WHO_AM_I) == 196) display.println("MPL3115A2 online!"); else display.println("No response - check connections"); display.display(); //update display delay(3000); display.clearDisplay(); // delete old values }

Any idea why when reconnecting it does not work, but no message "No response - check connections" ? (BTW this message is correctly displayed if I disconnect either SLA or SDA pin).

Daniele

Amature question, but is there any way that I can change the analog inputs in the code from A4, A5 to A2, A3? If so how?

i have this module connected up to an arduino uno. 3.3VDC and using pins 4-5 and the example altimeter code. but i get incorrect readings for the pressure and altitude the temperature seems about right though.

this is the output Altitude(m):-25.25 Pressure(Pa):262043.00 Temp(c):23.75

my current altitude is approximately +40m is there are value i need to change or is my sensor faulty?

I am looking for a altitude sensor to use in a model rocket that will experience 90g of acceleration. Will this sensor function in high acceleration applications? If not is there a specific type of altimeter I should look for?

I just uploaded a library for this sensor for use with http://www.mbed.org devices. It was inspired by the Arduino example on this page. You can find it on the mBed website here.

I'm currently thinking about buying this sensor for a project. Does anyone know if this device needs any sort of calibration? If not, how does it manage to get such an accurate reading as stated in the product description?

Hi, my temperature is coming out right, but the altitude say -30 feet. Could I have a bad sensor?

Hi, I'm interested in using this sensor in a tracker device. I have a big doubt, this device would be used outdoors so it is going to be closed in a nylon case (waterproof). Would this sensor give accurate reading inside a case? I’m not sure if atmospheric pressure could be measured in this way. Thanks in advance

Is there anybody who hooked up this sensors together:

• MPL3115A2 Breakout (this one)
• HTU21D Breakout
• TSL2561 Breakout

All of them are 3.3V I2C, HTU21D and TSL2561 have an option to disable pull-up resistors, but looks like MPL3115A2 hasn't got this option. Can I use MPL3115A2 pull-up resistors and disable them on HTU21D and TSL2561? Will I fry something with this setup?

Pressure(Pa):-999.00 Temp(f):-1766.20 Pressure(Pa):-999.00 Temp(f):-1766.20 I keep getting this. I have Triple Checked every connection. I don't know how to fix this?

Has anyone tried using this sensor with a Digispark or another microcontroller that uses the ATtiny85 processor? I am struggling to get the source code to compile, I have tried changing the Wire.h references to TinyWireM.h but I have had no luck.

Is anyone able to help me out?

Thanks in advance!

The 1kohm pull-ups installed on this breakout are quite strong. I'm running this through the PCA9306 level translator which already has 1kohm pull-ups for the 3.3V lines and given there is an MPU-6050 on the same I2C bus the combined pull-up (1kohm + 1kohm + 10kohm parallel) seems to be too high for the MPU-6050 which refuses to work when this breakout is attached to the bus..

I'm guessing I could just go ahead and unsolder the pull-up resistors on this one to reduce the overall pull-up of the SDA/SCL lines?

Interestingly the HMC5883L has no resistors installed at all, instead relying on external pull-ups often provided by the master. The pull-up policy seems to be a bit chaotic when it comes to these breakouts. :)

Hi, I'm currently trying to run the the example codes on my Arduino Mega 2560 but the output in the Serial Monitor is constantly giving me the maximum negative value: "Pressure(Pa):-999.00 Temp(f):-1766.20", "Pressure(Pa):-999.00 Temp(f):-1766.20 Altimeter setting InHg:nan", or "Altitude(ft):-3277.56 Temp(f):-1766.20" when I am running the library codes, and "æfxxxàxæê&¿õËPäeËj1"... when I am using the Example Code. I have made sure to connect Vcc to 3.3V, Ground to Ground and SDA directly to A4 and SCL directly to A5. Any help would be much appreciated! Thank you.

Hi, From the datasheet: The Altitude data is arranged as 20-bit 2’s complement value in meters. The data is stored as meters with the 16 bits of OUT_P_MSB and OUT_P_CSB and with fractions of a meter stored in bits 7-4 of OUT_P_LSB. Be aware that the fractional bits are not signed, therefore, they are not represented in 2’s complement. Does somebody know how this is to be understood? Should I take the fractional part (LSB/256 units) and add it to the signed integral part? Or should I take the fractional part (LSB/256 units), multiply it by the sign of the integral part, then add the two? I don't have the part here so I cannot just try.. Thank you Regards Soren

Unlike other I2C devices, this device requires that the write operation before read will not be terminated with a stop command. Otherwise you will read only address 0....

I can't get the Arduino example to compile. It gets stuck at Wire.endTransmission(false);

 // Read pressure registers
 Wire.beginTransmission(MPL3115A2_ADDRESS);
 Wire.write(OUT_P_MSB);  // Address of data to get
 Wire.endTransmission(false); // Send data to I2C dev with option for a repeated start. THIS IS NECESSARY and not   supported before Arduino V1.0.1!
 Wire.requestFrom(MPL3115A2_ADDRESS, 3); // Request three bytes

The error messages are

MPL3115A2.ino: In function 'float readAltitude()':
MPL3115A2:140: error: no matching function for call to 'TwoWire::endTransmission(int)'
C:\Program Files (x86)\Arduino\libraries\Wire/Wire.h:52: note: candidates are: uint8_t TwoWire::endTransmission()
MPL3115A2.ino: In function 'float readPressure()':
MPL3115A2:192: error: no matching function for call to 'TwoWire::endTransmission(int)'
C:\Program Files (x86)\Arduino\libraries\Wire/Wire.h:52: note: candidates are: uint8_t TwoWire::endTransmission()
MPL3115A2.ino: In function 'float readTemp()':
MPL3115A2:238: error: no matching function for call to 'TwoWire::endTransmission(int)'

I'm using V1.0.5. Where am I going wrong?

Please advise what is the best male header pin that I should use to solder for breadboard use. Thanks

Does anyone know how much this product weighs? (preferably in grams)

Is it possible to assign a new i2c address to this device? I would like to have a few of these connected to the same arduino and didn't see these when I bought the BMP085.

What's Git all about? I work at home OFF LINE. NO BROADBAND. I have to PAY for wifi usage. Who needs that just to download an example.

Is it possible to read out both pressure and altitude? I need both values

Hi! I was wondering, is there a way to get data out of this sensor faster than 1Hz? I've programmed the example from page 12 of the datasheet (I chose interrupt driven acquisition). My sample rate seems to be limited by the ST bits in register CTRL_REG2 (0x27) because I can increase it by setting those differently, but I can't get it below 1 second. What do I need to change if I want to sample at the rate given by the over-sampling bits in CTRL_REG1 (0x26)? I can post my code here if you like. Your help is much appreciated :)

Hi! When establishing a handshake and reading from 0x0C I’m getting return in value 0, not 196. I would expect -1 or FF in case I2C is not established. I can not get any other data from the device. Only 0. Any suggestions?

For those out there using this device, I just learned from Freescale that the sensor die is sensitive to light. If you are having issues with accuracy or drifting measurements that don't correlate with the weather, light may be affecting the readings. The datasheet for this part does not say anything about this but the one for the MPL115A does mention it: "The sensor die is sensitive to light exposure. Direct light exposure through the port hole can lead to varied accuracy of pressure measurement. Avoid such exposure to the port during normal operation." I was very frustrated trying to use this sensor before I learned about this because the measurements seemed to be all over the place at times. Now I put a small piece of foam over the port to block out light but still allow the air to reach the sensor. I am now reliably getting +/- 1 foot accuracies which is totally amazing. Once you know how to use this part properly it is really awesome.

i am using Arduino DUE Board and the sketch available for due is not working.help me out....

Hi guys, this is my first post here so go easy on me!

I am building this circuit from scratch since my college didnt allow me to buy the breakout board so these are my problems:

1) I tried to design the circuit as in the schematic above and I was able to build it all even the MPL311 library (I had zero experience with Eagle before this lol)but I couldnt comprehend the arrow pointing at VCC so I made a circuit with all the physical connections. Now I keep getting inconsistency errors no matter how much I trouble shoot it. So is it the arrow? and if yes where can I find it?

2) I am using a DSPic30F for this project and unfortunately I cant find C example codes and I cant use C++, so is there by any chance a C-version of the Arduino example above?

Again, sorry for the inconvenience lads this is my first post.

Just got mine and wired it all up with an Arduino uno R3 and a 16x2 display, worked great with the example code above. One question I have is every time I have turned it on it is 10-20 meters higher than it was the last time, so I checked the local weather and the barometer has been steady, I kept testing but now I am getting my local altitude 400 higher than it actually is, not a big deal as I am using it in a zero'd out configuration but even then if I let it sit on the desk it slowly counts up, anyone have any ideas why this might be or how to re calibrate it? Thanks.

How does an altimeter based on pressure ever accurately report the altitude? Since pressure is changing minute to minute in the real world it seems like it would be constantly incorrect. Even if you went down to the beach at noon and calibrated it at sea level for 0ft of elevation, an hour later the weather changes a bit and your measurements are incorrect.

Unless I'm missing something, isn't the only way to accurately measure altitude via GPS (assuming at least 4 satellites)?

Atmospheric calculator at http://www.newbyte.co.il/

Is it possible to connect the I2C signal connections on the breakout board directly to the Arduino 5V logic pins? Or, is a logic level translation required?

Looks like its good to about 17,000 ft. based on the table at this site: http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

How low can this measure? Or what is the maximum altitude that can be accurately measured?