I did a test of this sensor relative to GPS altitude on a drive down highway 38 from Sugarloaf CA (near Big Bear) to Mentone, CA.. The results, as well as the Arduino code needed to reproduce my experiment is here:
http://sites.google.com/site/wayneholder/gps-vs-barometric-altitude
Wayne

Got this working on Arduino Pro Mini, here's the full code:
http://mitat.tuu.fi/?p=78

I used one of these sensors and 50 ft of 3/8" air compressor hose along with about $10 worth of other parts to make a secondary driveway vehicle sensor. When used with my IR sensor (already hooked up to a fio with an xbee attached), I can tell vehicle direction, i.e. ingress or egress. This sensor has a fast enough response that even a slight bump in pressure is detected at rates faster than 50ms intervals - plenty of time to detect a vehicle rolling over the hose. Really impressed with this sensor!

I'm running into some issues with my code and I hope someone could help. If I hard code the readings and calibration data that is shown on P.13 of the datasheet, I get the results shown in the datasheet, however, when I pull the real data and the real calibration off of the device, the pressure is way low (about 3.55psi, 24,500 Pa). The temperature readings are accurate, and when I change the oversampling, the results I get for pressure are consistent (about the same + expected noise) for oversampling of 0, 1, 2 and 3. I did have to play around with typecasting a bit to get things to match up with the reference code. I'd like to experiment with some other calibration data and readings to validate my calculations- at the moment, I have:

AC1=8515
AC2=-1156
AC3=-14476
AC4=34169
AC6=24839
B1=5498
B2=61
MB=-32768
MC=-11075
MD=2432

Oversampling (for this example) is 2

UT reads as 35405, which calculates to 21.5C

UP reads as 171740 (after the shift for oversampling), which results in a pressure of 24957, or 3.619psi. (way too low for my altitude, about 800ft ASL)

I'd appreciate if someone could either run my calibration an readings into their code and see if they get the same, or send me your calibration and readings I could run through my code.

FYI: this is being done in C on a PIC32 on a Digilent Uno32. I do plan to share the code once it works. I've got a bunch of things running on the same I2C bus under a scheduler I wrote- each sensor can have a different interval and it can do other operations on a different device while the I2C while the pressure sensor is waiting the requisite time.

I hope you don't start at trend putting pull-up resistors on I2C control lines. And if you do please pick the highest resistance (i.e. 10 kohm) as the vast majority of folks would be using a 100 kHz SCL clock rate.

i didn't read all the commets, but anyway i found out that in the library there is an error it's even easy to find out if you are going to decomment the line to print AC1 AC2 etc parameter, you will find out that is giving you unsigned results !!! instead, AC2 AC3 Mb Mc are signed ... and this is even enlighting because are too big numbers (in the examples AC2 is -934 and instead i got 64519 that is two's complemented !!!) please anyone knows how to fix it using this library? ore are you suggesting to write down the code from the biginning ? thanks

why the retirement?

hi , can someone tell me why they describe this sensor with an accuracy of 0.03 hPa ,but if you check the Bosch sensor datasheet is declared +/- 1.0 hPa ..... where is the truth ??

hi

Jim this code works great, Thanks!

I got this running on the FPGA of a National Instruments sbRIO 9606 embedded board.

https://decibel.ni.com/content/docs/DOC-23854

.

I think it's worth noting that this is not actually a barometric pressure sensor. It is simply a pressure sensor. It will report atmospheric pressure, which varies not only with the weather but with altitude. To convert this value to barometric pressure (which is atmospheric pressure adjusted for altitude) you must apply the formula in section 3.7 of the data sheet. If you apply that formula before you report your value, it should match up well with values reported by your local news station.

I'm having the same problem as hazmat - temperature reading is ok, pressure reading is too low (about 24 kPa).

my (bash) code: http://pastebin.com/H0XexiTY

output: ut=0x6e2a ut=28202 x1=6982.2070 x2=-2409.2948 b5=4572.9122 t=286.3070 temp=28.6307 ------------------------------------- up=0xacd3e0 up=11326432 up=353951.0000 b6=572.9122 x1=2.1520 x2=-297.6457 x3=-295.4937 b3=80293.0126 x1=-1019.2410 x2=440576.0942 x3=109889.7133 b4=148778.8297 b7=1710362421.2500 p=22992.0133 x1=8066.2851 x1=373.9223 x2=-2581.0583 p=23091.0048

Anyone know how fast the sensor can be read without getting repetitive data.In other words, how fast does it sample the air.

Hi I have a Picaxe 28x2 and want to use this barometric sensor (BMP085). The wireing is not a problem, but I cannot find the picaxe code for this. I all ready use a realtime clock on the I2C bus.

The code I use to read the clock is: readi2c 0,(seconds,mins,hour,day,date,month,year)

but what do i write to read the raw value from the barometric pressure?

Immense gratitude to the makers of the world who take the time to explore and share their findings. After 13 hours of searching/dissecting/migrating posted snippets of code, I discovered that NOT ONE functional demo of the BMP085 for Arduino 1.0+ exists. Dysfunctional findings include:

• the sparkfun tutorial @ http://www.sparkfun.com/tutorials/253
• http://mitat.tuu.fi/?p=78
• http://interactive-matter.eu/blog/2009/12/05/arduino-barometric-pressure-sensor-bmp085/
• http://bildr.org/2011/06/bmp085-arduino/

I was finally able to successfully debug the last article (@ bildr.org), mostly by fiddling with argument types. So if you replace the code in this otherwise awesome quickstart guide with this code ... http://ilabbali.com/code/Arduino_BMP085.cpp ... the BMP085 works great with Arduino 1.0+.

I tried posting the code here, but the sparkfun WYSIWYG parser totally mangles it.

After looking around, I found the code at http://mitat.tuu.fi/?p=78 ...; however, it's not compatible with Arduino 1.0.

I am starting to research what I need to change to make it compliant with the new IDE. Hopefully, it won't take much...

I am working on two BMP085 sensors. One of them is used to measure air pressure and the other is used as reference. I want to get the pressure offset value between these two sensors. I put them side by side to test the difference but everytime the offset is different. Anyone knows the reason? Thank you.

I got this a day or two ago and have it hooked up to the Arduino. I have tried just about everybody's code examples, and verified the calcs, but the pressure is about 1000 Pa too low. The temperature is correct, though. Suggestions??

if i want use two sensors,,how the skatch code?? i use arduino mega,,Thanks

I'm having some trouble with this sensor on my Uno & Maple. When I read the int for the temperature all I'm getting out is 0xFFFF - and I'm sure I'd notice if it was that hot! The calibration data seems to be coming out ok:

Reading Calibration Data AC1: 6574 AC2: -1087 AC3: -14387 AC4: 33903 AC5: 24939 AC6: 20628 B1: 5498 B2: 57 MB: -32768 MC: -11075 MD: 2432

So I don't think its a simple I2C error. Anyone got any ideas? Thanks.

I went ahead and did it and it works fine. I am concerned that I have different temperature readings from sensors side by side, but I'll calibrate.

Thanks

I now have both BMP085's connected and the XCLR working. But the values are off. I think I need to run the init before each one to get the calibration values.

Any harm in running // initialize BMP085 pressure sensor if (pressure_sensor.begin() == 0) error(1);

Just before reading them ? Thanks as always

Would this sensor stand up to mild acidic\base or solvent conditions do you think? I'm thinking of using it for a torr calculation that is exposed to such environments, only very very lightly, but I would like to know the longevity of such if somebody has used it as such.

Is it possible to use this sensor for both pressure and depressure?

I'm curious as to whether this sensor is capable of detecting the pressure changes in a 2U server case.

Let's say I have a full rack (23") 2U server going all the way back, let's then imagine that the internal compartments of the server are carefully sectioned off and have high flow 80mm fans for the primary induction stage (for HDD cooling), let's say we're using Delta's 80MM FFB0812EHE which according to it's datasheet can produce a pressure differential of 0.24" H20, let's say we have three of those in the primary stage which brings our positive pressure to 0.72" H20, if we convert that to in HG we get about 0.052959 which works out to 179.3 pascals.

However, if as the user pmatil asserts, the accuracy of the sensor is within 1hpa and not 0.03hpa (clarification please?) I'm in a conundrum about choosing it.

A 180 pascal pressure differential would probably be at the high end of what these fans could produce, and I'm interested in much more fine grained monitoring of the various subsystems airflow over time.

Could someone please differentiate accuracy from resolution as it pertains to this sensor?

Also, while I love the selection of sensors here at SF, I must note a relatively sparse selection of airflow sensors, there is only one anemometer and I'v seen much smaller handheld anemometers available for under $25, if all that is required is a free spinning magnetic rotor and a hall effect sensor, then such a sensor would be very valuable indeed for all sorts of applications.

The only other notable offering is from Modern Device and it uses a different technique which measures electrical resistance vs temperature in order to approximate a wind speed. I believe their product model number is: MD0545 (it's a breakout board) and the chip in question there is the TMP421.

Your time is appreciated

Thanks for the post below helix help me greatly as i was really struggling !

trying to get sensor to work for me - I've tried a number of the code bases posted here for the arduino and with all of them get stuck during the calibration step. specifically around this call (from Sparkfun's code):

ac1 = bmp085ReadInt(0xAA);

as I debug this method it seems to hang in the function bmp085ReadInt() method:

Serial.println("bmp085ReadInt - 1"); Wire.beginTransmission(BMP085_ADDRESS); Serial.println("bmp085ReadInt - 2"); Wire.send(address); Serial.println("bmp085ReadInt - 3");

"bmp085ReadInt - 3" never shows up in the serial output window.

any suggestions? i ordered a couple of more just in case I have a bad one here

Be a bit patient, new to some of the technologies here.

How do I address a second BMP085 sensor ?

I'm deploying a sparkfun weather station as part of a water quality initiative. I've modified the code to work for what we need, but I need to add two more sensors to the package. The one that is causing me the most concern is water depth. The tide drives change in the water level.

I'm planning on using a BMP085 inside a collapsible bladder at the bottom of the lagoon, and then measuring the pressure inside the bag as the water level moves up and down. Depth varies from 1 ft to 4 ft.

The board has one BMP085 on it already for the air pressure. So I am adding a second. I can't quite figure out how to address the second sensor !

Any suggestions welcome. Not my most experienced area.

FYI, I was just playing around with the Android SensorManager on my Motorola Xoom tablet and found out that it has the BMP085 on board.

I've been running my BMP085 off the +5 volt rail inadvertently for over a month. I'm not proud of the fact that I can't read a data sheet. But, I will say that it has been working. I did have a strange anomaly come up last night on my weather station, where the BMP085 lives. When the pressure was rising and the temperature was falling, all of a sudden the pressure jumped about 350 Pa and then as the temperature came back up and the pressure fell, the jump reversed itself. Odd. I'm going to implement Member #236519's suggestion. Go see KWIAPPLE11 on Weather Underground. That's me.

FYI: I put together cpp library, please see: http://code.google.com/p/bmp085

#include "bmp085.h"

bmp085 BMP085;

void setup()
{
  Serial.begin(9600);
  BMP085.Calibrate(); 
}

void loop()
{
    BMP085.refresh();
    Serial.print(BMP085.pressure);
    Serial.print(", ");
    Serial.println(BMP085.temperature);

    delay(5000);
}

Hi, would it be possible to make this sensor a wireless device? Does anyone know a good resource to show me how that would be accomplished? Thanks, Tom

I had my sensor running fine logging to pachube with the ethernet shield then it started logging 0 for both pressure and temperature, I have tried connecting xclr to GND to attempt a reset but no change. Is my sensor broken??

These sensors are pretty good... up to around 37km altitude.
Then they start reporting some weird data :-)
We took one up to 40.575km on our Horus 15.5 high altitude balloon flight, it reported pressure down to 2hPa before outputting gibberish data. It recovered again on the way back down.
Still, pretty damn good for a sensor only rated down to 300hPa :-)

This may be obvious to some but the instructions just blindly say use pins A4 and A5 but on the Ardunio mega 2560 you have to use pins 20 (SDA) and 21 (SCL).

Can I use it as an altimeter? I need to open a parachute before my package crashes into the ground (need to interface it to an Arduino board)

I just purchased this sensor from a local shop. It works. Though I spent a good amount of time looking at the issue of having a 3.3 v device on a 5 v I2C bus before I connected this little sensor to my Arduino Uno. I was prepared to construct a level shifter, until it occurred to me that it might be possible to disable the internal Atmel 328 pull up resistors for the I2C bus.
It is possible to do this by changing the wire library. Here's the link: http://www.varesano.net/blog/fabio/how-disable-internal-arduino-atmega-pullups-sda-and-scl-i2c-bus Now all I do is pull the SDA and SCL lines to 3.3 v, which this sensor does. And my other 5V device (DS1307) is perfectly happy with the 3.3v bus voltage. Thanks to Sparkfun for this product!

We bought BMP085 from Sparkfun and used C8051F340 to communicate with it via I2C.
Temperature measured 23.1 degC.
The pressure measured was 99568 Pa. The local weather station had 29.47 in = 99 785 Pa
These are the dig. signals over the i2c bus.
AC[12345] = {10377, -1393, -14300, 35532, 24474, 20309}
B[12] = {5498, 78}
M[BCD] = {-32768, -11075, 2432}
UP = 368764, UT = 28522.
I would say the complexity level of this device is more than I expected.
Overall this device is working great.

(1) Has anyone got code to read the BMP085 with a Basic Stamp
or PICaxe ?
(2) I'm interested only in pressure variations, not absolute
value. I wonder if I can omit some of the calibration steps ?

Hopefully somebody knows the answer to the following mystery or could give me some hints to solve it: I'm using two barometer sensors: the BMP085 (I2C) and the SCP1000 (SPI). Somehow the values of both sensor are way off.
First the temperature:
The SCP1000 tells me it's 25.15C while the BMP085 thinks it is 28.1C while in fact it is much cooler around 21C.
Then the pressure:
SCP1000: 101767Pa
BMP085: 103962Pa
The SCP1000 seems to be closest to the actual value. Both sensor are located on the same board.
Suggestions are welcome!

Can this be used with Adafruit's data logging shield, which also uses i2c on analog pins 4 and 5? The pins are open and solderable.

does anyone knows if the temperature measurement works with negative values ? lets say down to -20degC ?

[delete this comment]

Are you sure this part is in the Eagle library? I think the latest (at time of writing, the April 13th 2010 version) has the sensor itself, but not the breakout board.
Anyways not too hard to make yourself, but yeah, not in the library (yet)

I agonized over designing a product around this chip or the much more expensive SCP1000. The SCP1000 claims to be accurate to within a 9cm column of air (raise/lower it 9cm for a different altitude reading). I had to do the math on the BMP085 because all they give is an accuracy of 0.03 hPa, that works out to 9.75 inches or 25 cm at sea level, about three times that of the SCP1000 but still fantastically accurate for an altitude based product. If you want to see the math 0.03hPa = 3Pa, and at sea level a foot change equals 3.7Pa

This works, but not with my 28j60 ethernet shield, which uses SPI as well. I see someone connected theirs to analog 4 and 5, not like the example showing SDA and SCL to digital 0 and 1?
Firing this up locks up the etnernet shield.

sunrise@sunsys.net: _I'm not getting the pressure accuracy ... local weather stations report 30.16 inHg (1013.25 millibar) but the sensor is reporting 99500 (995.00 millibars). _<br />
<br />
Okay, weather reports provide pressure corrected to sea level so that comparisons between stations can be made. The sensor reports current pressure only.<br />
<br />
Altitude relative to sea level can be calculated using the sensor's pressure value like this:<br />
<br />
altimeter_setting = (float)101325*pow(((288-0.0065*known_altitude)/288),5.256);<br />
<br />
altitude_meters = 44330 * (1.0 - pow((float)pressure/((101325+pressure)-altimeter_setting),(1/5.255)));<br />
<br />
<br />
But that's not the whole story, I think my sensor is still providing an odd value. Using actual data from the sensor (my altitude is 206 metres ASL):<br />
Pressure from sensor(Pa): 97880<br />
altimeter_setting calculated: 98873<br />
altitude_meters: 208<br />
<br />
Weather Underground reports 100500 Pa at my location.<br />
<br />
<br />
Thank you to http://www.experts123.com/q/is-the-reported-barometric-pressure-adjusted-to-sea-level.html. I looked at lots of other sources but this had the best explanation, and a formula for sea level correction that seems to work!<br />
<br />
<br />
<br />

this is very accurate as the value keeps the same with the local weather station nearby!

Fabulous sensor -- just got it working on my bench after not playing with it for months.
A lot more computationally intensive than http://www.sparkfun.com/commerce/product_info.php?products_id=8161

I am using the BMP085 with the new Arduino Uno and a Logic Level Converter (http://www.sparkfun.com/commerce/product_info.php?products_id=8745). Whenever I call Wire.endTransmission() I get error code 2 (received NACK on transmit of address). All the boards are un-modified and I have to following connections:
A - Arduino
L - Logic Level Converter
B - BMP085

Power

A,3.3V L,LV
A,3.3V B,VCC
A,5V L,HV
A,GND L,GND
A,GND L,GND
A,GND B,GND

Data

A,Digital4 L,Ch1,TXO
A,Digital5 L,Ch2,TXO
B,SDA L,Ch1,TXI
B,SCL L,Ch2,TXI
Voltages seemed fine (3.28V on 3.3V rails). Any thoughts? Could I have burned it out when I soldered on the headers (It was hot to the touch after 5-10 seconds)? And lastly, how would I test the chip with only an Arduino and multimeter? I am new to the electronics part of this.

I've just got this to work with the Bus Pirate. Great sensor. One note though about the product description... The absolute accuracy is +/- 1 hPa, not 0.03 hPa. Resolution is down to 0.03 hPa.
Converting the coefficients was the hardest job since the datasheet nor the application note give the conversion formula. It's only in C-code. And since I'm not that good at C it took a little time to understand how some of the coeffs are negative.
If you are deciding between this and MPL115A2I2C take this. I have both and MPL115A's coeffs are way harder to convert (fixed point numbers).

I tried the suggested code and the change in line 58 to "long ut= bmp085_read_ut();", but results are still strange. I got 272 for the temperature, and 99615
for pressure (that could be true, but I'm not sure). Can anyone with working code post a link. Would be much appreciated. Thanks!

@ scoopjones, use this example code, http://mitat.tuu.fi/?p=78, from Finnishguy. It works perfect, I've been meaning to turn it into a library just haven't gotten around to it yet, I'll post something when I do, hope it helps

Does anyone have Arduino code for this that works? I've tried several versions from different spots on the Internet and always get unusable results. As far as I can tell, the problem is that the Arduino doesn't have a "short" variable type (-127 to 127), which is required for reading the registers. I may be wrong, but I'm definitely spinning my wheels. Thanks!

I've followed the spec sheet powering it at 3.3V and haven't had a problem, it's worked perfect and readings are comparable if not the same as the local weather.

No Joy. I noticed that the digital power pin isn't connected and if I put a CRO on it I notice that the voltage on the digital power pin is decaying to zero volts when I attempt to communicate to it.
The XCLR pin which is internally connected to the digital power pin is following the same pattern.
The sparkfun wiring example indicates that the device should be powered by 5volts. This is in excess of the absolte max in the Bosch data sheet (4.25V).
What has everyone else been using to power this device?
Are there any breakout boards available with pin 4 (digital power pin) connected?

I desoldered the sensor from this board and found that pin 4 (Vddd) is not connected. The schematic indicates that it should be routed to Vcc. The board still works reasonably well so presumably the digital part of the chip is deriving power through some unintentional path such as the analog supply or the i2c pins.

All i can say is finally! I've been waiting for this for months ever since I suggested it back in January. Can't wait till you have it back in stock.