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

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 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

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.

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.

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’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.

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!

@ 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

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!

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 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.

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

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

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).

Okay, weather reports provide pressure corrected to sea level so that comparisons between stations can be made. The sensor reports current pressure only.

Altitude relative to sea level can be calculated using the sensor’s pressure value like this:

altimeter_setting = (float)101325pow(((288-0.0065known_altitude)/288),5.256);

altitude_meters = 44330 * (1.0 – pow((float)pressure/((101325+pressure)-altimeter_setting),(1/5.255)));

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):

Pressure from sensor(Pa): 97880

altimeter_setting calculated: 98873

altitude_meters: 208

Weather Underground reports 100500 Pa at my location.

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!

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.

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

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)

[delete this comment]

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

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.

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!

(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 ?

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.

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!

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)

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).

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 :–)

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??

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

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);
}

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.

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.

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.

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.

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