sunrise@sunsys.net

Member Since: November 4, 2009

Country: United States

  • Product DEV-09950 | about 3 years ago

    I followed Moggie100’s link to the Flightsim.com USB HID implementation - which is based on http://www.cesko.host.sk/ firmware. Interesting, but too much time & effort for me to adapt to Arduino … if the Arduino is even capable of it.
    I came across a product called U-HID - unfortunately not Arduino-based - if all you need is a configurable USB HID device http://www.u-hid.com/home/uhid_nano.php. Looks like a good candidate for custom game controllers, or in my case to adapt an old CH FlightSim Yoke from 15-pin to USB.

  • Product SEN-09694 | about 3 years ago

    I have received information from a Bosch engineer, who points out that:
    - a pressure vessel would be needed to determine the accuracy of the sensor … local weather stations may be too far away, or their reports to old, to use as a reference
    - the calibration of the altimeter I was using is unknown
    - the sensor is very accurate but not an “ideal” sensor
    - the specification document mentions a possible offset (“up to 1 hPa”) as a result of soldering techniques, which would not be included in the on-chip calibration data stored in EEPROM

  • Product SEN-09694 | about 3 years ago

    Today I obtained values from an aircraft altimeter … set to 0 feet it reads 29.34 (993.566 hPa); set to 700 feet it reads 30.05 (1017.61 hPa). The latter agrees with Weather Underground (1017 hPa and rising).<br />
    <br />
    The BMP-085 sensor output (after the equations in the datasheet) is 988.10, and corrected to sea level 1012.75. So it seems like the sensor output is 5.466 hPa too low, and as a result the sea level correction is 4.86 too low also.<br />
    <br />
    Re-checking my program, I manually substitute the pressure reading from the 0 feet altimeter 993.56 and the sea level corrected output is 1018.08 - which is much closer to the 700 feet altimeter reading, the error is only 0.45 hPa.<br />
    <br />
    Re-checking the program calculations from the datasheet, using the datasheet calibration values and input pressure, the output pressure is the same as given in the datasheet example.<br />
    <br />
    So my conclusion is the sensor is reading too low -about 5.4 hPa.

  • Product SEN-09694 | about 3 years ago

    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)101325pow(((288-0.0065known_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 />

  • Product SEN-09694 | about 3 years ago

    I don’t know if this is related, but I found this post http://www.picbasic.co.uk/forum/showthread.php?t=13081 that mentions the sensors are affected by light.<br />
    <br />
    Indeed, I shone a flashlight onto the sensor and the readings went from 99826 to 99710, which affected my altitude calculation - it went from 208m to 227m.<br />
    <br />
    Perhaps some of the other comments on the post are relevant also (stressing of the substrate)?

  • Product SEN-09694 | about 3 years ago

    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 />
    Temperature 22.5 C looks right.<br />
    <br />
    For the altitude calculation below, I need to subtract about 650 from the pressure reading, making it 99500-650=98850, in order to come out at the correct local altitude.<br />
    <br />
    <br />
    altitude = 44330 * (1.0 - pow((float)pressure/101325.0,(1/5.255)));

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