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February 2, 2009
about 2 years ago
These are great wireless modules. For an alternate Arduino library and development platform, see the JeeLabs website. My ColorNode board can also be used as a simple breakout board for this module and is based off of the JeeNode. The design is shared on OSHPark.
about 2 years ago
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.
In converse, if you want to use this sensor as a barometric pressure sensor and have its reading correspond to those of local weather reports, the sensor readings must be scaled based on your local elevation. I found the equation here to be useful. In software I defined the local ELEVATION (in feet) and then used the following formula:
elevation_offset = 101325-101325*pow((1-0.0000225577*ELEVATION*0.3048), 5.25588);
When you read out the pressure value from the sensor, add the elevation_offset and divide by 100 (mBar) or 3386 (inHg) - you should arrive at about the same value as local weather stations.
The calibrated range is 50 to 110kPa but the specs say it is operational down to 20 kPa. That would mean it would work to about 35,000 feet or so. However, I imagine the accuracy is not as good at the extent of the measurement range. For those who might be interested, I am using this part with good success on a miniature rocket altimeter which I call AltStick.
about 3 years ago
Suggestions for SparkFun for this and other GPS boards:
Use a thinner board material (0.031" versus 0.062"). This would allow you to use a more manageable width for your 50ohm RF microstrip.
The GeoHelix antenna is amazing and it would be cool if the board could be made such that either that antenna or an SMA connector could be attached. They both use a similar footprint and can be made interchangeable.
Otherwise, this board looks really great. Do we know if special firmware is necessary for the unit to be used at high altitudes?
I have used the suggested capacitor before as a VBAT backup for a different GPS module (Inventeksys ISM300F2-C5.1-V0004) and it works well. If you plug in the numbers (3.3V, 0.2F, 200ohm internal resistance, 9mA charge) into this website and take the results as charge time instead of discharge time, it says it would fully charge in 20 seconds. If you run it the other way, with 10uA discharge down to 1.5V, it does say the cap should provide greater than 7 hours of backup time. You can see some pictures of PCBs I created with that capacitor and the Inventeksys module here. I had originally used a coin cell but this capacitor is smaller, lighter, and just worked better.
about 5 years ago
BOC! BOC! w00T!
about 5 years ago
Can you provide a 3D model for this case? I want to use this for a project I am modelling everything up first to make sure drill holes and components (PCB, LCD, connectors, etc.) fit and line up properly. IGES, STEP, SolidWorks, or Pro-E would be great. Thanks!
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