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Re: [Paparazzi-devel] airspeed sensor

From: Tilman Baumann
Subject: Re: [Paparazzi-devel] airspeed sensor
Date: Wed, 19 Dec 2012 11:16:09 +0000
User-agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/17.0 Thunderbird/17.0

On 19/12/12 10:33, Árni Þorvaldsson wrote:
Hi all,
I have an Airspeed Kit with MPXV7002DP that is available at DIY drones 
( and I was 
wondering if there are any modules ready for that sensor?
Sure. You can use airspeed_adc. You just have to come up with the right values for AIRSPEED_SCALE AIRSPEED_QUADRATIC_SCALE AIRSPEED_BIAS Those values don't correspond directly to what is done in Ardupiolot. But with some twisting in your mind, I'm sure you will get the right values converted. (I did it a while ago. If you search through the ml history. But I never flew those values)

The real bugger is, that this sensor has a voltage range of 5V. Which was unusable for me since the stm32 processor has only 3.3V ADC. Also, zero differential pressure is set at somewhere around 2.5V. You never have negative airspeed, so half of the measurement range (and resolution) is lost. Also, I did some bench tests and found the signal a bit noisy. But I'm not a expert in that. Perhaps the filtering that is done in paparazzi is not adequate. Ardupilot seems to filter much more heavily. I suggest you go and search for the original mailing thread., as I don't remember all details. I never concluded that, I just went with the ready build and calibrated Eagletree Airspeed sensor. Which is much much more expensive, but except for some unrelated i2c inadequacies never caused me grief.


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