Re: [Paparazzi-devel] airspeed sensor

[Tilman Baumann]

On 19/12/12 10:33, Árni Þorvaldsson wrote:
> Hi all,
> I have an Airspeed Kit with MPXV7002DP that is available at DIY drones 
> (http://store.diydrones.com/Kit_MPXV7002DP_p/kt-mpxv7002dp-01.htm) 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.

Cheers
  Tilman