Re: [Paparazzi-devel] airspeed_adc with Ardupilot airspeed sensor

[Hector Garcia de Marina]

On Mon, Jul 2, 2012 at 5:18 PM, Tilman Baumann <address@hidden> wrote:

On 02/07/12 15:56, Gareth Roberts wrote:

Hi Tilman,

It's the same sensor as the ardupilot classic - it's not great.

but cheap. :D

>From http://code.google.com/p/ardupilot/source/browse/ArduPilot_2_8/sensors.pde

// in M/S * 100
void read_airspeed(void)
{
       #if GCS_PROTOCOL != 3
       airpressure_raw = ((float)analogRead(AIRSPEED_PIN) * .10) + (airpressure_raw * .90);
       airpressure     = (int)airpressure_raw - airpressure_offset;
       airpressure     = max(airpressure, 0);

I suppose up until here it's all filtering?

Yes,

airpressure_raw = ((float)analogRead(AIRSPEED_PIN) * .10) + (airpressure_raw * .90);

is a first order low pass filter. You must be careful here, as the coefficients are hard coded, if you change the

sample time, the cut frequency changes. You should put this coefficients as functions of the sample time.

Take a look at wikipedia (Discrete time realization): http://en.wikipedia.org/wiki/Low-pass_filter

Héctor