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

[Tilman Baumann]

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?
> airspeed                = sqrt((float)airpressure / AIRSPEED_RATIO) * 
> 100;

Have to put my thinking cap on for a while. Calculation looks similar 
enough that I could turn that into ppz style
  float airspeed = (adc_airspeed_val - AIRSPEED_BIAS);
  airspeed = sqrtf(airspeed) * AIRSPEED_QUADRATIC_SCALE;


> #endif
>
>
>         airspeed_error = airspeed_cruise - airspeed;
> }
>
> #define AIRSPEED_RATIO 0.1254   // If your airspeed is 
> under-reporting, increase this value to something like .2
>
> Cheers,
> Gareth