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Re: [Paparazzi-devel] Cannon Launch Detection

From: Pascal Brisset
Subject: Re: [Paparazzi-devel] Cannon Launch Detection
Date: Mon, 04 May 2009 21:45:53 +0200
User-agent: Thunderbird (X11/20090409)

Hi David,

the modules mechanism should (almost) provide the features you require. You will have to write: - a module description, a file in conf/modules/ : In your case, it will contain only a call to your init function, a call to your periodic task and the declaration of .c and .h files:

<!DOCTYPE module SYSTEM "module.dtd">
<module name="cld">
   <file name="cld.h"/>
 <init fun="cld_init()"/>
 <periodic fun="cld_check()" period="1./60" autorun="TRUE"/>
   <file name="cld.c"/>
   <flag name="ADC_CLD" "ADC_7"/>

- your .c and .h files in the sw/airborne/modules/cld/ folder:

---8<--- .h ---------
#include "std.h"
bool cld_launch_detected;

---8<--- .c ---------
#include "cld.h"
void cld_init(void) {
 ... initialisation code for your adc ...
 cld_launch_detected = false;
void cld_check(void) {
 if (... check condition...) {
    cld_launch_detected = false;
    cld_cld_status = MODULES_STOP; // stop calling me

- your flight plan, for example using an exception in the Holding Point block (in basic.xml):

   <block name="Holding point">
     <exception cond="cld_launch_detected"  deroute="Takeoff"/>

- and finally in your airframe file:

   <load name="cld.xml"/>
# in the makefile section:

In the current implementation, 60Hz is the maximum frequency for a periodic task in a module. If you really need more ... let us know :-)

Hope this is enough

And feel free to update the wiki :-)


David Bryant wrote:

I'm attempting to extend paparazzi to detect rapid acceleration launch from a cannon. The cannon is activated by a separate system. The aircraft is accelerated at approximately 24 g-force along a 3 metre barrel length.

I need to detect the launch within paparazzi immediately and am investigating an approach based on sampling the output from a ADXL321 accelerometer on an ADC paparazzi input.

I was hoping to be able to create a function that was periodically invoked at say 200Hz and polled the accelerometer ADC input. The routine would process the data until some criteria had been met that indicated a launch. On detecting a launch the routine would do something (invoke a function?) that would allow cause flightplan to progress to the next stage. After this the routine would no longer need to be called.

I am currently going down the path of using the conf/modules mechanism to define my function and its periodicity, and writing the function.

Could someone please provide some general advice and any tips in regard to my approach or an alternative approach? I am having trouble finding any precedence or examples of this kind of thing. Can you draw my attention to a example that I should be looking at?


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