Example: Using ADC configuration file to compensate sensor offset

The Air Data Computer Asgard can be controlled using the specific command set documented here on the repo.

Sometimes it is necessary to compensate the sensors readings for an offset. Let’s pretend we want to compensate for the offset of the differential pressure sensor. That can be accomplished by sending the command

$CCS,EXE,1,1

through the ADCs USB or the Bluetooth interface. It will be necessary to recalibrate the unit each time the ADC is power up. That can be quickly done using a free scriptable serial terminal.

Alternatively, it may be convenient to use a configuration file stored in the microSD card.

The configuration file can be used to set many other useful parameters like the string to be transmitted, the default log file name, the data frequencies at boot time and so on.

In fact, as soon as the ADC is powered on, the firmware will check whether the config file is present. If the file exists, the ADC firmware executes all the commands written into the file, one by one sequentially.

The ADC’s configuration file must be named “CONFIG.CFG” and must be placed in the microSD root path.

So to automatically set the offset at power on we will use a config file with only a line like:

$CCS,EXE,1,1

It should not be appropriate to zero the differential pressure in windy conditions, think of a pitot mounted on a plane. So it can be more practical to calibrate the sensors offset indoor.

In this case, we will follow these steps.

  1. Send the following command to ADC: 
    $CCS,EXE,1,1
  2. In few seconds the ADC will reply. For example, if the ADC answers 
    $CCA,1,45

    you have to note the offset value 45

  3. Place a “CONFIG.CFG” file in the microSD root; the file will contain the line 
    $CCS,USE,1,1,45,,

    where 45 is the offset precedently noted.

The command stored within the config file instructs the unit to use an offset value of 45 for the differential sensor readings. This latest solution relies on the low time drift of the sensor calibration.  It is necessary to repeat the operation regularly. For most uses, an offset annual calibration should be proper. Each one of the three shown procedures fits well for specific applications, in the end, the user will decide what is the most comfortable.