[Paparazzi-devel] battery voltage for rotorcrafts, changes for booz board users

[Felix Ruess]

Hi all,

since Antoine recently added support for the electrical subsystem for
rotorcrafts (replacing battery) we now have the same code there as for
fixedwings.
Hence we now also have battery voltage measurement for Lisa/L.

For users of the booz board this means that you might have to set the
conversion factor from ADC measurements to Volts in your airframe
file.
This is set now with the VoltageOfAdc(adc) macro just as for
fixedwings, the formerly used BATTERY_SENS and BATTERY_OFFSET are not
used anymore.

So far you probably had something like this in your airframe file:
<section name="BAT">
  <define name="BATTERY_SENS" value="0.246" integer="16" />
</section>
You need to change this to
<section name="BAT">
  <define name="VoltageOfAdc(adc)" value ="(0.0246*adc)"/>
</section>

The default value VoltageOfAdc(adc) for the booz board is
(0.0183*adc), which should be correct if you have a recent revision
with R1=4,7kOhm and R2=1kOhm.
Depending on the revision of the booz board you have (mine is the
first revision like in the example above), you might have different
values for the two resistors making up the voltage divider.

This factor can be computed like this:
     reference_voltage / adc_max_value * (R1 + R2)/R2
R1 and R2 make up the voltage divider to measure Vbat.
So for the current booz board revision we have
     3.3/1023 * 5.7/1 = 0.018387097

Cheers, Felix