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AP_IOMCU: dither heater pin to prevent 1Hz impact on mags 

with the simpler duty cycle code we see a 1Hz 25 mGauss cycle in the
internal mags
This commit is contained in:
Andrew Tridgell 2019-07-12 09:42:21 +10:00
parent 77f8ec9f43
commit 76a8d494c3
1 changed files with 6 additions and 3 deletions
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9
libraries/AP_IOMCU/iofirmware/iofirmware.cpp
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@ -295,9 +295,12 @@ void AP_IOMCU_FW::heater_update()
// turn off the heater
HEATER_SET(!heater_pwm_polarity);
} else {
uint8_t cycle = ((now / 10UL) % 100U);
//Turn off heater when cycle is greater than specified duty cycle
HEATER_SET((cycle >= reg_setup.heater_duty_cycle) ? !heater_pwm_polarity : heater_pwm_polarity);
// we use a pseudo random sequence to dither the cycling as
// the heater has a significant effect on the internal
// magnetometers. The random generator dithers this so we don't get a 1Hz cycly in the magnetometer.
// The impact on the mags is about 25 mGauss.
bool heater_on = (get_random16() < uint32_t(reg_setup.heater_duty_cycle) * 0xFFFFU / 100U);
HEATER_SET(heater_on? heater_pwm_polarity : !heater_pwm_polarity);
}
}