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Simplify and improve the writeMicroseconds() calculations #66

Merged
merged 3 commits into from
Nov 3, 2019
Merged

Simplify and improve the writeMicroseconds() calculations #66

merged 3 commits into from
Nov 3, 2019

Commits on Oct 29, 2019

  1. Simplify and improve the writeMicroseconds() calculations 

    Checked the calculations by hand

Use Datasheet 7.3.5 Equation 1 for frequency from prescale
https://cdn-shop.adafruit.com/datasheets/PCA9685.pdf
Frequency = (ClockFrequency/(PreScale+1))*(1/BitRate)
and from the rest of the calculation
us per period = PulseLength/Frequency
us per bit = us per period/BitRate
 we can combine to get
us per bit = (PulseLength/((ClockFrequency/(PreScale+1))*(1/BitRate)))*(1/BitRate)

This can be simplified to (PulseLength (PreScale + 1))/ClockFrequency 
this formula was implemented in proposed code

checked by setting chip frequency to 60Hz
read prescale = 105
us per bit = 4.069 with 25Mhz (a PWM frequency of about 57.3hz)
Choosing the FREQUENCY_CALIBRATED constant listed at 104.3% higher or 26.075MHz
we get 
us per bit = 4.1035 or a PWM frequency of about 60.056Hz much closer to the set 60Hz 

Overall this change makes less calculation steps, and uses fewer variables. The change should be faster and more accurate to the intended results.
    @photodude
    photodude committed Oct 29, 2019
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  2. Wrap print statement in #ifdef ENABLE_DEBUG_OUTPUT 

    debug statements should be Wrapped in `#ifdef ENABLE_DEBUG_OUTPUT`
    @photodude
    photodude committed Oct 29, 2019
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  3. Change prescale from double to uint16_t 

    Prescale values are integers 3 to 255 with a maximum of 255+1 for the calculations.
    @photodude
    photodude committed Oct 29, 2019
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