easymotor-v3: Fix pressure to adc conversion to use reference voltage

Wasn't taking reference voltage into account, which meant the computed values
were 3.3 times too high.

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/src/easymotor-v3/ao_pins.h b/src/easymotor-v3/ao_pins.h
index 5cc95eb93b0eb0da5b1ff0edc6efee355673bac0..b3be803e40cda84373735046ae2dc1a627ae345c 100644 (file)
--- a/src/easymotor-v3/ao_pins.h
+++ b/src/easymotor-v3/ao_pins.h
@@ -167,14 +167,20 @@ static inline int16_t ao_delta_pressure_to_adc(uint32_t pressure)
        static const double volts_base = 0.5;
        static const double volts_max = 4.5;
 
+       /* Compute change in voltage from the sensor */
        double  volts = (double) pressure / AO_FULL_SCALE_PRESSURE * (volts_max - volts_base);
-       double  adc_volts = volts * 10.0/15.6;  /* voltage divider in front of the ADC input */
-       if (adc_volts > 1.0)
-               adc_volts = 1.0;
-       double  adc = adc_volts * 32767.0;
 
+       /* voltage divider in front of the ADC input to decivolts */
+       double  adc_dv = volts * 10 * 10.0/15.6;
+
+       /* convert to ADC output value */
+       double  adc = adc_dv * AO_ADC_MAX / AO_ADC_REFERENCE_DV;
+
+       if (adc > AO_ADC_MAX)
+               adc = AO_ADC_MAX;
        if (adc < 0)
                adc = 0;
+
        return (int16_t) adc;
 }