Copied version 1.37m from mikrocontroller.net svn

Author: Markus Seidl

ADC.c

@@ -0,0 +1,191 @@
+/* ************************************************************************
+ *
+ *   ADC functions
+ *
+ *   (c) 2012-2017 by Markus Reschke
+ *   based on code from Markus Frejek and Karl-Heinz Kübbeler
+ *
+ * ************************************************************************ */
+
+
+/*
+ *  local constants
+ */
+
+/* source management */
+#define ADC_C
+
+
+/*
+ *  include header files
+ */
+
+/* local includes */
+#include "config.h"           /* global configuration */
+#include "common.h"           /* common header file */
+#include "variables.h"        /* global variables */
+#include "functions.h"        /* external functions */
+
+
+/* ************************************************************************
+ *   ADC
+ * ************************************************************************ */
+
+
+/*
+ *  read ADC and return voltage in mV
+ *  - use Vcc as reference by default
+ *  - switch to bandgap reference for low voltages (< 1.0V) to improve
+ *    ADC resolution
+ *  - with a 125kHz ADC clock a single conversion needs about 0.1ms
+ *    with 25 samples we end up with about 2.6ms
+ *
+ *  requires:
+ *  - Probe: input channel of ADC MUX (lower 4 or 5 bits)
+ *           must not include setting of voltage reference
+ *
+ */
+
+uint16_t ReadU(uint8_t Probe)
+{
+  uint16_t          U;             /* return value (mV) */
+  uint8_t           Counter;       /* loop counter */
+  uint8_t           Bits;          /* reference bits */
+  uint32_t          Value;         /* ADC value */
+
+  Probe |= ADC_REF_VCC;            /* use AVcc as default reference */
+                                   /* and external buffer cap anyway */
+
+sample:
+
+  ADMUX = Probe;                   /* set input channel and U reference */
+
+  /* 
+   *  dummy conversion
+   *  - if voltage reference has changed run a dummy conversion
+   *  - recommended by datasheet
+   */
+
+  Bits = Probe & ADC_REF_MASK;     /* get reference bits */
+  if (Bits != Cfg.RefFlag)         /* reference has changed */
+  {
+    wait100us();                   /* time for voltage stabilization */
+
+    ADCSRA |= (1 << ADSC);         /* start conversion */
+    while (ADCSRA & (1 << ADSC));  /* wait until conversion is done */
+
+    Cfg.RefFlag = Bits;            /* update bits */
+  }
+
+
+  /*
+   *  sample ADC readings
+   */
+
+  Value = 0UL;                     /* reset sampling variable */
+  Counter = 0;                     /* reset counter */
+
+  while (Counter < Cfg.Samples)    /* take samples */
+  {
+    ADCSRA |= (1 << ADSC);         /* start conversion */
+    while (ADCSRA & (1 << ADSC));  /* wait until conversion is done */
+
+    Value += ADCW;                 /* add ADC reading */
+
+    /* auto-switch voltage reference for low readings */
+    if (Counter == 4)                   /* 5 samples */
+    {
+      if ((uint16_t)Value < 1024)       /* < 1V (5V / 5 samples) */
+      {
+        if (Bits != ADC_REF_BANDGAP)    /* bandgap ref not selected */
+        {
+          if (Cfg.AutoScale == 1)       /* autoscaling enabled */
+          {
+            Probe &= ~ADC_REF_MASK;     /* clear reference bits */
+            Probe |= ADC_REF_BANDGAP;   /* select bandgap reference */
+
+            goto sample;                /* re-run sampling */
+          }
+        }
+      }
+    }
+
+    Counter++;                     /* one less to do */
+  }
+
+
+  /*
+   *  convert ADC reading to voltage
+   *  - single sample: U = ADC reading * U_ref / 1024
+   */
+
+  /* get voltage of reference used */
+  if (Bits == ADC_REF_BANDGAP)     /* bandgap reference */
+  {
+    U = Cfg.Bandgap;          /* voltage of bandgap reference */
+  }
+  else                             /* - */
+  {
+    U = Cfg.Vcc;              /* voltage of Vcc */   
+  }
+
+  /* convert to voltage; */
+  Value *= U;                      /* ADC readings * U_ref */
+//  Value += 511 * Cfg.Samples;      /* automagic rounding */
+  Value /= 1024;                   /* / 1024 for 10bit ADC */
+
+  /* de-sample to get average voltage */
+  Value /= Cfg.Samples;
+  U = (uint16_t)Value;
+
+  return U; 
+}
+
+
+
+/* ************************************************************************
+ *   convenience functions
+ * ************************************************************************ */
+
+
+/*
+ *  wait 5ms and then read ADC
+ *  - same as ReadU()
+ */
+
+uint16_t ReadU_5ms(uint8_t Probe)
+{
+   wait5ms();       /* wait 5ms */
+
+   return (ReadU(Probe));
+}
+
+
+
+/*
+ *  wait 20ms and then read ADC
+ *  - same as ReadU()
+ */
+
+uint16_t ReadU_20ms(uint8_t Probe)
+{
+  wait20ms();       /* wait 20ms */
+
+  return (ReadU(Probe));
+}
+
+
+
+/* ************************************************************************
+ *   clean-up of local constants
+ * ************************************************************************ */
+
+
+/* source management */
+#undef ADC_C
+
+
+
+/* ************************************************************************
+ *   EOF
+ * ************************************************************************ */