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Simple ADC code from http://pjrc.com/teensy/adc.html

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1 parent 5448d73 commit 49cbd6b6e2d2a49cba9a6471000a26cfcba1131e WardCunningham committed Jun 11, 2010
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  1. +53 −0 analog.c
  2. +36 −0 analog.h
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+// Simple analog to digitial conversion
+
+#include <avr/io.h>
+#include <avr/pgmspace.h>
+#include <stdint.h>
+#include "analog.h"
+
+
+static uint8_t aref = (1<<REFS0); // default to AREF = Vcc
+
+
+void analogReference(uint8_t mode)
+{
+ aref = mode & 0xC0;
+}
+
+
+// Arduino compatible pin input
+int16_t analogRead(uint8_t pin)
+{
+#if defined(__AVR_ATmega32U4__)
+ static const uint8_t PROGMEM pin_to_mux[] = {
+ 0x00, 0x01, 0x04, 0x05, 0x06, 0x07,
+ 0x25, 0x24, 0x23, 0x22, 0x21, 0x20};
+ if (pin >= 12) return 0;
+ return adc_read(pgm_read_byte(pin_to_mux + pin));
+#elif defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB1286__)
+ if (pin >= 8) return 0;
+ return adc_read(pin);
+#else
+ return 0;
+#endif
+}
+
+// Mux input
+int16_t adc_read(uint8_t mux)
+{
+#if defined(__AVR_AT90USB162__)
+ return 0;
+#else
+ uint8_t low;
+
+ ADCSRA = (1<<ADEN) | ADC_PRESCALER; // enable ADC
+ ADCSRB = (1<<ADHSM) | (mux & 0x20); // high speed mode
+ ADMUX = aref | (mux & 0x1F); // configure mux input
+ ADCSRA = (1<<ADEN) | ADC_PRESCALER | (1<<ADSC); // start the conversion
+ while (ADCSRA & (1<<ADSC)) ; // wait for result
+ low = ADCL; // must read LSB first
+ return (ADCH << 8) | low; // must read MSB only once!
+#endif
+}
+
+
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+#ifndef _analog_h_included__
+#define _analog_h_included__
+
+#include <stdint.h>
+
+void analogReference(uint8_t mode);
+int16_t analogRead(uint8_t pin);
+int16_t adc_read(uint8_t mux);
+
+#define ADC_REF_POWER (1<<REFS0)
+#define ADC_REF_INTERNAL ((1<<REFS1) | (1<<REFS0))
+#define ADC_REF_EXTERNAL (0)
+
+// These prescaler values are for high speed mode, ADHSM = 1
+#if F_CPU == 16000000L
+#define ADC_PRESCALER ((1<<ADPS2) | (1<<ADPS1))
+#elif F_CPU == 8000000L
+#define ADC_PRESCALER ((1<<ADPS2) | (1<<ADPS0))
+#elif F_CPU == 4000000L
+#define ADC_PRESCALER ((1<<ADPS2))
+#elif F_CPU == 2000000L
+#define ADC_PRESCALER ((1<<ADPS1) | (1<<ADPS0))
+#elif F_CPU == 1000000L
+#define ADC_PRESCALER ((1<<ADPS1))
+#else
+#define ADC_PRESCALER ((1<<ADPS0))
+#endif
+
+// some avr-libc versions do not properly define ADHSM
+#if defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB1286__)
+#if !defined(ADHSM)
+#define ADHSM (7)
+#endif
+#endif
+
+#endif

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