1 /* Copyright 2015 Jack Humbert
3 * This program is free software: you can redistribute it and/or modify
4 * it under the terms of the GNU General Public License as published by
5 * the Free Software Foundation, either version 2 of the License, or
6 * (at your option) any later version.
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11 * GNU General Public License for more details.
13 * You should have received a copy of the GNU General Public License
14 * along with this program. If not, see <http://www.gnu.org/licenses/>.
17 // Simple analog to digitial conversion
20 #include <avr/pgmspace.h>
24 static uint8_t aref = (1 << REFS0); // default to AREF = Vcc
26 void analogReference(uint8_t mode) { aref = mode & 0xC0; }
28 // Arduino compatible pin input
29 int16_t analogRead(uint8_t pin) {
30 #if defined(__AVR_ATmega32U4__)
31 static const uint8_t PROGMEM pin_to_mux[] = {0x00, 0x01, 0x04, 0x05, 0x06, 0x07, 0x25, 0x24, 0x23, 0x22, 0x21, 0x20};
32 if (pin >= 12) return 0;
33 return adc_read(pgm_read_byte(pin_to_mux + pin));
34 #elif defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB1286__)
35 if (pin >= 8) return 0;
43 int16_t adc_read(uint8_t mux) {
44 #if defined(__AVR_AT90USB162__)
49 ADCSRA = (1 << ADEN) | ADC_PRESCALER; // enable ADC
50 ADCSRB = (1 << ADHSM) | (mux & 0x20); // high speed mode
51 ADMUX = aref | (mux & 0x1F); // configure mux input
52 ADCSRA = (1 << ADEN) | ADC_PRESCALER | (1 << ADSC); // start the conversion
53 while (ADCSRA & (1 << ADSC))
55 low = ADCL; // must read LSB first
56 return (ADCH << 8) | low; // must read MSB only once!