new project

Makefile

@@ -0,0 +1,14 @@
+AVRDUDE_PORT=/dev/ttyUSB0
+#MCU = atmega168
+MCU = attiny45
+
+#F_CPU = 8000000
+F_CPU = 10000000
+
+TARGET = limon
+
+SRC = limon.c
+
+include ../avr-tmpl.mk
+
+

limon.c

@@ -0,0 +1,306 @@
+/*
+ * Simple Li-poly battery monitor
+ */
+
+#include <inttypes.h>
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <avr/sleep.h>
+#include <util/delay.h>
+
+#ifdef __AVR_ATtiny45__
+/* 
+ *@@ Pin assignments for ATtiny45
+ * 
+ * Pins:
+ *
+ * BATI - Battery voltage sense input pint 
+ * LEDA - battery level alert led (red)
+ * LEDB - battery level usable led (orange)
+ * LEDC - battery level good led (yellow)
+ * LEDD - battery level full led (green)
+ *
+ * N.B. Code assumes LED[A-D] are adjacent and LEDA is lowest bit value.
+ *
+ * Interrupts:
+ *
+ * TICK - timer tick from internal timer 1 (clk/16384) = 8MHz/16k + TOP=122 => 4.0023 Hz
+ * ADC  - ADC conversion interrupt
+ */
+
+#define TICK_OCR		OCR1C
+#define TICK_TOP		122
+#define TICK_CLK_DIV_1024	(_BV(CS13)|_BV(CS11)|_BV(CS10))
+#define TICK_CLK_DIV_4096	(_BV(CS13)|_BV(CS12)|_BV(CS10))
+#define TICK_CLK_DIV_16384	(_BV(CS13)|_BV(CS12)|_BV(CS11)|_BV(CS10))
+#define TICK_CLK_MODE		TICK_CLK_DIV_4096
+#define TICK_OVF_VECT		TIM1_OVF_vect
+
+
+// battery voltage level (Vb) input uses Analog input 2 on PB4 (pin 3)
+// Vb/4 via voltage-divider is compared against internal 2.56V reference 
+#define BATI_DDR		DDRB
+#define BATI_PORT		PORTB
+#define BATI_BIT		PB4
+#define BATI_BV			_BV(BATI_BIT)
+
+// primary output is a red "battery dangerously low" alert on PB0
+// secondary output is a three-element bargraph on PB[123]
+#define LED_DDR			DDRB
+#define LED_PORT		PORTB
+#define LED_PIN			PINB
+#define LEDA_BIT		PB0
+#define LEDB_BIT		PB1
+#define LEDC_BIT		PB2
+#define LEDD_BIT		PB3
+
+#define LEDA_BV			_BV(LEDA_BIT)
+#define LEDB_BV			_BV(LEDB_BIT)
+#define LEDC_BV			_BV(LEDC_BIT)
+#define LEDD_BV			_BV(LEDD_BIT)
+#define LEDALL_BV		(LEDA_BV|LEDB_BV|LEDC_BV|LEDD_BV)
+
+
+
+#else
+#error unsupported chip
+#endif
+
+
+/* 
+ *@ Constants 
+ */
+
+/* 
+ * Voltage trigger levels.
+ * Battery voltage is read through a voltage divider.
+ *
+ * if 
+ *    Vin ----+
+ *            R1
+ *            +----- Vout
+ *            R2
+ *            |
+ *            =
+ *            .  (gnd)
+ *
+ * Then Vout = Vin * ( R2 / (R1 + R2) ) 
+ *
+ * 
+ * eg. R1=12k R2=1k => Vout = Vin * (1000 / (1000 + 12000))
+ *                            Vin * 0.0769
+ *
+ *     R1=2k2 R2=1k => Vout = Vin * 0.3125
+ *     R1=3k3 R2=1k => Vout = Vin * 0.232
+ *     R1=3k9 R2=1k => Vout = Vin * 0.204  
+ *     R1=4k7 R2=1k => Vout = Vin * 0.175
+ *
+ * Fully charged LiPo is 4.23v/cell, discharged is 2.7v/cell (nominal voltage 3.7v/cell)
+ * For battery endurance, do not discharge below 3.0v/cell (aircraft users commonly use 2.9v/cell as limit)
+ *
+ * A 3-cell battery (nominally 11.1v) thus varies from 12.9v to 8.1v, with low-volt alert at 9.0v
+ *
+ */
+
+
+// We consider 12v+ to be "full", 11v "good", 10v "low" and 9v "critical" (BMV_foo constants are these values in millivolts)
+//
+// In AVR-worldview, we use 3.9:1 voltage divider (0.204 scale factor), and read 10-bit ADC comparisons versus a 2.56v reference
+// 
+// So 12v becomes 2.448v when divided.   Compared to 2.56v reference this gives an ADC result of 1024*(2.448/2.56) == 979
+// (defun volts2int (v sf) (/ (* 1024.0 (* v sf) ) 2.56))
+//
+#define BMV_FULL 12000
+#define VL_FULL 979
+
+#define BMV_GOOD 11000
+#define VL_GOOD   898
+
+#define BMV_LOW 10000
+#define VL_LOW   816
+
+#define BMV_CRIT 9000
+#define VL_CRIT  734
+
+/* 
+ *@ Global data
+ * 
+ * We take 4 samples (storing results in accumulator) then take an average.
+ *
+ */
+#define SAMPLE_SIZE 4
+char nsample;  // current number of samples in accumulator
+int sum;       // value of accumulator (sum of samples)
+int level;     // voltage level (mean of previous sample set)
+
+/* 
+ *@ Application functions 
+ */
+
+void update_leds(unsigned int level) 
+{
+	unsigned char leds = LED_PORT;
+	leds &= ~LEDALL_BV;
+
+	if (level >= VL_FULL)
+	{
+		// battery full
+		leds |= (LEDB_BV|LEDC_BV|LEDD_BV);
+	}
+	else if (level >= VL_GOOD) 
+	{
+		// battery good
+		leds |= LEDB_BV|LEDC_BV;
+	}
+	else if (level >= VL_LOW) 
+	{
+		// battery low
+		leds |= LEDB_BV;
+	}
+	else
+	{
+		// battery critical
+		leds |= LEDA_BV;
+	}
+	LED_PORT = leds;
+}
+
+/* 
+ *@ Interrupt Service routins
+ *
+ * At every clock interrupt we trigger an ADC input
+ */
+ISR(TICK_OVF_VECT)	
+{
+	/* 
+	 * We got our 1/4 second interrupt
+	 * 
+	 * Kick of an ADC and go back to sleep, the conversion-complete interrupt will do the rest
+	 */
+
+	// write a 1 to ADSC, bit stays high till conversion complete, then goes low, triggering interrupt
+	// conversion will take around 0.1ms (13 ADC clock cycles at 125kHz ADclk)
+	ADCSRA |= ADSC;
+}
+
+/* 
+ * Interrupt service routine for Analog-to-Digital Conversion Complete
+ *
+ * We only ever use the one ADC channel (channel 2, PB4).
+ */
+ISR(ADC_vect)
+{
+	unsigned int v;
+	/* 
+	 * An analog-to-digital conversion for pin BATI_BIT (PB0) has completed
+	 */
+
+	// read 10-bit value from ADCH:ADCL.  MUST read low-byte first
+	v = ADCL;
+	v |= (ADCH << 8);
+	sum += v;
+	++nsample;
+	if (nsample >= SAMPLE_SIZE) 
+	{
+		// we have a full set of samples, calculate mean
+		level = sum/nsample;
+		update_leds(level);
+		nsample=0;
+	}
+}
+
+
+/* 
+ *@ IO init 
+ */
+void
+ioinit (void)	
+{
+	char i;
+	unsigned char l;
+	short v;
+
+	/* 
+	 * Set up BATI pin as analog input
+	 */
+	BATI_DDR &= ~BATI_BV;
+	DIDR0 |= ADC2D; // disable digital input buffer on PB4
+
+	/* 
+	 * Set up all LED pins as ouputs
+	 *
+	 * For debug, cycle a pattern across all leds for 1s
+	 */
+	LED_DDR |= LEDALL_BV;
+	LED_PORT &= LEDALL_BV;
+
+	for (v=LEDA_BV,i=0; i<100; i++) {
+		l = LED_PORT;
+		l &= LEDALL_BV;
+		l |= v;
+		LED_PORT=v;
+		// v is bitmask of a left-rotating single-LED-on pattern
+		v <<= 1;
+		if (v > LEDD_BV) 
+			v = LEDA_BV;
+		_delay_ms(10);
+	}
+	LED_PORT &= ~(LEDALL_BV);
+
+	/* 
+	 * Set up timer 1 as clock tick source
+	 *
+	 * FIXME: really could disable timer interrupts altogether and 
+	 * set ADC to triggerr from timer compare match
+	 */
+	TCCR1 |= _BV(PWM1A); // clear timer on OCR1C match, generate overflow interrupt
+	TCCR1 |= TICK_CLK_MODE; // prescaler divider 16384
+	TICK_OCR = TICK_TOP;
+	TIMSK |= _BV(TOIE1); // overflow interrupt enable 
+
+	/* 
+	 * Set up analog-to-digital converter 
+	 */
+	// set reference level by setting REFS2..0 in ADMUX 
+	// select 2.56v with no external bypass capacitor
+	ADMUX |= REFS2|REFS1;
+
+	// select channel by writing MUX3..0 in ADMUX
+	// we want channel 2 (PB4, pin 3)
+	ADMUX |= MUX1; // 0010 == channel 2
+
+	// set ADC clock prescaler -
+	// we have 8MHz clock, we want 50-200kHz ADclk
+	// Select divisor 64 (0b110), giving 125kHz
+	ADCSRA |= ADPS2|ADPS1;
+
+	// enable ADC unit by settting ADEN in ADCSRA
+	ADCSRA |= ADEN;
+
+	// perform one (polled) conversion and discard result
+	// (first conversion after ADC enable is less accurate than subsequent)
+	ADCSRA |= ADSC;
+	LED_PORT |= LEDA_BV;
+	while (ADCSRA & ADSC)
+		_delay_ms(1);
+	LED_PORT &= ~LEDA_BV;
+
+	// enable ADC interrupts
+	ADCSRA |= ADIE;
+
+	sei ();
+}
+
+int
+main (void)
+{
+	// led off initially
+
+	ioinit ();
+
+	/* loop forever, the interrupts are doing the rest */
+	for (;;)
+		sleep_mode();
+
+	return (0);
+}