Sidereal Clock

siderealClockATmega8.md

About

Here is the controller code for modified movement of automatic planisphere clock by ATmega 8. The original design using PIC is introduced below.

http://cosmic.world.coocan.jp/craft/starclock.htm (google Translate)

Note: Since the star disk data of the above site is for the area of Japan, for other areas, you may want to obtain data from like following site.

https://in-the-sky.org/planisphere/index.php

This code is written with reference to the following information.

• https://www.logre.eu/wiki/Horloge_analogique_24h/en
• https://www.avrfreaks.net/forum/atmega8-timer2-asynchronous-mode-not-working

Code

// Sidereal clock rate pulse for analog clock movement generator
// Programmed by Satoru Takagi
// for ATmega8L
// avrdude -c usbasp -p m8 -B12 -U lfuse:w:0xe1:m -U hfuse:w:0xc9:m -U flash:w:$(TargetName).hex
// Note: for quartz: hfuze=c9
//
// based on
// https://www.logre.eu/wiki/Horloge_analogique_24h/en
// and
// https://www.avrfreaks.net/forum/atmega8-timer2-asynchronous-mode-not-working
// for making
// http://cosmic.world.coocan.jp/craft/starclock.htm
//

/* Output 1PPS on pin 2. */
//#define PPS 

#define F_CPU 1000000
#include <stdint.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>
#include <util/delay.h>

#ifdef PPS
#   define MICROSECONDS_PER_INTERRUPT  1000000
#   define MICROSECONDS_PER_PULSE      1000000
#else
/* Nominally 8e6, but quartz was calibrated to be 6.5 ppm fast. */
//#   define MICROSECONDS_PER_INTERRUPT  7999948 
#   define MICROSECONDS_PER_INTERRUPT  8000555 // Brd.0
//#   define MICROSECONDS_PER_PULSE     24000000 // for 24hr clock
#   define MICROSECONDS_PER_PULSE     23934470 // for sidereal day clock
#endif

#define PULSE_LENGTH 60  /* ms */

void startup_blink(){
	uint8_t count;
    for (count = 0; count < 4; count++) {
	    _delay_ms(200);
	    PORTD = _BV(PD0);
	    _delay_ms(PULSE_LENGTH);
	    PORTD = 0;
	    _delay_ms(200);
	    PORTD = _BV(PD1);
	    _delay_ms(PULSE_LENGTH);
	    PORTD = 0;
    }
}

void init_timer()
{
	startup_blink();						// wait quartz stabilize and startup tick
	ASSR = _BV(AS2);						// Set timer2 to run asynchronous
#ifdef PPS	
	TCCR2 = _BV(CS20) | _BV(CS22);			// Start timer2 with prescaler = 128 (TCNT2 = 255 takes 1 sec.)
#else
	TCCR2 = _BV(CS20) | _BV(CS21) | _BV(CS22);	// Start timer2 with prescaler = 1024 (TCNT2 = 255 takes 8 sec.)	
#endif
	while(ASSR & _BV(TCN2UB));				// Wait until TC2 is updated
	TIMSK = _BV(TOIE2);						// Enable timer2 overflow interrupt
	sei();									// Enable global interrupt
}

ISR(TIMER2_OVF_vect)
{
	
    static long unaccounted_microseconds;
	static uint8_t pin_bit = _BV(PD0);
	static const uint8_t pin_mask = _BV(PD0) | _BV(PD1);

    /* Send pulses at the correct average frequency. */
    unaccounted_microseconds += MICROSECONDS_PER_INTERRUPT;
    if (unaccounted_microseconds < MICROSECONDS_PER_PULSE) return;
    unaccounted_microseconds -= MICROSECONDS_PER_PULSE;
	
	/* Set the OCR2UB flag in ASSR. */
	OCR2 = 0;
	
	
    /* Pulse motor. */
    PORTD = pin_bit;
    _delay_ms(PULSE_LENGTH);
    PORTD = 0;
    pin_bit ^= pin_mask;  /* next time use the other pin  */
	
    /* Wait end of TOSC1 cycle (30.5 us). */
    while (ASSR & _BV(OCR2UB)) {/* wait */}
}

int main(void)
{
	/* Configure PC5, PD0 and PD1 as output. */
	DDRD = _BV(DDD0) | _BV(DDD1);
	
	set_sleep_mode(SLEEP_MODE_PWR_SAVE);

	init_timer();

	while(1){
		//		sleep_enable();
		sleep_mode();
		//		sleep_disable();
	}
	
	return 0;
}

Make Sample images

Note: In an inexpensive movement (100 yen) I used, a good operation was obtained by placing a 100 Ω resistor in series with the solenoid coil. Also, it worked well without attaching external capacitors to the crystal oscillator.