60Hz timebase clock

[astouffer]

Amoque: Using the 60Hz power for a source will give me more accuracy than an RTC chip and be cheaper. I actually built a large clock based on the link you posted. It worked great but requires long term tweaking for accuracy. Even a 20ppm crystal it still gained a minute or two every month. Here is me testing one of the digits

This code runs on a 16F684 and blinks an LED on pin 10 at 1Hz when fed a 60Hz input on pin 11. Of course the final version will be doing much more than blinking an led. I plan to use four IV-9 numitron tubes for the digits. http://hackadaycom.files.wordpress.c...2/numitron.jpg

@	__CONFIG _FOSC_INTOSCIO & _WDTE_OFF & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF & _CP_OFF & _CPD_OFF & _BOD_OFF & _BOREN_OFF & _IESO_OFF & _FCMEN_OFF


OSCCON = %01110101			'Internal OSC 8MHz
DEFINE OSC 8				'8MHz
PORTA = 0					'All low
TRISA = %00000100			'Porta.2 input
ANSEL = 0					'No analog
WPUA = 0					'Weak pull up off
CMCON0 = %00000111			'Comparators off and I/O is digital
ADCON0 = 0					'A/D is off
CCP1CON = 0					'PWM and CCP off
OPTION_REG = %11111000		'Timer0 on
TMR0 = 195					'Preload so it rolls over on the 60th pulse
INTCON = %11100000			'INTCON.2 overflow bit

on interrupt goto blink

main:
	@ NOP
	goto main

disable

blink:
toggle portc.0
TMR0=195
INTCON.2 = 0
resume
enable

end

Almost forgot the basic schematic. Use a scope to see what resistor values give you the best output. My meter read 3mA going into a 4N25 optic isolator. http://i.imgur.com/fHWGJHr.jpg