hello, can anyone help me how to get a 1 hertz timebase for a ttl digital clock? i already tried to use the 60Hz frequency from a 220VAC outlet and divide it down to 1Hz using a mod60 counter but still not getting that exact 1Hz freq. output...i dont get it...i am really having a hard time on this one. And can you pls include a schematic, i would greatly appreciate any help from you guys.
power company timebases are usually very accurate over the long term. short term they my vary a bit. a "watch crystal" is a good standard for time keeping, or perhaps at less accuracy any common crystal, say a 20 meg hz microcontroller crystal.
First of all, if you have, MM5369 IC available, use it as it provides accurate 60Hz timebase for clocks but might be a bit costly. Otherwise use the following ckt with a 4.9152MHz crystal to get accurate 60Hz timebase. Divide it by 60 using your current divider to Get precise 1Hz timebase. The CD4541 divides the crystal frequency by 8192Hz and then CD 4017 divides the resulting 600Hz by 10 to get 60Hz.
My fav is a CD4060 with a watch crystal (32.768KHz). No external souce needed, though you will need another flip flop. The datasheet has the info. The power company counts cycles during the day, and tweaks their freq to make it come out right. So moment by moment they might be off a little, but by the end of the day it works out.
I've done this for a 1HZ timebase: http://www.josepino.com/?one_second_timebase I also built a 60HZ line-to-1HZ line clock circuit using a 555/4022/4017 circuit. Can't find a link right now. Put both clocks on separate counters and let them run for days. The counts varied form each other as much as +/- 10, but stayed together long term. I think the hacked desk clock was the stable one. Ken
