....Yes, of course,.. Thanks, Peter. Jack On 4/22/13, Peter wrote: > Gordon Williams ncf.ca> writes: > >> I calculated 0.25 deg/min (360 deg/day / 1440 min/day =3D 0.25 deg/m= in) >> but maybe there are effects of latitude and date that I'm not >> considering, >> but I don't see that. >> >> Bob was not very specific with "not very bad" and "more severe" >> assertions > > Yes, of course, my bad. Anyway 6 minute intervals make for a neat 8 bit > clock which need not even be microcontroller driven. A little cmos divide= r > chain and a watch xtal and you're set. There was even a hack for ordinary > mains operated led clocks, to mod them for amateur astronomy, the > fractional > correction needed to slow them down to astronomical clock mode was > implemented in hardware using cycle stealing at the 50Hz mains clock leve= l. > > Sidereal day is 86164.091712 seconds vs 86400 calendar day. Spreading tha= t > out evenly works out to 236 and a little seconds to steal, per day, or > almost one for every 6 minute interval in a 6 minute period clock (there > are > 240 6 minute periods in a day), less 4 instances/day, running on 8 bits, > with the fractional part treshed in using some phase accumulator over > several days. of course this can be taken to much higher levels of > refinement but there is no need at this point. There is nothing in this > algorithm which can't run in a lowly 8 bit pic. > > -- Peter > > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .