How hard is to build a processor?
in [Embedded]
|
Prev: LCD interfaces
Next: warentest berufsunfähigkeitsversicherung, berufsunfähigkeitsversicherungen vergleich, privathaftpflicht versicherung, volksfürsorge, kündigung berufsunfähigkeitsversicherung,
From: rickman on 28 Feb 2010 07:01 On Feb 27, 11:11 am, Joe Pfeiffer <pfeif...(a)cs.nmsu.edu> wrote: > D Yuniskis <not.going.to...(a)seen.com> writes: > > Hi Joe, > > > Joe Pfeiffer wrote: > >> The clock/calendar I hope to build over the next year or so will be > >> solar. The shadow of a post uniquely determines both date and time, if > >> you look at both angle and length.... > > > Hmmm... is that (really) true? Or, don't you end up with > > *two* date,times for each angle,length? E.g., won't the > > angle,length be the same for HH:MM on the day before and > > after the Summer Solstice? Or, close enough to make it > > near impossible to differentiate? (dunno, I find thinking > > in 3D on astronomical scales difficult :> ) > > Yes, I should have said "just about unique." I wouldn't be at all > surprised to find out the variation with date won't be possible to > distinguish more accurately than a couple of days, too. > > > Like me, at least you'll have plenty of Sun to play with! (NM) > > I like living down here! > -- > As we enjoy great advantages from the inventions of others, we should > be glad of an opportunity to serve others by any invention of ours; > and this we should do freely and generously. (Benjamin Franklin) I'm not sure where I got this image in my mind, but I seem to recall that the motion of the end of the shadow at a given time each day moves in a figure eight over the course of the year. Ok, I got over my laziness and googled it. This is called the "analemma" and is caused by the tilt of the Earth's axis and the elliptical orbit around the sun. This still does not make the position at all times and days unique, but it does help a bit (and hurt since it becomes a lot more complex to label). Rick
From: Paul Keinanen on 28 Feb 2010 08:17 On Fri, 26 Feb 2010 23:06:50 -0700, D Yuniskis <not.going.to.be(a)seen.com> wrote: >Hi Joe, > >Joe Pfeiffer wrote: >> The clock/calendar I hope to build over the next year or so will be >> solar. The shadow of a post uniquely determines both date and time, if >> you look at both angle and length.... > >Hmmm... is that (really) true? Or, don't you end up with >*two* date,times for each angle,length? E.g., won't the >angle,length be the same for HH:MM on the day before and >after the Summer Solstice? Or, close enough to make it >near impossible to differentiate? (dunno, I find thinking >in 3D on astronomical scales difficult :> ) > >Like me, at least you'll have plenty of Sun to play with! (NM) The elevation of the sun varies very little close to the solstice, about the solar diameter (0.5 degrees) at +/-8 days from solstice and only about 12 arc secs at +/- 1 day from the solstice. Various tropospheric refractions can alter the apparent elevation. The refraction is worst close to horizon, so the winter solstice will be worse. Trying to determine sunrise and sun set times is even worse, since average refraction is just slightly less than one degree and can vary quite a bit from day to day (even mirages). The solar elevation changes rapidly close to the equinoxes (about the solar diameter/day), so this is the best time to determine the date. Determining the local solar time is easy, just determine when the sun transmits the meridian (i.e is directly in the South in Northern hemisphere). Some local clocks are required to divide the time until the next solar transit into 24 hours. The time between two transits is not usually 86400 (atomic) seconds, but varies slightly according to the equation of time (which is due to the elliptical orbit of the Earth). Averaging these variation over the year, you can calculate the mean solar time, in which the day is exactly 86400 seconds long. Waiting for a year to determine the mean solar time or using a sufficient accurate local frequency standard, you can determine, if the actual solar day is longer or shorter than 24 hours, which may help some ambiguity problems in the elevation measurements. Determining the date is much harder due to the refractions, but averaging over a sufficient number of measurements (days), this should give relative accurate results at the equinoxes. Once you know the mean solar time and know your longitude, you know the time at the zone meridian (0, 15, 30, 45 ... degrees E/W). Knowing your latitude, you can determine in which country you are in and hence which time zone is actually used at that area. Finally by knowing your date, will allow you to calculate, if daylight saving time should be used :-).
From: Walter Banks on 28 Feb 2010 12:48 Bill Cooke wrote: > Joe Pfeiffer wrote: > >>>> > >>>> http://www.embedds.com/how-hard-is-to-build-a-processor/ > >>> It is a lost art. In the 70's I taught a course that students built > >>> a small computer out of lab modules of TTL chip's. My first > >>> personal computer was micro coded PDP-8 hand built. > >>> > >>> Ram was 1K (bits) parts on a wirewrap board. > >>> > >>> Walter.. > >>> > >>> > >> In 1961 a colleague told me of a machine in a lab at Cornell named > >> CADET, which reputedly stood for "can't add, doesn't even try". > > > > IBM 1620. See http://en.wikipedia.org/wiki/IBM_1620 The IBM 1620 was the first computer I used. It had some interesting features, a BCD machine with variable length data words. I ran a fibonacci series on it to 2000 terms it took 18 hours. A lot of neat things could be done with the math tables which could be set at run time. The math tables were also the target some elaborate pranks in IBM 1620 labs It was also the first computer that I wrote a compiler for. I have a lot of good memories of the 1620. That was a long time ago. Regards, Walter.. -- Walter Banks Byte Craft Limited http://www.bytecraft.com --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: Jasen Betts on 6 Mar 2010 01:43 On 2010-02-27, D Yuniskis <not.going.to.be(a)seen.com> wrote: > Hi Joe, > > Joe Pfeiffer wrote: >> The clock/calendar I hope to build over the next year or so will be >> solar. The shadow of a post uniquely determines both date and time, if >> you look at both angle and length.... > > Hmmm... is that (really) true? yes. > Or, don't you end up with > *two* date,times for each angle,length? that may happen for some dates of some years :) --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: rickman on 8 Mar 2010 13:57
On Mar 6, 1:43 am, Jasen Betts <ja...(a)xnet.co.nz> wrote: > On 2010-02-27, D Yuniskis <not.going.to...(a)seen.com> wrote: > > > Hi Joe, > > > Joe Pfeiffer wrote: > >> The clock/calendar I hope to build over the next year or so will be > >> solar. The shadow of a post uniquely determines both date and time, if > >> you look at both angle and length.... > > > Hmmm... is that (really) true? > > yes. > > > Or, don't you end up with > > *two* date,times for each angle,length? > > that may happen for some dates of some years :) Actually, it happens for every day of every year other than the solstices. The two solstices (actually a day or two on either side depending of the season) has the lowest or highest path across the sky, so no other day will have quite in that same path. But every time of every other day (excluding a few seconds at the start and end of the day when one day has sunshine and the other does not) will match a time of two days, between spring to fall and one between fall to spring. The path of the sun may not be the same on those two days, but each point will map to two different times and days. Rick |