[HN Gopher] Show HN: Apple II clock using interrupts from physic...
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Show HN: Apple II clock using interrupts from physical pendulum
clock
A clock app for my Apple ][ clone in 6502 assembly, using
interrupts generated by an inductive proximity sensor and a
physical pendulum clock. I wanted to polish the code a bit more
before sharing (I especially dislike the self modifying code part),
but the computer seems to have developed a hardware problem lately
and it keeps crashing (bad RAM chip most likely), so I am sharing
as is.
Author : wkjagt
Score : 98 points
Date : 2024-01-28 15:55 UTC (7 hours ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| mungoman2 wrote:
| Really love this idea and execution. Truly fantastic!
| wkjagt wrote:
| Thanks :D
| guytv wrote:
| This is awesome!
|
| Also, a heads-up to OP: the personal website linked from your
| GitHub account appears to be down.
| wkjagt wrote:
| Thanks! And I forgot I still had that site linked there. I'll
| remove it.
| em3rgent0rdr wrote:
| Interesting idea to use an inductive sensor. I personally would
| have suggested a hall sensor (though that would involve fixing a
| tiny magnet to the pendulum) as the cheapest solution. But of
| course there are many ways to solve the same problem. Neat
| project, thanks for sharing!
| joezydeco wrote:
| My mind went to an optical sensor. Either interrupt a beam with
| the pendulum or attach a small reflector to the arm.
| SomeoneFromCA wrote:
| The canonical way of using pendulums as time reference in
| electronic circuits, is to use magnetic pendulum coupled a
| special circuit (a bjt and an inductor) that would not only
| sense the pendulum but also reenergize it.
|
| example:
| https://electronics.stackexchange.com/questions/685779/elect...
| wkjagt wrote:
| Oh cool I didn't know that existed. In my case I don't have
| to re-energize it because I use an existing mechanical clock.
| zokier wrote:
| If you are curious about this sort of thing, look up master
| pendulum clocks. They were precision clocks that provided
| electric timing pulses to network of slave clocks or other
| uses. Afaik they were common in mid-20th century
| wkjagt wrote:
| Thanks! I liked the inductive sensor, because it meant I didn't
| have to change the physical clock in any way. And they were
| only like 5 CAD each.
| geerlingguy wrote:
| This is quite interesting; I've been reading up on PLL and chip
| design lately, as well as VCOs, TCXOs, etc.
|
| And now I'm wondering how accurate someone could make a reference
| signal from a physical pendulum like this--or what strange quirks
| you could introduce into a system using such a 'weighty' clock
| source!
| tvb wrote:
| Many pendulum clocks are capable of well under 1 ppm accuracy,
| which is better than many quartz oscillators. Here is a tour of
| clock precision by orders of magnitude:
|
| http://leapsecond.com/ten/
|
| Here is a world record setting pendulum clock from a few years
| ago:
|
| http://leapsecond.com/pend/clockb/
|
| Precision pendulum clocks are a very deep rabbit hole.
| zokier wrote:
| See also https://en.wikipedia.org/wiki/Shortt%E2%80%93Synchro
| nome_clo...
|
| > The Shortt was the first clock to be a more accurate
| timekeeper than the Earth itself; it was used in 1926 to
| detect tiny seasonal changes in the Earth's rotation rate.
| Shortt clocks achieved accuracy of around a second per year
|
| If my math is right, thats about 30ppb
| kazinator wrote:
| Wow, people are still working on the problem of the Apple II not
| having an RTC, in some shape? :)
|
| Say, weren't there some issues with interrupts on the Apple II,
| due to both the 6502 as well as buggy ROMs? Basically, none of
| the I/O in the stock system with Apple parts used interrupts
| whatsoever. Not disks, not serial communication.
| wkjagt wrote:
| Yeah I think nothing actually uses interrupts by default. But
| they're accessible through the expansion ports. Not sure what
| the problem would be though.
| noxon wrote:
| Serial interfaces could use interrupts, and it was necessary at
| higher baud rates.
| tonyedgecombe wrote:
| Yes, I remember writing a print spooler using interrupts as
| part of my first job.
| thought_alarm wrote:
| The problem with the original firmware was that its interrupt
| handler used a zero-page location to store the accumulator.
| AppleSoft BASIC uses the same zero-page location for its own
| use, which makes BASIC incompatible with interrupts.
|
| Another problem was with in the original Apple IIe. Its
| firmware interrupt handler was not updated to handle the new
| auxiliary memory and 80-column video configurations.
|
| ProDOS provided proper support for interrupts, even on older
| Apple IIs (needed for mouse-based GUI apps and realtime
| clocks), and the firmware was eventually updated in the IIc and
| Enhanced IIe.
| lisper wrote:
| Related from 1981: https://news.ycombinator.com/item?id=20013486
| wkjagt wrote:
| Oh wow, he uses the 60hz signal from the video circuitry.
| That's way more convenient than a big wall clock ;) And he even
| uses the same interrupt gating idea for the interrupts by using
| the game port.
| lisper wrote:
| He is me :-) And yes, that's exactly right.
| wkjagt wrote:
| Ha, even cooler! Very nice to see :-)
| technothrasher wrote:
| Neat project. But I want more pictures of the mechanical clock
| too. All I can see are the pendulum, weights and chain. I'm going
| to guess it is a German Hermle movement? Is that a custom made
| clock case?
| wkjagt wrote:
| Oh good point, I hadn't even considered posting a photo of the
| clock itself. I'll add a picture of it to the post later. But
| to answer you question: no custom made clock case. The wood
| you're seeing is the wall. And the clock is a Junghans (so
| indeed German), I would say midcentury modern? Almost identical
| to this model (found through Google Images) :
| https://a.1stdibscdn.com/archivesE/upload/1121189/f_13997072...
| jamesbfb wrote:
| The high pitch from the CRT in the video (on GitHub) has my 40
| year old ears feeling pretty happy about themselves!
| wkjagt wrote:
| I am 46 and I don't hear it, not even when I am sitting right
| next to it. But others who I've show the computer to have
| noticed the noise as well, so I know it's there. I'm actually
| kinda happy about not hearing it myself :D
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