3 ms·

Grabbing the mains to get a 60hz clock is a mutch older hack, pdp11s did that before apple 2s did this,and I'm sure others did it before DEC did

matthewowen 7y ago
Fun things happen if you do this and run your hardware outside the US: most countries use 50hz mains AC.
- Someone 7y ago
  Fun things also happen if that frequency isn’t what you think it is. EU clocks derived from the 50Hz signal, for example, ran up to 6 minutes slow in March 2018 (https://www.theverge.com/2018/3/8/17095440/europe-clocks-running-slow-electricity-frequency-kosovo-serbia https://www.theverge.com/2018/3/8/17095440/europe-clocks-run...) And of course, it also is “fun” when you accidentally do not only pick up the frequency of mains power, but also its voltage in your electronics.
- segfaultbuserr 7y ago
  That's why PDP computers come with a 50 Hz version and 60 Hz version.
couchand 7y ago
I would not call that a hack: many timekeeping systems rely on this principle. There was a great write up on Hackaday: https://hackaday.com/2018/03/29/ask-hackaday-is-your-clock-tied-to-mains-frequency/ https://hackaday.com/2018/03/29/ask-hackaday-is-your-clock-t...
howard941 7y ago
This good technique - I hate to call it a hack because it's been either a legal or aspirational standard for decades - is on its last legs in the US as the NERC has or will retire the error corrections that ensured corrections for long term accuracy. Our principal engineer with a history in the power transformer industry tells stories about better times pre 9/11 when utilities would give tours to engineers and describe how the operators would run line frequency corrections overnight to match the dual clocks present, one showing official time, the other showing the usually slightly slower time reflecting the errors accumulated over the day. http://www.nerc.com/pa/Stand/Project%2020101422%20Phase%202%20of%20BARC%20%20BAL004%20DL/BAL-004-0_White_Paper_Clean_09242015.pdf http://www.nerc.com/pa/Stand/Project%2020101422%20Phase%202%... http://www.msnbc.msn.com/id/43532031/ns/technology_and_science-innovation/t/power-grid-experiment-could-confuse-electric-clocks/ http://www.msnbc.msn.com/id/43532031/ns/technology_and_scien...
- Taniwha 7y ago
  We used to get power from a local hydro project, at the power station they used to (ie prior to ubiquitous computers and all that) have two clocks on the wall, one on the local grid and one on the national grid, periodically they would manually speed things up locally to keep the clocks close together as possibly
Zardoz84 7y ago
NTSC uses 30 FPS because it's half of it. The same reason is why PAL uses 25fps as on Europe we have 50 Hz on the grid
- Taniwha 7y ago
  well technically they use this to reduce hum based interference (the alternative is a slowly rolling hum bar through the screen)

matthewowen 7y ago

Fun things happen if you do this and run your hardware outside the US: most countries use 50hz mains AC.

Someone 7y ago
Fun things also happen if that frequency isn’t what you think it is. EU clocks derived from the 50Hz signal, for example, ran up to 6 minutes slow in March 2018 (https://www.theverge.com/2018/3/8/17095440/europe-clocks-running-slow-electricity-frequency-kosovo-serbia https://www.theverge.com/2018/3/8/17095440/europe-clocks-run...) And of course, it also is “fun” when you accidentally do not only pick up the frequency of mains power, but also its voltage in your electronics.
segfaultbuserr 7y ago
That's why PDP computers come with a 50 Hz version and 60 Hz version.

couchand 7y ago

I would not call that a hack: many timekeeping systems rely on this principle. There was a great write up on Hackaday: https://hackaday.com/2018/03/29/ask-hackaday-is-your-clock-tied-to-mains-frequency/ https://hackaday.com/2018/03/29/ask-hackaday-is-your-clock-t...

howard941 7y ago

This good technique - I hate to call it a hack because it's been either a legal or aspirational standard for decades - is on its last legs in the US as the NERC has or will retire the error corrections that ensured corrections for long term accuracy. Our principal engineer with a history in the power transformer industry tells stories about better times pre 9/11 when utilities would give tours to engineers and describe how the operators would run line frequency corrections overnight to match the dual clocks present, one showing official time, the other showing the usually slightly slower time reflecting the errors accumulated over the day. http://www.nerc.com/pa/Stand/Project%2020101422%20Phase%202%20of%20BARC%20%20BAL004%20DL/BAL-004-0_White_Paper_Clean_09242015.pdf http://www.nerc.com/pa/Stand/Project%2020101422%20Phase%202%... http://www.msnbc.msn.com/id/43532031/ns/technology_and_science-innovation/t/power-grid-experiment-could-confuse-electric-clocks/ http://www.msnbc.msn.com/id/43532031/ns/technology_and_scien...

Taniwha 7y ago
We used to get power from a local hydro project, at the power station they used to (ie prior to ubiquitous computers and all that) have two clocks on the wall, one on the local grid and one on the national grid, periodically they would manually speed things up locally to keep the clocks close together as possibly

Zardoz84 7y ago

NTSC uses 30 FPS because it's half of it. The same reason is why PAL uses 25fps as on Europe we have 50 Hz on the grid

Taniwha 7y ago
well technically they use this to reduce hum based interference (the alternative is a slowly rolling hum bar through the screen)