Author Topic: clock beat generator  (Read 11096 times)

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Offline IanB

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Re: clock beat generator
« Reply #25 on: February 11, 2012, 11:43:45 pm »
dividing from mains frequency is just horrible, its a 0.2% tolerance

The mains frequency in the UK used to be required by law to keep perfect time. It has been very common for mains powered clocks to get their timing from the mains. I believe the power companies are trying to get that standard relaxed now, but as far as I know it remains a pretty good time reference for clocks.

For Simon my first thought would have been to get the mains frequency and divide it down. It only needs discrete circuitry, not even an MCU.
I'm not an EE--what am I doing here?
 

Offline ejeffrey

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Re: clock beat generator
« Reply #26 on: February 11, 2012, 11:57:51 pm »
dividing from mains frequency is just horrible, its a 0.2% tolerance,

In the US and Europe mains frequency is controlled by atomc clocks.  There can be short term fluctuations where short term could be weeks. Over the long term it is more stable than any crystal.  If you plug your clock in and set it while the grid is a couple of minutes behind, it will gradually slew forward and then stay permanently a few minutes fast.
 

Online Rerouter

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Re: clock beat generator
« Reply #27 on: February 12, 2012, 12:30:48 am »
well atleast its offset here, all the grid connected solar inverters really mess with the grid in aus, not just voltage but frequency,
 

Offline Simon

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Re: clock beat generator
« Reply #28 on: February 12, 2012, 11:30:42 am »
dividing from mains frequency is just horrible, its a 0.2% tolerance

The mains frequency in the UK used to be required by law to keep perfect time. It has been very common for mains powered clocks to get their timing from the mains. I believe the power companies are trying to get that standard relaxed now, but as far as I know it remains a pretty good time reference for clocks.

For Simon my first thought would have been to get the mains frequency and divide it down. It only needs discrete circuitry, not even an MCU.

I was starting to consider that but now i also need a very small duty cycle although I guess a monostable can sort that (555).

The clock coil does use 0.17 to 0.22 amps so I also need to look carefully at power consumption and the type of batteries I use.

the original setup of this clock in a firestation was that there were a number of clocks in series connected to a battery and a switch that was worked by a pendulum to give the timing. Obviously the timing bit was the more expensive so it was easier to wire all clocks in series and used one central reference. The battery voltage is unknown and i guess was possibly changed according to how many clocks were in series so that is probably why there is a min/max spec for the coil on the back of it
 

Offline SeanB

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Re: clock beat generator
« Reply #29 on: February 12, 2012, 01:43:46 pm »
Simple method is to take a clock ( Cheap single cell wall clock is perfect, and looks of the clock don't matter here) and rip apart the clock mechanism, to get the small PCB with the crystal, divider and clock driver out of it. Make a note of which pads go where. Power it from a 1.5V supply ( a resistor driving a red LED and a 100uF bypass capacitor) and use a single NPN transistor with a 10k base resistor and 10k collector resistor as a level shifter. Gives a simple source of pulses at 2 second intervals, now you just use 2 4017's to divide by 5 and 3 respectively, using the output from 2 ( or 1) from the second divider to trigger a 0.5 second monostable to drive the clock coil.  Being a slave clock in a master slave system you probably will need a simple 24V DC supply to drive the coil, which does not need to be regulated, an 18VAC transformer and a bridge with 1000uF/50V capacitor will work fine . Use a 7812 to make 12V for the dividers, and drive the clock from the 12V rail, the LED will double as a power indicator.
 

Offline siliconmix

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Re: clock beat generator
« Reply #30 on: February 12, 2012, 05:07:13 pm »
dividing from mains frequency is just horrible, its a 0.2% tolerance

The mains frequency in the UK used to be required by law to keep perfect time. It has been very common for mains powered clocks to get their timing from the mains. I believe the power companies are trying to get that standard relaxed now, but as far as I know it remains a pretty good time reference for clocks.

For Simon my first thought would have been to get the mains frequency and divide it down. It only needs discrete circuitry, not even an MCU.

I was starting to consider that but now i also need a very small duty cycle although I guess a monostable can sort that (555).

The clock coil does use 0.17 to 0.22 amps so I also need to look carefully at power consumption and the type of batteries I use.

the original setup of this clock in a firestation was that there were a number of clocks in series connected to a battery and a switch that was worked by a pendulum to give the timing. Obviously the timing bit was the more expensive so it was easier to wire all clocks in series and used one central reference. The battery voltage is unknown and i guess was possibly changed according to how many clocks were in series so that is probably why there is a min/max spec for the coil on the back of it

make a extra special job of it simon and drop one of these in there.use the pic to decode the signals
http://www.ebay.co.uk/itm/MSF-Atomic-Clock-Receiver-Module-Rugby-Atomic-Clock-/230740011322?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item35b92d293a#ht_2314wt_932
 

Offline Simon

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Re: clock beat generator
« Reply #31 on: February 12, 2012, 05:33:20 pm »
no sure I need to go that far lol
 

Offline IanB

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Re: clock beat generator
« Reply #32 on: February 12, 2012, 05:58:45 pm »
the original setup of this clock in a firestation was that there were a number of clocks in series connected to a battery and a switch that was worked by a pendulum to give the timing. Obviously the timing bit was the more expensive so it was easier to wire all clocks in series and used one central reference. The battery voltage is unknown and i guess was possibly changed according to how many clocks were in series so that is probably why there is a min/max spec for the coil on the back of it

That was a very common thing once upon a time--I think it was called a master clock system. My school had such a system and probably every other school did too. It permitted every clock in every building to show exactly the same time, so all the lessons could keep to the same timetable and start and end exactly on cue. You would find clock systems like that in offices, factories, stations, everywhere. I'm not sure its even obsolete today because even quartz clocks can't keep time that accurately. And imagine if you had to go around and manually adjust dozens of clocks to adjust them, rather than just adjusting the central master clock?
I'm not an EE--what am I doing here?
 

Offline siliconmix

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Re: clock beat generator
« Reply #33 on: February 12, 2012, 06:00:51 pm »
the rugby signal is still used it's on digital watches and weather clocks
 

Offline Simon

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Re: clock beat generator
« Reply #34 on: February 12, 2012, 06:11:14 pm »
the original setup of this clock in a firestation was that there were a number of clocks in series connected to a battery and a switch that was worked by a pendulum to give the timing. Obviously the timing bit was the more expensive so it was easier to wire all clocks in series and used one central reference. The battery voltage is unknown and i guess was possibly changed according to how many clocks were in series so that is probably why there is a min/max spec for the coil on the back of it

That was a very common thing once upon a time--I think it was called a master clock system. My school had such a system and probably every other school did too. It permitted every clock in every building to show exactly the same time, so all the lessons could keep to the same timetable and start and end exactly on cue. You would find clock systems like that in offices, factories, stations, everywhere. I'm not sure its even obsolete today because even quartz clocks can't keep time that accurately. And imagine if you had to go around and manually adjust dozens of clocks to adjust them, rather than just adjusting the central master clock?

Sadly this is a single clock hence he needs the timing generator.
 


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