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'[PICLIST] Cheap and easy 100 Hz MPU clock?'
2000\11\16@152247 by John Pearson

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I am looking for a cheap and easy 100 Hz clock (yes, 100 cycles per second)
for externally clocking a pic. I considered a 3909, but they are not very
cheap and not that easy to find.

Any ideas?

Thanks

John

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2000\11\16@154402 by severson

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I'd investigate the CMOS version of the 555.

If you are in the US could you get by with 60 Hz or 120Hz from the power
line? If you are in a country with 50Hz power you could get 50/100Hz from
mains.

Does your source need to be as accurate as a crystal?

Care to use a PIC outputting 100Hz to clock your PIC? ;-)

-Rob

> {Original Message removed}

2000\11\16@154820 by Mike Mansheim

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>>
I am looking for a cheap and easy 100 Hz clock (yes, 100 cycles per second)
for externally clocking a pic. I considered a 3909, but they are not very
cheap and not that easy to find.

Any ideas?
<<

how about the grand ole 555 timer?

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2000\11\16@155416 by w. v. ooijen / f. hanneman

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> I am looking for a cheap and easy 100 Hz clock (yes, 100 cycles per
second)
> for externally clocking a pic. I considered a 3909, but they are not very
> cheap and not that easy to find.
>
> Any ideas?
> <<
>
> how about the grand ole 555 timer?

Or a 12C509?

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'[PIC]: Cheap and easy 100 Hz MPU clock? (prefix ad'
2000\11\16@161345 by Barry King

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John,

You asked:

>I am looking for a cheap and easy 100 Hz clock (yes, 100 cycles per
>second) for externally clocking a pic. I considered a 3909, but they
>are not very cheap and not that easy to find.

>Any ideas?

If I wanted to run that slow, I'd use a (CMOS) 4060, with a 32 kHz
watch crystal, and tap off one of the last divider taps.

But if you are doing it so that you use less power than a PIC witha
32 kHz clock, this won't help, since the 4060 will draw the few uA
instead of the PIC LP osc.  What are you trying to do?

-Barry.
------------
Barry King
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
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2000\11\16@172438 by Jinx

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How accurate does the 100Hz have to be ?

Do you actually want a 100Hz clock or 100 ips ?

How are you powering the PIC ?

If you've got access to 50Hz mains then you could use a capacitive
voltage dropper plus a full bridge to get 100Hz (if LV AC isn't
available). The cap might not be cheap if bought, but free if scrounged
from an old PSU. You could power the PIC as well if you then filter the
voltage. Using the mains frequency as a reference is about as good
as you'll get. You'd have to watch isolation safety though if using full
mains HV

AFAIK the duty cycle of an external clock doesn't need to be 50%,
it can be pulses > 5us for LP

"Converting" a hex value to a decimal value with a binary counter
like a 4060 will mean picking a crystal that has decimal and hex
divisors. eg a 4060 divides overall by 8192 so to get 100 at
the last stage means starting with a 819,200Hz crystal. My DC/
AC convertor starts at 4.00MHz and divides down to 100Hz for the
transformer with a bunch of 4017s and a couple of flip-flops. If you
are going to go to that much trouble, use a 12C508 with RC osc
and temperature compensate it (eh Alice ?)

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2000\11\16@172451 by Jinx

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> I considered a 3909, but they are not very cheap and not that
> easy to find.

IIRC they're obsolete

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2000\11\17@045157 by mike

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On Thu, 16 Nov 2000 21:48:06 +0100, you wrote:

>> I am looking for a cheap and easy 100 Hz clock (yes, 100 cycles per
>second)
>> for externally clocking a pic. I considered a 3909, but they are not very
>> cheap and not that easy to find.
>>
>> Any ideas?
>> <<
>>
>> how about the grand ole 555 timer?
>
>Or a 12C509?
For stability, especially over supply voltage changes, an op-amp or
comparator oscillator is very good and very cheap. Assuming that the
reason for clocking so slowly is to save power (can't think of any
other, otherwise you could use a 32k watch crystal), this should also
be more power-efficient than a 555 - I think you can get CMOS
comparators that draw a couple of microamps.
You may also be able to get a micropower reset chip to oscillate with
an R or two and a cap. Beware of the microchip ones, though, as their
internal delay varies a lot - you'd want one with no delay, e.g.
Telcom (oops, noe Microchip!), Seiko etc.
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2000\11\17@161949 by Peter L. Peres

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The lowest power low frequency oscillators are probably LC ;-) But in real
life a sawtooth oscillator or blocking oscillator implemented with a logic
level fet and pulse transformer will probably do it imho. If I'm not wrong
this uses only 5 parts. Ask me again for a schematic.

Peter

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'[EE]: Cheap and easy 100 Hz MPU clock? (prefix add'
2000\11\18@104821 by Bob Ammerman

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> I have always been curious whether in a big country with a unified grid
> centralized timing signalling is used to sync the plants ? Because I think
> that it is very hard to do it otherwise (plants syncing to what they
> 'see' on the outgoing lines) on a grid with significant time lags.

Syncronization to the grid is actually pretty easy. You just have to get
away from the thinking of 'outgoing' lines.

When a plant first comes online, it brings its generator up to speed, and
then waits until it is in phase with the voltage seen on the 'outgoing' line
(which, since the big generator circuit breaker is open, at this point is
just a reference signal). When everything is reasonable (ie: generator
frequency is very close to line frequency, generator voltage is pretty close
to line voltage and generator phase is close to line phase) the generator
breaker is then closed to connect the unit to the grid.

Once the breaker is closed in, there is no way the generator can get out of
phase/frequency lock with the grid.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)


> Peter
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2000\11\18@105857 by staff

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Bob Ammerman wrote:
{Quote hidden}

Takes me back! When I was an apprentice we did some labs on grid-sync,
the ancient system of three light bulbs from our phases to their phases.
As you bring your MG up to sync the lights flash in a circle, getting
slower and slower until they are in phase, then you flip the switch.
Like something out of a 50's horror movie to see it done. :o)

I have noticed that the wind turbine power generators have gotten
smaller for the grid-synched ones now. When the wind blows stronger
than x mph the wind turbine propeller gets close to the right speed,
then a microporcessor "clicks" the relay and connects it to the grid
when it hits the exact speed and phase angle. Pretty cool. Beats having
dc batteries and inverters before you can sell your power. I want a few
of them in my backyard, and a backyard big enough to put them in! :o)
-Roman

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2000\11\18@115415 by dre Domingos F. Souza

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>Once the breaker is closed in, there is no way the generator can get out of
>phase/frequency lock with the grid.

       Why? The frequency of the line is generated by a switcher (as I learned, the mains voltage is generated in DC, and switched to AC in a HUGE bank of SCRs), and there is a PLL locked to the external line frequency?

       It seems to be an interesting subject :o)


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2000\11\18@120234 by Bob Ammerman

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----- Original Message -----
From: Alexandre Domingos F. Souza <spamBeGonexandinhospamBeGonespamINTERLINK.COM.BR>
To: <TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU>
Sent: Saturday, November 18, 2000 11:58 AM
Subject: Re: [EE]: Cheap and easy 100 Hz MPU clock? (prefix added)


>Once the breaker is closed in, there is no way the generator can get out of
>phase/frequency lock with the grid.

       Why? The frequency of the line is generated by a switcher (as I
learned, the mains voltage is generated in DC, and switched to AC in a HUGE
bank of SCRs), and there is a PLL locked to the external line frequency?

       It seems to be an interesting subject :o)


No, DC is only used for _very_ high voltage (typically 500,000Kv and up),
long distance transmission lines (in the US only found spanning the large
distances in the midmest).

Everything else is done with AC.

Once the generator breaker is closed, the low impedence to the grid prevents
the generator from running at any but the exact correct speed.

Actually, the generator tries to 'push' the frequency a little bit, but that
is regulated by the energy control center by adjusting generation system
wide.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2000\11\18@123222 by Bob Ammerman

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> No, DC is only used for _very_ high voltage (typically 500,000Kv and up),
> long distance transmission lines (in the US only found spanning the large
> distances in the midmest).

oops, that should be 500Kv or 500,000V !

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2000\11\19@182537 by Peter L. Peres

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>connect generator when in phase

Bob, thank you for the explanation, but I think that there are some very
serious issues with this. Notice that I asked about very large networks
(with significant time delays). What I see is, that one connects the
generator and then starts putting on power (by pushing the phase a bit
forward). Now, the other generators on the grid will have this as decrease
in load, but after a time delay (caused by the network). They will
regulate down, but the new generator will see this only after the network
delay etc etc. You have generators with gain (in the control loops) and a
long time delay = oscillator. I have seen this happen when large grids
were coupled to each other. We were consumers and we had the voltage go
between 170 and 240V in a nice sinus for several seconds at a time when
they did this ;-) I suspect that in a very large net you DON'T have this
effect. The question was, how come you don't.

Peter

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2000\11\19@190707 by Dwayne Reid

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At 01:02 AM 11/20/00 +0200, Peter L. Peres wrote:
> >connect generator when in phase
>
>Bob, thank you for the explanation, but I think that there are some very
>serious issues with this. Notice that I asked about very large networks
>(with significant time delays). What I see is, that one connects the
>generator and then starts putting on power (by pushing the phase a bit
>forward). Now, the other generators on the grid will have this as decrease
>in load, but after a time delay (caused by the network). They will
>regulate down, but the new generator will see this only after the network
>delay etc etc. You have generators with gain (in the control loops) and a
>long time delay = oscillator. I have seen this happen when large grids
>were coupled to each other. We were consumers and we had the voltage go
>between 170 and 240V in a nice sinus for several seconds at a time when
>they did this ;-) I suspect that in a very large net you DON'T have this
>effect. The question was, how come you don't.

Power system stabilizers.  Fixed purpose control systems that can over-ride
the generator's voltage regulator.  I don't know much about them (others
hear at Trinity know very much about the subject) but I know that they are
quite effective.

dwayne



Dwayne Reid   <RemoveMEdwaynerspamTakeThisOuTplanet.eon.net>
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2000\11\19@213014 by Bob Ammerman

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----- Original Message -----
From: Peter L. Peres <plpEraseMEspam.....ACTCOM.CO.IL>
To: <EraseMEPICLISTspamMITVMA.MIT.EDU>
Sent: Sunday, November 19, 2000 6:02 PM
Subject: [EE]: Cheap and easy 100 Hz MPU clock? (prefix added)


{Quote hidden}

Probably because the effective 'capacitance' (actually is it largely  in the
rotational inertia of the units) so to speak limits how much things can
swing.

Also, there is a _lot_ of sophisticated stuff involved in scheduling load
changes and frequency control changes.

Like any other control loop, great care must be taken to ensure stability.

I have seen one interesting case where the control algorithm at the 2500KW
power plant at Niagara Falls somehow got in resonance with the water
sloshing back and forth in the forebay (the body of water that is the
immediately supply of water to the generators). As the water sloshed to the
generator end of the forebay, the generators started to produce more power
so the control system reduced the water flow, which backed the water up
further at the generator end of the forebay with sloshed back to the far end
of the forebay. As the wave moved back in the forebay the head on the
generators dropped so the system opened the gates a little further, just in
time for the water to slosh back to the generators....

You get the idea. This was noticed because only a couple of the generators
at the plant were 'on reg'. The rest were on a 'fixed gate position' control
mode. The units on reg started swinging back and forth rather rapidly in
time to the water level in the forebay.

I saw the chart recorder outputs and it was uncanny!

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)



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2000\11\20@160631 by Peter L. Peres

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Dwayne Reid wrote:

>Power system stabilizers.  Fixed purpose control systems that can
>over-ride the generator's voltage regulator.  I don't know much about
>them (others hear at Trinity know very much about the subject) but I know
>that they are quite effective.

Thanks, but do they use a signalling system between them (other than the
powerline proper - i.e. carrier current, radio or whatnot) ? Because I
think that it is not possible to do it without this and still keep the
voltage within +/- 5% at load changes.

thanks,

Peter

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2000\11\21@211959 by dre Domingos F. Souza

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>        Why? The frequency of the line is generated by a switcher (as I
>learned, the mains voltage is generated in DC, and switched to AC in a HUGE
>bank of SCRs), and there is a PLL locked to the external line frequency?
>No, DC is only used for _very_ high voltage (typically 500,000Kv and up),
>long distance transmission lines (in the US only found spanning the large
>distances in the midmest).

       Nah, Bob! I said the supply is GENERATED in DC, and after switched to AC, isn't it???

>Once the generator breaker is closed, the low impedence to the grid prevents
>the generator from running at any but the exact correct speed.
>Actually, the generator tries to 'push' the frequency a little bit, but that
>is regulated by the energy control center by adjusting generation system
>wide.

       But how this frequency is generated? Is it generated directly in AC??? I though it was in DC!


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2000\11\21@222815 by Bob Ammerman

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----- Original Message -----
From: Alexandre Domingos F. Souza <RemoveMExandinhoTakeThisOuTspamspamINTERLINK.COM.BR>
To: <EraseMEPICLISTspamspamspamBeGoneMITVMA.MIT.EDU>
Sent: Tuesday, November 21, 2000 9:24 PM
Subject: Re: [EE]: Cheap and easy 100 Hz MPU clock? (prefix added)


>        Why? The frequency of the line is generated by a switcher (as I
>learned, the mains voltage is generated in DC, and switched to AC in a HUGE
>bank of SCRs), and there is a PLL locked to the external line frequency?
>No, DC is only used for _very_ high voltage (typically 500,000Kv and up),
>long distance transmission lines (in the US only found spanning the large
>distances in the midmest).

       Nah, Bob! I said the supply is GENERATED in DC, and after switched
to AC, isn't it???

EVERY SINGLE POWER PLANT I HAVE BEEN IN DIRECTLY GENERATES IN AC AT 60HZ,
WITHOUT EXCEPTION

(sorry 'bout the shouting, but...)

I am not sure about the technology used with the very, very, very high
voltage (500kV+) DC transmission lines used to span large distances.

>Once the generator breaker is closed, the low impedence to the grid
prevents
>the generator from running at any but the exact correct speed.
>Actually, the generator tries to 'push' the frequency a little bit, but
that
>is regulated by the energy control center by adjusting generation system
>wide.

       But how this frequency is generated? Is it generated directly in
AC??? I though it was in DC!

NO, NO a thousand times NO.

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2000\11\21@225420 by dre Domingos F. Souza

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>        Nah, Bob! I said the supply is GENERATED in DC, and after switched
>to AC, isn't it???
>EVERY SINGLE POWER PLANT I HAVE BEEN IN DIRECTLY GENERATES IN AC AT 60HZ,
>WITHOUT EXCEPTION

       Nice! But I learned differently...Of course I found it to be STRANGE, but that's what the teachers said :o)


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