accurate 2Hz generator <1mA supply

[Steve C]

Dear all,
I am looking for a way of producing a 2Hz square wave signal (or just 2hz
pulses of any amplitude really) in a very small package powered from a 2.1V
coin cell lithium battery or 12V, with ~1ppm variation. drift rather than
precision is important (ie it doesn't have to be exactly 2Hz, as long as it
is consistent)

why?:
I am building a man-overboard sensor for a small boat. each of 10 people
carries a small keyfob transmitter, which transmits every 5 seconds to reset
a watchdog timer. Water contact, out of range or a switch will stop
transmission and trigger an alarm.

To prevent the transmitters transmitting over the top of each other I wish
them to each transmit 0.5 seconds apart and staggered. To do this I need an
accurate(less than 1s per day or better) 2hz clock signal so that (once I
have sync'd each of the transmitters) they will maintain their transmission
separation over at least a day. ( each transmitter will trigger from a
different leg of a decade counter) . the transmitters will all plug in to a
base station at the beginning of the day to reset the clocks to sync them)

I am restricted with space as I want it to fit in a keyfob transmitter, and
am restricted by power - the transmitter works off an AA-style 12V cell, but
I don't mind the clock circuit running off a coin cell.

Philips do a range of watch chips: eg
http://www.semiconductors.philips.com/acrobat/datasheets/PCA16XX_3.pdf
but they output 1Hz (0.5 Hz if you only count the +ve parts of the cycle)
and are a pain to program.
I can't find these for sale anywhere either (UK), as I was thinking of using
a higher freq xtal to speed it up if I could get hold of one. (if this would
work)

Has anyone got any sources of low power chips for precise timing like the
philips chip?. it would be great if they could work from 12V too. they need
to be resettable so I can sync them
.. In a perfect world they would interface with the decade counter too but I
can sort that out.
If all else fails, does anyone know of a source of these philips chips
(PCA2002T/1 looks good)

I would be grateful of any feedback!

many thanks

Steve
Manchester, UK
spam@stevecowley.com (change_spam@_to_electronics@ to reply)

 

[Robert C Monsen]

"Steve C" &lt;spam@stevecowley.com&gt; wrote in message
news:G5tZb.60$xx3.46@newsfe1-win...

Dear all,
I am looking for a way of producing a 2Hz square wave signal (or just 2hz
pulses of any amplitude really) in a very small package powered from a
2.1V
coin cell lithium battery or 12V, with ~1ppm variation. drift rather than
precision is important (ie it doesn't have to be exactly 2Hz, as long as
it
is consistent)

why?:
I am building a man-overboard sensor for a small boat. each of 10 people
carries a small keyfob transmitter, which transmits every 5 seconds to
reset
a watchdog timer. Water contact, out of range or a switch will stop
transmission and trigger an alarm.

To prevent the transmitters transmitting over the top of each other I wish
them to each transmit 0.5 seconds apart and staggered. To do this I need
an
accurate(less than 1s per day or better) 2hz clock signal so that (once I
have sync'd each of the transmitters) they will maintain their
transmission
separation over at least a day. ( each transmitter will trigger from a
different leg of a decade counter) . the transmitters will all plug in to
a
base station at the beginning of the day to reset the clocks to sync them)

I suspect that keeping the units synced (and remembering to sync them) will
be a challenge. Also, they would need to have separate 'configuration' to
tell them how many ticks to wait.

However, a simpler thing might be to make each unit a transponder. Then, you
could encode a unit address in the transponder query, or use a different
frequency for each fob. That way, you could figure out which guy was
drowning, and you wouldn't have such close ties, you wouldn't have to 'sync'
the fobs, etc. However, it would complicate the fob, because each of them
would now need to have a receiver as well as a transmitter.

You might be able to buy the radio technology in the form of a chip.

Regards,
Bob Monsen

 

[Bob Stephens]

On Fri, 20 Feb 2004 20:17:53 GMT, Robert C Monsen wrote:

"Steve C" &lt;spam@stevecowley.com&gt; wrote in message
news:G5tZb.60$xx3.46@newsfe1-win...
Dear all,
I am looking for a way of producing a 2Hz square wave signal (or just 2hz
pulses of any amplitude really) in a very small package powered from a
2.1V
coin cell lithium battery or 12V, with ~1ppm variation. drift rather than
precision is important (ie it doesn't have to be exactly 2Hz, as long as
it
is consistent)

why?:
I am building a man-overboard sensor for a small boat. each of 10 people
carries a small keyfob transmitter, which transmits every 5 seconds to
reset
a watchdog timer. Water contact, out of range or a switch will stop
transmission and trigger an alarm.

To prevent the transmitters transmitting over the top of each other I wish
them to each transmit 0.5 seconds apart and staggered. To do this I need
an
accurate(less than 1s per day or better) 2hz clock signal so that (once I
have sync'd each of the transmitters) they will maintain their
transmission
separation over at least a day. ( each transmitter will trigger from a
different leg of a decade counter) . the transmitters will all plug in to
a
base station at the beginning of the day to reset the clocks to sync them)



I suspect that keeping the units synced (and remembering to sync them) will
be a challenge. Also, they would need to have separate 'configuration' to
tell them how many ticks to wait.

However, a simpler thing might be to make each unit a transponder. Then, you
could encode a unit address in the transponder query, or use a different
frequency for each fob. That way, you could figure out which guy was
drowning, and you wouldn't have such close ties, you wouldn't have to 'sync'
the fobs, etc. However, it would complicate the fob, because each of them
would now need to have a receiver as well as a transmitter.

You might be able to buy the radio technology in the form of a chip.

Regards,
Bob Monsen

www.linxtechnologies.com has addressable key fob transmitters.

Bob

BTW is it just me or is fob a really silly word?

 

[Rene Tschaggelar]

Steve C wrote:

Dear all,
I am looking for a way of producing a 2Hz square wave signal (or just 2hz
pulses of any amplitude really) in a very small package powered from a 2.1V
coin cell lithium battery or 12V, with ~1ppm variation. drift rather than
precision is important (ie it doesn't have to be exactly 2Hz, as long as it
is consistent)

why?:
I am building a man-overboard sensor for a small boat. each of 10 people
carries a small keyfob transmitter, which transmits every 5 seconds to reset
a watchdog timer. Water contact, out of range or a switch will stop
transmission and trigger an alarm.

To prevent the transmitters transmitting over the top of each other I wish
them to each transmit 0.5 seconds apart and staggered. To do this I need an
accurate(less than 1s per day or better) 2hz clock signal so that (once I
have sync'd each of the transmitters) they will maintain their transmission
separation over at least a day. ( each transmitter will trigger from a
different leg of a decade counter) . the transmitters will all plug in to a
base station at the beginning of the day to reset the clocks to sync them)

I am restricted with space as I want it to fit in a keyfob transmitter, and
am restricted by power - the transmitter works off an AA-style 12V cell, but
I don't mind the clock circuit running off a coin cell.

Philips do a range of watch chips: eg
http://www.semiconductors.philips.com/acrobat/datasheets/PCA16XX_3.pdf
but they output 1Hz (0.5 Hz if you only count the +ve parts of the cycle)
and are a pain to program.
I can't find these for sale anywhere either (UK), as I was thinking of using
a higher freq xtal to speed it up if I could get hold of one. (if this would
work)

Has anyone got any sources of low power chips for precise timing like the
philips chip?. it would be great if they could work from 12V too. they need
to be resettable so I can sync them
. In a perfect world they would interface with the decade counter too but I
can sort that out.
If all else fails, does anyone know of a source of these philips chips
(PCA2002T/1 looks good)

I would be grateful of any feedback!

A normal quartz does 100ppm over the temperature range.
1ppm is already a better one. Perhaps doable with an
SC cut oscillator.
Couldn't you modulate the signals to keep them apart ?

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
&amp; commercial newsgroups - http://www.talkto.net

 

[Michael Black]

"Steve C" (spam@stevecowley.com) writes:

why?:
I am building a man-overboard sensor for a small boat. each of 10 people
carries a small keyfob transmitter, which transmits every 5 seconds to reset
a watchdog timer. Water contact, out of range or a switch will stop
transmission and trigger an alarm.

So is this a design question, or a basic question? It can't

be hard to decide which, and post to the appropriate newsgroup.

The problem with a lot of design is that people set out with a solution,
when they should be looking at alternatives before they try to set it
in stone.

If it's so risky that someone is likely to fall overboard, I sure
wouldn't trust something homemade, at least not something asked
in a basics newsgroup, by someone who already knows the solution.

If it's so risky that someone is likely to fall overboard, then
surely a harness should be in place. That would keep them from
falling overboard.

But once in harness, then it would be really easy to run two wires
to each person. It's shorted at the person, and properly secured.
Meanwhile, there is a burglar alarm or something in a central location
that the wires run back to.

Someone falls overboard. The wire breaks because they have gone further
than the wire reaches. This means there is no longer continuity between
the wires, and the alarm goes off. "Many overboard". The boat stops,
and they search for him.

Michael

 

[Rene Tschaggelar]

Michael Black wrote:

"Steve C" (spam@stevecowley.com) writes:

why?:
I am building a man-overboard sensor for a small boat. each of 10 people
carries a small keyfob transmitter, which transmits every 5 seconds to reset
a watchdog timer. Water contact, out of range or a switch will stop
transmission and trigger an alarm.


So is this a design question, or a basic question? It can't
be hard to decide which, and post to the appropriate newsgroup.

The problem with a lot of design is that people set out with a solution,
when they should be looking at alternatives before they try to set it
in stone.

If it's so risky that someone is likely to fall overboard, I sure
wouldn't trust something homemade, at least not something asked
in a basics newsgroup, by someone who already knows the solution.

If it's so risky that someone is likely to fall overboard, then
surely a harness should be in place. That would keep them from
falling overboard.

But once in harness, then it would be really easy to run two wires
to each person. It's shorted at the person, and properly secured.
Meanwhile, there is a burglar alarm or something in a central location
that the wires run back to.

Someone falls overboard. The wire breaks because they have gone further
than the wire reaches. This means there is no longer continuity between
the wires, and the alarm goes off. "Many overboard". The boat stops,
and they search for him.

Seconded.
In addition to that, I'd wish a transmitter. Stopping the boat
and do a search may not be that simple. It could be night,
have high winds, 5m waves, heavy rain.
A 70cm (430MHz) transmitter would be a good start. Keyfob toys
are somewhat unuseable for that purpose.

Rene

 

[Michael Black]

Rene Tschaggelar (none@none.net) writes:

Seconded.
In addition to that, I'd wish a transmitter. Stopping the boat
and do a search may not be that simple. It could be night,
have high winds, 5m waves, heavy rain.
A 70cm (430MHz) transmitter would be a good start. Keyfob toys
are somewhat unuseable for that purpose.

Rene

Don't they even have those already? I have this feeling I've seen
such beacons in magazines, complete with a strobe or something so
you will be seen.

You're right, that likely is more important than knowing someone has
fallen overboard, though I suppose it's possible for someone to
fall off and never be noticed. You want to be noticed, and found
in the water while your life preserver is keeping you afloat.

Michael

 

[Mac]

On Fri, 20 Feb 2004 19:20:07 +0000, Steve C wrote:

Dear all,
I am looking for a way of producing a 2Hz square wave signal (or just 2hz
pulses of any amplitude really) in a very small package powered from a 2.1V
coin cell lithium battery or 12V, with ~1ppm variation. drift rather than
precision is important (ie it doesn't have to be exactly 2Hz, as long as it
is consistent)

why?:
I am building a man-overboard sensor for a small boat. each of 10 people
carries a small keyfob transmitter, which transmits every 5 seconds to reset
a watchdog timer. Water contact, out of range or a switch will stop
transmission and trigger an alarm.

To prevent the transmitters transmitting over the top of each other I wish
them to each transmit 0.5 seconds apart and staggered. To do this I need an
accurate(less than 1s per day or better) 2hz clock signal so that (once I
have sync'd each of the transmitters) they will maintain their transmission
separation over at least a day. ( each transmitter will trigger from a
different leg of a decade counter) . the transmitters will all plug in to a
base station at the beginning of the day to reset the clocks to sync them)

I am restricted with space as I want it to fit in a keyfob transmitter, and
am restricted by power - the transmitter works off an AA-style 12V cell, but
I don't mind the clock circuit running off a coin cell.

Philips do a range of watch chips: eg
http://www.semiconductors.philips.com/acrobat/datasheets/PCA16XX_3.pdf
but they output 1Hz (0.5 Hz if you only count the +ve parts of the cycle)
and are a pain to program.
I can't find these for sale anywhere either (UK), as I was thinking of using
a higher freq xtal to speed it up if I could get hold of one. (if this would
work)

Has anyone got any sources of low power chips for precise timing like the
philips chip?. it would be great if they could work from 12V too. they need
to be resettable so I can sync them
. In a perfect world they would interface with the decade counter too but I
can sort that out.
If all else fails, does anyone know of a source of these philips chips
(PCA2002T/1 looks good)

I would be grateful of any feedback!

many thanks

Steve
Manchester, UK
spam@stevecowley.com (change_spam@_to_electronics@ to reply)

GPS chips have a one pulse per second output. You could just double this
with some simple RC mechanism. Then you wouldn't need the synchronization.
Let the DoD keep them synchronized for you. ;-)

But I have a couple of other ideas.

1) Make the fobs transponders, as others have suggested. Then the central
unit could interrogate them, thus providing a synchronization event. Each
fob could have a different, or random delay after receiving this
interrogation/synchronization message, and could then respond. If an
expected response does not come, the central unit knows someone is MIA.
This could provide a much shorter update interval than the 5 seconds you
are designing to.

2) Instead of fobs, use some kind of RF ID. Every so often, the central
unit enumerates all the RFID devices in the vecinity, and if its inventory
is incomplete, it triggers the alarm.

By the way, as far as water sensing goes, keep in mind that people on
small boats in the ocean often get wet (I mean, soaked) without being in
danger, particularly if they are working. If there are steep seas or
strong winds, waves may even break over the boat. At times like that
everyone will be exhausted, and the last thing they need is a false alarm.
I would probably stick to "out of range" and "manual switch" only as cause
for alarm. But hey, that's just me.

--Mac

 

[DarkMatter]

On Fri, 20 Feb 2004 19:20:07 -0000, "Steve C" &lt;spam@stevecowley.com&gt;
Gave us:

To prevent the transmitters transmitting over the top of each other I wish
them to each transmit 0.5 seconds apart and staggered. To do this I need an
accurate(less than 1s per day or better) 2hz clock signal so that (once I
have sync'd each of the transmitters) they will maintain their transmission
separation over at least a day.

Bad choice. Better to go at a high frequency, and count huge
numbers of cycles that have passed.

Best thing would be to use an RTC chip or module, then, each device
could be programmed to send status signals at specific intervals in
each minute. Then it relies on the accuracy of a highly accurate
crystal and the initial setpoint at startup. Ten units is one at the
minute mark, and one every six seconds. If they are all staggered,
one could intersperse quite an array, and still get individualized
status reports.

We make a 2.5 and a 5Ghz wireless mike that also has data send, and
receive capabilities. You could incorporate our product and get
individually keyed, encrypted transmissions. Then, even though
overboard, your "rescueee" would still have voice send or beacon send
ability up to 1000 feet from the boat.

Not only do you get a status, you get a "Hey! I am over here!"
beacon that you could home on.

I have a feeling that your current design direction is doomed.

 

[DarkMatter]

On 20 Feb 2004 21:54:41 GMT, et472@FreeNet.Carleton.CA (Michael Black)
Gave us:

So is this a design question, or a basic question? It can't
be hard to decide which, and post to the appropriate newsgroup.

Jeez... as if that even matters. Be less anal.

 

[onestone]

A simpler and cheaper method, that allows you to get rid of the crystal
can use simple sequencing. A single chip transceiver is about the same
cost as a transmitter these days, and it adds useful functionality. Each
module is numbered, and that number defines its sequence, all
transceivers hear all others. When # 1 sends and completes #2 then
sends. If # 2 hasn't sent by the end of the Tx slot then #3 is free to
continue, # 2 must now wait until the end of 'session' when there are
free slot times available. If the free slot times are not used the unit
may be interrogated actively, beacons lit etc.

Al

Steve C wrote:

Dear all,
I am looking for a way of producing a 2Hz square wave signal (or just 2hz
pulses of any amplitude really) in a very small package powered from a 2.1V
coin cell lithium battery or 12V, with ~1ppm variation. drift rather than
precision is important (ie it doesn't have to be exactly 2Hz, as long as it
is consistent)

why?:
I am building a man-overboard sensor for a small boat. each of 10 people
carries a small keyfob transmitter, which transmits every 5 seconds to reset
a watchdog timer. Water contact, out of range or a switch will stop
transmission and trigger an alarm.

To prevent the transmitters transmitting over the top of each other I wish
them to each transmit 0.5 seconds apart and staggered. To do this I need an
accurate(less than 1s per day or better) 2hz clock signal so that (once I
have sync'd each of the transmitters) they will maintain their transmission
separation over at least a day. ( each transmitter will trigger from a
different leg of a decade counter) . the transmitters will all plug in to a
base station at the beginning of the day to reset the clocks to sync them)

I am restricted with space as I want it to fit in a keyfob transmitter, and
am restricted by power - the transmitter works off an AA-style 12V cell, but
I don't mind the clock circuit running off a coin cell.

Philips do a range of watch chips: eg
http://www.semiconductors.philips.com/acrobat/datasheets/PCA16XX_3.pdf
but they output 1Hz (0.5 Hz if you only count the +ve parts of the cycle)
and are a pain to program.
I can't find these for sale anywhere either (UK), as I was thinking of using
a higher freq xtal to speed it up if I could get hold of one. (if this would
work)

Has anyone got any sources of low power chips for precise timing like the
philips chip?. it would be great if they could work from 12V too. they need
to be resettable so I can sync them
. In a perfect world they would interface with the decade counter too but I
can sort that out.
If all else fails, does anyone know of a source of these philips chips
(PCA2002T/1 looks good)

I would be grateful of any feedback!

many thanks

Steve
Manchester, UK
spam@stevecowley.com (change_spam@_to_electronics@ to reply)

--
Please remove capitalised letters to reply
My apologies for the inconvenience
Blame it on the morons that spam the net

 

[Michael Black]

DarkMatter (DarkMatter@thebarattheendoftheuniverse.org) writes:

On 20 Feb 2004 21:54:41 GMT, et472@FreeNet.Carleton.CA (Michael Black)
Gave us:

So is this a design question, or a basic question? It can't
be hard to decide which, and post to the appropriate newsgroup.


Jeez... as if that even matters. Be less anal.

No kid, I'm tired of the mess of the hierarchy. If we're all going
to cross-post, or post to whichever newsgroup in the hierarchy that
we feel like, then there was no reason to split sci.electronics up
into the present multiple newsgroups back in 1995.

We've got all kinds of off topic junk in sci.electronics.design not
merely drift but outright junk because people have decided the newsgroup
is a place to hang out, rather than a place for the specific topic.

We see people asking computer questions, or design questions in the repair
newsgroup, and people asking repair questions in the design newsgroup.
We have people claiming they haven't got any answers when they've asked
in the basics newsgroup, so they decided they'll hang out in the design
newsgroup. We see ads coming in, and few are saying anything against
them, though they clearly do not belong. We see Paul Burridge routinely
cross-post between sci.electronics.design and rec.radio.amateur.homebrew
And it goes on and on.

Cross-posting, in all but a tiny number of cases, is because the poster
is too lazy to figure out which newsgroup the question fits in, or doesn't
care.

Michael

 

[DarkMatter]

On 21 Feb 2004 17:31:45 GMT, et472@FreeNet.Carleton.CA (Michael Black)
Gave us:

DarkMatter (DarkMatter@thebarattheendoftheuniverse.org) writes:
On 20 Feb 2004 21:54:41 GMT, et472@FreeNet.Carleton.CA (Michael Black)
Gave us:

So is this a design question, or a basic question? It can't
be hard to decide which, and post to the appropriate newsgroup.


Jeez... as if that even matters. Be less anal.

No kid, I'm tired of the mess of the hierarchy. If we're all going
to cross-post, or post to whichever newsgroup in the hierarchy that
we feel like, then there was no reason to split sci.electronics up
into the present multiple newsgroups back in 1995.

Ten years has passed. Usenet has changed a lot since then. We have
twits that think that top posting is OK, twits that think HTML is ok
and twits like you that think that every post needs to be scrutinized
like some lame drill sergeant that didn't get any last night.

We've got all kinds of off topic junk in sci.electronics.design not
merely drift but outright junk because people have decided the newsgroup
is a place to hang out, rather than a place for the specific topic.

My god, you don't even know how to use your news client correctly.

Bone up, Chucko.

We see people asking computer questions, or design questions in the repair
newsgroup, and people asking repair questions in the design newsgroup.

Ok. Chastising them will get you nowhere. You and I both know that
Usenet is like mardi gras. If you don't believe that, you are in for
yet more shocking news. Hahaha... news... Usenet... hahaha... funny.

We have people claiming they haven't got any answers when they've asked
in the basics newsgroup, so they decided they'll hang out in the design
newsgroup.

Jeez... anal isn't even the word here.

We see ads coming in, and few are saying anything against
them, though they clearly do not belong.

You do not "say anything against them", you SEND a complaint to the
sender's ISP. Got clue?

We see Paul Burridge routinely
cross-post between sci.electronics.design and rec.radio.amateur.homebrew
And it goes on and on.

He has mental issues with conventions and rules. Are you saying
that you do not? Netcop wanna be needs to stomp feet less.

Cross-posting, in all but a tiny number of cases, is because the poster
is too lazy to figure out which newsgroup the question fits in, or doesn't
care.

No. It is more likely a common practice because the poster(s)
see(s) it done in everyday reading of ANY given group.

It is viewed much more likely as "common practice" than anything
about "the rules and standards for posting in Usenet", because 95% of
Usenet posters treat the forum as a chat board or e-mail client,
instead of archived historical data. They have never read anything
which relate to actual proper use of this forum.

The calls for another "Got clue?"

Got clue?