1-Wire Weather and the BS2p
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Hi everyone,
I have a BS2p and and three 1-Wire sensors (humidity, temperature and
rain). The BS2p and sensors are about 30 feet from each other on cat 5E
cable. Just to get them to work I had to lower the pull-up resistor to 500
ohms and ground 1 unused pair in the cat 5. I still get a lot of bad data at
times. I plan to add the weather station from AAG in the near future. Anyone
have any suggestions on how to clean up the data. Using a 1k pull up it
wouldn't work at all.
Thanks in advance,
Bill
I have a BS2p and and three 1-Wire sensors (humidity, temperature and
rain). The BS2p and sensors are about 30 feet from each other on cat 5E
cable. Just to get them to work I had to lower the pull-up resistor to 500
ohms and ground 1 unused pair in the cat 5. I still get a lot of bad data at
times. I plan to add the weather station from AAG in the near future. Anyone
have any suggestions on how to clean up the data. Using a 1k pull up it
wouldn't work at all.
Thanks in advance,
Bill
Comments
Had the exact problem when doing a network of 16 DS1820's on 300' of cable.
A lot has to do with the way you tap off the cat 5 backbone cable and the
reflections that are caused on the OWB. If your tap is greated than a few
feet reflections cause unreliable results. One cure is something I
discovered in the mounds of tech data and that was installing a 100 ohme in
series with the data lead only at the stub connection to the backbone. It
is detailed on Tech Note from Dallas. I believe the title was OWN
reliability (Yea Sure) . When you first read about the OWB it sounds great
but after you get more than a few feet away and have nultiple sensors
everything goes to pot. It took me months to overcome this problem and their
tech help never returned my messages. Consequently when I found the problem
I will remember the fix forever.
Eric
Good Luck
Original Message
From: "Bill Cramer" <billcramer@a...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, April 01, 2003 8:15 PM
Subject: [noparse][[/noparse]basicstamps] 1-Wire Weather and the BS2p
> Hi everyone,
>
> I have a BS2p and and three 1-Wire sensors (humidity, temperature and
> rain). The BS2p and sensors are about 30 feet from each other on cat 5E
> cable. Just to get them to work I had to lower the pull-up resistor to 500
> ohms and ground 1 unused pair in the cat 5. I still get a lot of bad data
at
> times. I plan to add the weather station from AAG in the near future.
Anyone
> have any suggestions on how to clean up the data. Using a 1k pull up it
> wouldn't work at all.
>
> Thanks in advance,
> Bill
>
>
> To UNSUBSCRIBE, just send mail to:
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>
>
people already did!
Seriously though, you haven't told us much about your circuit so I'll toss
out a few ideas, you may already know/have done them.
First, is the cat-5 shielded? If so, have you grounded the stamp end of the
shield? (Dont connect the far end to ground). This will help keep EMFs from
interfering with the data too much.
Second, are the three sensors sharing a single cable? If so, they could be
inducing currents in each other and messing up the data (shot in the dark)
What do you have the circuit laid out on? Carrier board, breadboard, wire
wrap, PCB?
My 'lectronic Newb site http://members.shaw.ca/pmeloy/
Original Message
From: "Bill Cramer" <billcramer@a...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, April 01, 2003 5:15 PM
Subject: [noparse][[/noparse]basicstamps] 1-Wire Weather and the BS2p
> Hi everyone,
>
> I have a BS2p and and three 1-Wire sensors (humidity, temperature and
> rain). The BS2p and sensors are about 30 feet from each other on cat 5E
> cable. Just to get them to work I had to lower the pull-up resistor to 500
> ohms and ground 1 unused pair in the cat 5. I still get a lot of bad data
at
> times. I plan to add the weather station from AAG in the near future.
Anyone
> have any suggestions on how to clean up the data. Using a 1k pull up it
> wouldn't work at all.
>
> Thanks in advance,
> Bill
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
Thanks Pat and Eric for the response.
To answer Pat's questions, no the cat 5 is not shielded, and the sensors are
from Jim Jennings (www.jjware.com). One is a temp/humidity sensor and the other
is a general purpose counter module. The cat 5 runs from the Stamp about 30 feet
to the temp/humidity module. Then a 2 foot cat 5 jumper connects to the counter
which is connected to my rain guage. As I told you the pull-up is at 500 ohms
and one unused pair of the cat 5 is grounded at the Stamp.
[noparse][[/noparse]Non-text portions of this message have been removed]
Do you have filter caps sprinkled on the board?
Jonathan
www.madlabs.info
Original Message
From: "Bill Cramer" <billcramer@a...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, April 02, 2003 4:48 AM
Subject: [noparse][[/noparse]basicstamps] 1-wire weather and the BS2p
> Good morning,
>
> Thanks Pat and Eric for the response.
> To answer Pat's questions, no the cat 5 is not shielded, and the sensors
are from Jim Jennings (www.jjware.com). One is a temp/humidity sensor and
the other is a general purpose counter module. The cat 5 runs from the Stamp
about 30 feet to the temp/humidity module. Then a 2 foot cat 5 jumper
connects to the counter which is connected to my rain guage. As I told you
the pull-up is at 500 ohms and one unused pair of the cat 5 is grounded at
the Stamp.
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
>
dealing with Analog sensors with currents down in the femto-amperes (berry
berry small!) so signal conditioning and noise-harm reduction is what I've
been concentrating on for the last while. Haven't really thought about how
these things could affect digital signals so keep that in mind.
The biggies:
Seperate cables for the sensors may help, though since you're only talking
to one sensor at a time it might be useless - who cares if sensor two has
induced currents if you aren't talking to it at the time?
Shield the cable - Probably a good idea. RS232 cables off a computer have a
practical length limit around 25 feet (depends on lot on the environment).
Any longer and you need "booster" boxes. Shielding keeps RF from messing up
signals (very big effect on my femto-ampere sensor, digital I dunno). Just
remember to connect the shield ground at the MCU end and leave the sensor
end un-connected (If using an ADC, make sure the shield is grounded at the
same point your REF- is connected). Sometimes you want to use a powered
shield, +5v or whatever. Haven't figured out when that is required yet.
Still learning!
Decouple the power at your chips - Whenever a chip does something it draws
power. When its not doing anything it draws very little power. The
transition between the two states causes a power pulse, this pulse causes EM
emissions which can induce noise into the rest of your circuit. The longer
the power trace/wire, the bigger the transmitting antenna it becomes. Place
a 0.1 or 1.0uF cap right by each chip's power pin. The power supply will
charge the cap and that section of the wiring won't have the pulses. When
the chip draws more power, the Cap will supply the current - since it is
nice and close to the chip your transmitting antenna is nice and small.
Place a low-pass filter on the signal line to cancel out 60hz noise (or 50hz
if you're in Europe/Asia). For 60hz you can use a 0.1uF tantalum cap and 80
ohm resistor in series to ground. There are also high-pass and inductance
filters which I haven't researched yet.
Use a single ground point - The sensors and chip should be hooked to ground
at the same point. Its possible to get different potentials if the grounds
are far apart. The Pic needs (I think) 1.2V or higher to consider the pin
"high". If you have a voltage drop of 3.7v and the grounds are 0.2v apart,
you'd only get 1.1v and the stamp wouldn't acknowledge the high state.
The smaller resistor isn't all that unusual. 1k-10k pullups are common but
those assume the transmitter is on the same PCB - only a few inches away.
If worst comes to worse, you can also add a 1 x gain op-amp before the
stamp. Some op-amps have a built in frequency rejection and they can clean
up square waves real nice. If your signal voltages come in too low you can
add some gain to get it into the right range as well (Only read about this a
couple of days ago).
Thats all I know so far.
My 'lectronic Newb site http://members.shaw.ca/pmeloy/
Original Message
From: "Bill Cramer" <billcramer@a...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, April 02, 2003 4:48 AM
Subject: [noparse][[/noparse]basicstamps] 1-wire weather and the BS2p
> Good morning,
>
> Thanks Pat and Eric for the response.
> To answer Pat's questions, no the cat 5 is not shielded, and the sensors
are from Jim Jennings (www.jjware.com). One is a temp/humidity sensor and
the other is a general purpose counter module. The cat 5 runs from the Stamp
about 30 feet to the temp/humidity module. Then a 2 foot cat 5 jumper
connects to the counter which is connected to my rain guage. As I told you
the pull-up is at 500 ohms and one unused pair of the cat 5 is grounded at
the Stamp.
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
with the power supply, In other words, power goes directly to the chips and
the cap goes from the power line to ground. You probably know that but, just
in case.
My 'lectronic Newb site http://members.shaw.ca/pmeloy/
Original Message
From: "Pat M" <pmeloy@s...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, April 02, 2003 3:10 PM
Subject: Re: [noparse][[/noparse]basicstamps] 1-wire weather and the BS2p
For 30 feet on a single wire, make sure that a good
ground reference is present to all devices. Also
follow the advice about appropriate amounts of filter
capacitors for all devices to ensure the supply
voltage is DC.
Are the drive levels from the sensors sufficient to
travel the entire cable distance from the BS2P and to
all the sensors? Even though only one device is
talking on the line, the signal still has to travel to
each sensor just the same; thus adding further wire
length between a sensor to the Stamp. I would consider
having each sensor on a separate line. This will be
more of an issue at 500 feet as each sensor creates a
load on the wire. That is why you are having to change
your termination resistor value from the reference
design.
Having _shielded_ Cat 5 cable is not a necessity, but
why not take advantage of the twisted pair
characteristic of the Cat 5 cable (noise immunity) and
use differential transcievers such as 75176s for
RS-485 or similar for RS-422? RS-485 and RS-422 are
rated to about 4000 feet between nodes for slow speed
communications. RS-485 can also be used for multipoint
wiring applications. Wiring Tip and Ring leads of each
pair is not recommended as this does something
different (not necessarily nice) for the signalling
you are trying to put through on the cable.
In your application, where are both devices going to
be located? If they are going to be both mounted on a
mast, why not located the Stamp out there also. This
would keep the 1-wire links short, and longer haul
techinques such as RS-422 or RS-485 drivers can be
employed to bring the data down to a host PC. Use
dedicated I/O pins for each device to cut down on
loading or the I/O pins. Power for all devices can be
put down 2 of the pairs in the Cat 5 group - 1 for
+%VDC and the other for return (ground). To be in
spec, the +5VDC should be higher to compensate for
Ohm's Law losses in the cable run and the actual
devices under power. This technique is similar to what
is being consider for the PoE (Power over Ethernet)
standard.
kevin / kc6pob
--- Bill Cramer <billcramer@a...> wrote:
> Hi everyone,
>
> I have a BS2p and and three 1-Wire sensors
> (humidity, temperature and
> rain). The BS2p and sensors are about 30 feet from
> each other on cat 5E
> cable. Just to get them to work I had to lower the
> pull-up resistor to 500
> ohms and ground 1 unused pair in the cat 5. I still
> get a lot of bad data at
> times. I plan to add the weather station from AAG in
> the near future. Anyone
> have any suggestions on how to clean up the data.
> Using a 1k pull up it
> wouldn't work at all.
>
> Thanks in advance,
> Bill
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed.
> Text in the Subject and Body of the message will be
> ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
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If you or anyone else has BS2P code for running the (newish) AAG Version
3.0 One Wire weather station, please let me know. The old article in
Nuts & Volts magazine was not for V3.0.
Thanks,
Chris
<<>>
Bill Cramer <billcramer@a...> wrote:
> Hi everyone,
>
> I have a BS2p and and three 1-Wire sensors
> (humidity, temperature and
> rain). The BS2p and sensors are about 30 feet from
> each other on cat 5E
> cable. Just to get them to work I had to lower the
> pull-up resistor to 500
> ohms and ground 1 unused pair in the cat 5. I still
> get a lot of bad data at
> times. I plan to add the weather station from AAG in
> the near future. Anyone
> have any suggestions on how to clean up the data.
> Using a 1k pull up it
> wouldn't work at all.
>
> Thanks in advance,
> Bill
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Original Message
From: <cdundorf@j...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, April 03, 2003 9:10 PM
Subject: [noparse][[/noparse]basicstamps] Re: 1-Wire Weather and the BS2p
> Hi Bill,
>
> If you or anyone else has BS2P code for running the (newish) AAG Version
> 3.0 One Wire weather station, please let me know. The old article in
> Nuts & Volts magazine was not for V3.0.
Chris
I haven't purchased the weather station from AAG yet since I'm having a lot
of trouble with my temperature/humidity board and rain guage counter board
and 1-wire bus. However the software I downloaded from
http://homepage.mac.com/tbitson/weather/index.html should work.It addersses
the same 1-wire chips as is in the V3.0 weather station.