Hi Everyone,
I'm using an LM339 window comparator to send signals to a
PIC16F84-04. I did most of my testing during daylight hours and everything
worked well. But last night I realise that when either the florescence lamps
or the washing machine was turned ON, it switched the window comparator ON
thereby causing the Pic to false trigger.
At first I thought this interference was passing through the
rectifier cct but I've since disconnected this and resort to a battery
supply but the problem still exists.
Does any one have any suggestions on how to solve this problem? I'd
be grateful.
If you think it is something in area of where you are
working in this, remove the sources one by one (if possible), or since
you did use a battery for power, take the device away from the suspected
noise source. It might not be either one of the suspected sources.
> Hi Everyone,
> I'm using an LM339 window comparator to send signals to a
> PIC16F84-04. I did most of my testing during daylight hours and everything
> worked well. But last night I realise that when either the florescence lamps
> or the washing machine was turned ON, it switched the window comparator ON
> thereby causing the Pic to false trigger.
> At first I thought this interference was passing through the
> rectifier cct but I've since disconnected this and resort to a battery
> supply but the problem still exists.
I've been pondering about this message for a while. Fluorescents are
notorious noise machines, but a washing machine ?
So, here's my 2 bits:
1. A washing machine draws a lot of power, especially with the heater on.
This opens the way for ground current faults and magnetic noise coupling.
Do you have a shared ground between the project and something else ? Do
you have a closed ground or other trace loop on the board ? Is it close to
electrical wiring or electrical machine chassis (Ferrous, magnetic) ?
Break any loops that there may be. If the loop has to be there break it
with a 10 ohm resistor or such.
2. In the evening, HF propagation is better, and hams get on the air. The
339 is fast enough to pick the lower bands up. Maybe some of the effects
cumulate to upset your project. Sprinkle some small decoupling capacitors
on the inputs to the board (100-330 pF depending on what you do).
>2. In the evening, HF propagation is better, and hams get on the air. The
>339 is fast enough to pick the lower bands up. Maybe some of the effects
>cumulate to upset your project. Sprinkle some small decoupling capacitors
>on the inputs to the board (100-330 pF depending on what you do).
This last is extremely unlikely, due to the inverse square law.
If one of your immediate neighbors has an antenna farm, then maybe, but even
the most powerful stations allowed by law soon damp out into the microvolts,
assuming a large antenna.
Locally produced spikes are a much more likely culprit.
Does your circuit have any positive feedback to set a minimum amount above
threshold?
> >2. In the evening, HF propagation is better, and hams get on the air. The
> >339 is fast enough to pick the lower bands up. Maybe some of the effects
> >cumulate to upset your project. Sprinkle some small decoupling capacitors
> >on the inputs to the board (100-330 pF depending on what you do).
>
>
> This last is extremely unlikely, due to the inverse square law.
> If one of your immediate neighbors has an antenna farm, then maybe, but even
> the most powerful stations allowed by law soon damp out into the microvolts,
> assuming a large antenna.
>
> Locally produced spikes are a much more likely culprit.
Probably, but do not under-estimate the 339 ;) It CAN and DOES react to
microvolt signals in certain circuits. Happens to me all the time (I use
the 339 a lot in interfaces and logic level converters/adpaters). I am
pretty certain that a reasonable AM radio with a D class audio amplifier
can be built with a 339 ;) In fact, I've seen a schematic somewhere that
does just this. Now, add a long wire to a sensor or two, and a beacon or
ham Tx in the 100 Watt range not more than 30-100 meters away and you can
play Marconi all over again <g> (assuming that the wire is tuned right
<vbg). Of course spikes do it all the time but they are short, and I know
of no washing machine that makes spikes ?!
>Probably, but do not under-estimate the 339 ;) It CAN and DOES react to
>microvolt signals in certain circuits. Happens to me all the time (I use
>the 339 a lot in interfaces and logic level converters/adpaters). I am
>pretty certain that a reasonable AM radio with a D class audio amplifier
>can be built with a 339 ;) In fact, I've seen a schematic somewhere that
>does just this. Now, add a long wire to a sensor or two, and a beacon or
>ham Tx in the 100 Watt range not more than 30-100 meters away and you can
>play Marconi all over again <g> (assuming that the wire is tuned right
><vbg).
That, I'll agree with... I've done a stereo amp consisting of an HC74 and a
pair of HC14's (speaker drivers)
It plays nicely. 3.5 Mhz clock.
> Of course spikes do it all the time but they are short, and I know of no
washing machine that makes spikes ?!
At 09:34 AM 4/09/98 -0300, you wrote:
>Hi Everyone,
> I'm using an LM339 window comparator to send signals to a
>PIC16F84-04. I did most of my testing during daylight hours and everything
>worked well. But last night I realise that when either the florescence lamps
>or the washing machine was turned ON, it switched the window comparator ON
>thereby causing the Pic to false trigger.
> At first I thought this interference was passing through the
>rectifier cct but I've since disconnected this and resort to a battery
>supply but the problem still exists.
>
> Does any one have any suggestions on how to solve this problem? I'd
>be grateful.
>
>
This may be a bit strainge, but the 339 comp, has no external pull ups on
the output, so what you may be seeing is floating inputs to the PIC. If this
is not so, then the problem may be that the input circuits to the 339 are at
a too high impedance, and will need to be biased harder.
> On Fri, 4 Sep 1998, Rawle Watson wrote:
>
> > Hi Everyone,
> > I'm using an LM339 window comparator to send signals to a
> > PIC16F84-04. I did most of my testing during daylight hours and everything
> > worked well. But last night I realise that when either the florescence lamps
> > or the washing machine was turned ON, it switched the window comparator ON
> > thereby causing the Pic to false trigger.
> > At first I thought this interference was passing through the
> > rectifier cct but I've since disconnected this and resort to a battery
> > supply but the problem still exists.
>
> It could be your washing machine if it's a Fisher and Paykel... I've heard of
> people having a really bad time trying to receive sw radio because there
> neighbour has owned the above mentioned machine. The explanation was that the
> clock for the micro in the machine was running at 13.5 mhz and gave off a larg
er
> than normal signal which apparently flooded the receivers.
> >2. In the evening, HF propagation is better, and hams get on the air. The
> >339 is fast enough to pick the lower bands up. Maybe some of the effects
> >cumulate to upset your project. Sprinkle some small decoupling capacitors
> >on the inputs to the board (100-330 pF depending on what you do).
>
>
> This last is extremely unlikely, due to the inverse square law.
> If one of your immediate neighbors has an antenna farm, then maybe, but even
> the most powerful stations allowed by law soon damp out into the microvolts,
> assuming a large antenna.
hehehe, I've been thinking over this one. I had a friend in a small town
that happened to have a 100 kW local AM station installed on a field just
outside the town. Every phone, tape recorder, record player and in fact,
anything that had a speaker and some rectifier in it, played the station's
music. No, the place was not in sight of the antenna. Perhaps a freak
local receiving area. So the inverse square law is correct, as far as the
physics are concerned, but the physics stop being pure when they exit the
lab and meet Murphy... The inverse square law is excellent to put you in
the ballpark so to say, but for a reality check, how about a wave strength
meter at the location in question ;)
Same topic on Stamp list recently. This was my comment:
My old shop had a house next door - The guy was running a
couple of kw (my estimate) to a big vertical on a tower - His
specialty was conducting screaming matches with members of ethnic
groups of which he disapproved - The most vulgar stuff imaginable.
I could hear him on the phone, radios, tvs, computer, fillings. etc.
His signal was quite visible on my scope and DVM ...
I figured if my designs hacked this asshole then they were probably
ok...
In case this is'nt clear, we're talking cb, NOT ham.
>
> On Sun, 6 Sep 1998, David VanHorn wrote:
>
> > >2. In the evening, HF propagation is better, and hams get on the air. The
> > >339 is fast enough to pick the lower bands up. Maybe some of the effects
> > >cumulate to upset your project. Sprinkle some small decoupling capacitors
> > >on the inputs to the board (100-330 pF depending on what you do).
> >
> >
> > This last is extremely unlikely, due to the inverse square law.
> > If one of your immediate neighbors has an antenna farm, then maybe, but even
> > the most powerful stations allowed by law soon damp out into the microvolts,
> > assuming a large antenna.
>
> hehehe, I've been thinking over this one. I had a friend in a small town
> that happened to have a 100 kW local AM station installed on a field just
> outside the town. Every phone, tape recorder, record player and in fact,
> anything that had a speaker and some rectifier in it, played the station's
> music. No, the place was not in sight of the antenna. Perhaps a freak
> local receiving area. So the inverse square law is correct, as far as the
> physics are concerned, but the physics stop being pure when they exit the
> lab and meet Murphy... The inverse square law is excellent to put you in
> the ballpark so to say, but for a reality check, how about a wave strength
> meter at the location in question ;)
>
> Peter
>hehehe, I've been thinking over this one. I had a friend in a small town
>that happened to have a 100 kW local AM station installed on a field just
>outside the town. Every phone, tape recorder, record player and in fact,
>anything that had a speaker and some rectifier in it, played the station's
>music. No, the place was not in sight of the antenna. Perhaps a freak
>local receiving area. So the inverse square law is correct, as far as the
>physics are concerned, but the physics stop being pure when they exit the
>lab and meet Murphy... The inverse square law is excellent to put you in
>the ballpark so to say, but for a reality check, how about a wave strength
>meter at the location in question ;)
>
>Peter
Exactly my point. You notice you don't hear any ham stations.... 1500W vs
100000W..
I was debating the likelyhood of interference sources. Rather than dig for
the exotic, I think he would best spend his time looking for sources that
are much more common.
For exotic, how about boat radar interfering with a phone system... Seen it,
found it, fixed it. But it wasn't my first guess. Since I've only seen it
happen once in 20 years, should I always jump to that as the first try?
-----Original Message-----
From: David VanHorn <spam_OUTdvanhornTakeThisOuTCEDAR.NET>
>
>For exotic, how about boat radar interfering with a phone system...
Seen it,
>found it, fixed it. But it wasn't my first guess. Since I've only
seen it
>happen once in 20 years, should I always jump to that as the first
try?
>
Best version I've seen of this was when a foreign warship entered our
capital cities harbor (Wellington, New Zealand) on a show the flag
tour and was docked against the wharf near the city's main telephone
exchange.
They were told that radar was not to be used in the harbor. The
telephone system suddenly developed a strong interference pulse on
many circuits and you could look out the window from offices further
up the city and see how the interference exactly coincided with the
rotation of the radar scanner on the warship ;-).
Needless to say this was stopped v v quickly.
Shows how easily our systems will die under EMP conditions if they
ever occur.
We have a radio station here in South Oklahoma City - a lot of shortwave
and HAM people have heard of it - KOMA. They are an oldies station.
Anyway, they are outputting at the FCC's maximum allowed output for a
commercial AM station. To further muck up the works, they have a
three-antenna phased array with cross-beam couplers. Kind of like one of
the old CB antennas - the "Starcaster" - it had a big target-shaped thing
on the end and an aluminum reflector plate at the back. Mean antenna, that
was.
Anyway, this AM station comes in on a lot of toasters down there (about 2
miles from my house) - yet I don't get a glimmer. I knew a guy lived in an
apartment complex in LOS of the antenna array. He couldn't have anything
running with the remote possibility of resonating - no crystal-oscillator
based micro-electronics. It was ugly. At night, they used to crank their
power a little bit. Apparently they could alter the phase of the signal to
the antenna(s) and "steer" the output a bit. There are a few recordings
they play of folks up in North Dakota picking them up on the cloud-bounce.
My brother used to pick them up on the ship's comm gear when he was in the
Navy out in the North Atlantic.
The point of this is that the inverse square law is correct. This is a
physical property of electromagnetic radiation. However, atmospheric
effects and local clutter all affect he way an EM wave propagates and
refracts/diffracts/attenuates, etc. You can even get amplifying effects
during the right electrical conditions in the atmosphere. Some well-made
receivers (and some things that aren't even *supposed* to be receivers) can
pick up and amplify signals in the 1/100 mW range fairly easily.
>hehehe, I've been thinking over this one. I had a friend in a small town
>that happened to have a 100 kW local AM station installed on a field just
>outside the town. Every phone, tape recorder, record player and in fact,
>anything that had a speaker and some rectifier in it, played the station's
>music. No, the place was not in sight of the antenna. Perhaps a freak
>local receiving area. So the inverse square law is correct, as far as the
>physics are concerned, but the physics stop being pure when they exit the
>lab and meet Murphy... The inverse square law is excellent to put you in
>the ballpark so to say, but for a reality check, how about a wave strength
>meter at the location in question ;)
>
>Peter
>
>
>-----Original Message-----
>From: David VanHorn <.....dvanhornKILLspam@spam@CEDAR.NET>
>>
>>For exotic, how about boat radar interfering with a phone system...
>Seen it,
>>found it, fixed it. But it wasn't my first guess. Since I've only
>seen it
>>happen once in 20 years, should I always jump to that as the first
>try?
>>
>
>Best version I've seen of this was when a foreign warship entered our
>capital cities harbor (Wellington, New Zealand) on a show the flag
>tour and was docked against the wharf near the city's main telephone
>exchange.
>
>They were told that radar was not to be used in the harbor. The
>telephone system suddenly developed a strong interference pulse on
>many circuits and you could look out the window from offices further
>up the city and see how the interference exactly coincided with the
>rotation of the radar scanner on the warship ;-).
>
Let me guess. It was an American. They have done that in Canada as well.
Some of those air
search radars are quite powerful not to mention dangerous. I have heard
rumours of cooking birds
in flight at 500 yards. Think what that might do to your body.
>Needless to say this was stopped v v quickly.
>Shows how easily our systems will die under EMP conditions if they
>ever occur.
>
>
>At 09:53 AM 09/09/98 +1200, you wrote:
>>-----Original Message-----
>>From: David VanHorn <dvanhornKILLspamCEDAR.NET>
>>>
>>>For exotic, how about boat radar interfering with a phone system...
>>Seen it,
>>>found it, fixed it. But it wasn't my first guess. Since I've only
>>seen it
>>>happen once in 20 years, should I always jump to that as the first
>>try?
>>>
>>
>>Best version I've seen of this was when a foreign warship entered our
>>capital cities harbor (Wellington, New Zealand) on a show the flag
>>tour and was docked against the wharf near the city's main telephone
>>exchange.
>>
>>They were told that radar was not to be used in the harbor. The
>>telephone system suddenly developed a strong interference pulse on
>>many circuits and you could look out the window from offices further
>>up the city and see how the interference exactly coincided with the
>>rotation of the radar scanner on the warship ;-).
>>
>
> Let me guess. It was an American. They have done that in Canada as well.
>Some of those air
>search radars are quite powerful not to mention dangerous. I have heard
>rumours of cooking birds
>in flight at 500 yards. Think what that might do to your body.
>
>
That's way they co ordain off the area when the antennae is on the ground. I
have heard of a poor soul whom walked through one, and well, microwave
human. As for the power levels, well needless to say that it puts AM and FM
radio stations too shame.
CEDAR.NET>
