White Noise Source

[George Herold]

On Feb 18, 3:31 am, Ben / SM0KBW <k...@allt2.se> wrote:

George Herold skrev 2012-02-11 00:16:





On Feb 10, 4:16 pm, Chiron<chiron...@gmail.com>  wrote:
On Fri, 10 Feb 2012 19:22:39 +0000, Jasen Betts wrote:

snip

if linux, this is easy:

cat /dev/urandom>  /dev/audio

(dev/audio is (IIRC) mono 8 bit Ulaw and runs at a fixed sample rate of
about 8000 samples  per second so it's not propper white noise.

for something better try sox or audacity.

That's very close to what I did - cat /dev/urandom>  randomfile.  Then I
imported that as a raw file into audacity, converted it to ogg format.
When I looked at its spectrum, it was suspiciously flat all the way from
zero to 20kHz, where it fell off at>  30 dB per octave.  Just a little
*too* perfect.  I go by the maxim that, if everything goes according to
plan, you've obviously overlooked something.

Anyway, it's a nice, noisy signal, but I'm still going to do the other
one just for fun (amplified diode noise).  As someone pointed out, having
a quick noise source around could be handy for other reasons besides
talking to ghosts.

--
sel>  need help: my first packet to my provider gets lost :-(
netgod>  sel:  dont send the first one, start with #2

With the a 20V zener you don't need any amplifictaion, just a
buffer.
I wrapped this together on the top of a power supply.

     +15
      |
     1 Meg
      |
      +--0.1uF--+---->scope (use x10 probe,
      |         |            not a crappy clip lead.)
      Z        100k
      ^         |
      |        GND
     -15V

I saw a random RC step response with a time constant of ~2us.
With something like a few hundred mV step size (on average)
(Driving home I realized that the ~80pf in the clip lead I used to
connect to the scope was my RC.. so I can't pull any 'real' numbers
out.)
You can try it yourself with a x10 probe and report results.
You should do better than two micro seconds.

  George H.

One trick, at least at RF is to use the Zener breakthrough in a regular
transistor, the base - emitter diode backwards can give a very good
noise source ranging upp to 1GHz and even above.

/Ben - SM0KBW- Hide quoted text -

- Show quoted text -

Thanks Ben, I've heard that, but never tried it.

George H.

 

[Baron]

Phil Hobbs Inscribed thus:

Michael Black wrote:

On Sat, 18 Feb 2012, krw@att.bizzzzzzzzzzzz wrote:

Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources
around? Seems like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't
because of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor. And he mentioned trying
some small signal diodes and having AC hum on the output, until he
realized the hum was coming from the desk lamp that was shining on
the clear-cased diode.

I've seen other mentions of problems because of light. I recall one
article warning about it, but not because of hum, but because the
external light was affecting diodes, and they were biased wrong or
something, or maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have
some
ability to better generate noise at a lower voltage or something.
With a
breadboard, it costs very little to try. If it works, simply paint
the LED, get rid of any external problem.

Michael

LEDs make great current switches--the garden variety ones I used in
Footprints had leakage is down in the femtoamps from ~-5V to +0.5V.
The photosensitivity can be a feature as well as a bug, when you use
it to supply DC bias for a capacitive sensor such as a pyroelectric.
(See http://electrooptical.net/#footprints, especially the paper with
the gory technical details.)

Cheers

Phil Hobbs

Seems most of the photos are missing !

--
Best Regards:
Baron.

 

[Ben / SM0KBW]

George Herold skrev 2012-02-19 17:04:

On Feb 18, 3:31 am, Ben / SM0KBW<k...@allt2.se> wrote:
George Herold skrev 2012-02-11 00:16:





On Feb 10, 4:16 pm, Chiron<chiron...@gmail.com> wrote:
On Fri, 10 Feb 2012 19:22:39 +0000, Jasen Betts wrote:

snip

if linux, this is easy:

cat /dev/urandom> /dev/audio

(dev/audio is (IIRC) mono 8 bit Ulaw and runs at a fixed sample rate of
about 8000 samples per second so it's not propper white noise.

for something better try sox or audacity.

That's very close to what I did - cat /dev/urandom> randomfile. Then I
imported that as a raw file into audacity, converted it to ogg format.
When I looked at its spectrum, it was suspiciously flat all the way from
zero to 20kHz, where it fell off at> 30 dB per octave. Just a little
*too* perfect. I go by the maxim that, if everything goes according to
plan, you've obviously overlooked something.

Anyway, it's a nice, noisy signal, but I'm still going to do the other
one just for fun (amplified diode noise). As someone pointed out, having
a quick noise source around could be handy for other reasons besides
talking to ghosts.

--
sel> need help: my first packet to my provider gets lost :-(
netgod> sel: dont send the first one, start with #2

With the a 20V zener you don't need any amplifictaion, just a
buffer.
I wrapped this together on the top of a power supply.

+15
|
1 Meg
|
+--0.1uF--+---->scope (use x10 probe,
| | not a crappy clip lead.)
Z 100k
^ |
| GND
-15V

I saw a random RC step response with a time constant of ~2us.
With something like a few hundred mV step size (on average)
(Driving home I realized that the ~80pf in the clip lead I used to
connect to the scope was my RC.. so I can't pull any 'real' numbers
out.)
You can try it yourself with a x10 probe and report results.
You should do better than two micro seconds.

George H.

One trick, at least at RF is to use the Zener breakthrough in a regular
transistor, the base - emitter diode backwards can give a very good
noise source ranging upp to 1GHz and even above.

/Ben - SM0KBW- Hide quoted text -

- Show quoted text -

Thanks Ben, I've heard that, but never tried it.

George H.

I've only used that kind of noise source when i'm aligning VHF and UHF
preamps. The zener breakthrough is at around 6V for ordinary
transistors as the 2N2222. You have to test a handful to find the best
noise source

/Ben - SM0KBW

 

[Phil Hobbs]

Baron wrote:

Phil Hobbs Inscribed thus:

Michael Black wrote:

On Sat, 18 Feb 2012, krw@att.bizzzzzzzzzzzz wrote:

Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources
around? Seems like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't
because of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor. And he mentioned trying
some small signal diodes and having AC hum on the output, until he
realized the hum was coming from the desk lamp that was shining on
the clear-cased diode.

I've seen other mentions of problems because of light. I recall one
article warning about it, but not because of hum, but because the
external light was affecting diodes, and they were biased wrong or
something, or maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have
some
ability to better generate noise at a lower voltage or something.
With a
breadboard, it costs very little to try. If it works, simply paint
the LED, get rid of any external problem.

Michael

LEDs make great current switches--the garden variety ones I used in
Footprints had leakage is down in the femtoamps from ~-5V to +0.5V.
The photosensitivity can be a feature as well as a bug, when you use
it to supply DC bias for a capacitive sensor such as a pyroelectric.
(See http://electrooptical.net/#footprints, especially the paper with
the gory technical details.)

Cheers

Phil Hobbs

Seems most of the photos are missing !

--
Best Regards:
Baron.

Right! Thanks. Fixed now.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

 

[Baron]

Phil Hobbs Inscribed thus:

Baron wrote:

LEDs make great current switches--the garden variety ones I used in
Footprints had leakage is down in the femtoamps from ~-5V to +0.5V.
The photosensitivity can be a feature as well as a bug, when you
use it to supply DC bias for a capacitive sensor such as a
pyroelectric. (See http://electrooptical.net/#footprints,
especially the paper with the gory technical details.)

Cheers

Phil Hobbs

Seems most of the photos are missing !

--
Best Regards:
Baron.

Right! Thanks. Fixed now.

Cheers

Phil Hobbs

Looks fine now. Thanks.

--
Best Regards:
Baron.

 

[Michael A. Terrell]

George Herold wrote:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around? Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor. And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light. I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something. With a
breadboard, it costs very little to try. If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was. (I'll have to do some testing, when I have
time.)
I was tweaking the gain of my zener noise source and turned on the
overhead lamp to get some more light for soldering. The noise dropped
by a factor of ten or more.... and this is with black electrical tape
wrapped around the zeners! Putting my hand over the zeners to shade
them... noise went back up.

I've perhaps made an anvalanche photodiode out of my zener?

It's well known that black vinyl tape is translucent to some light.


--
You can't have a sense of humor, if you have no sense.

 

[Phil Hobbs]

"Michael A. Terrell" wrote:

George Herold wrote:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around? Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor. And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light. I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something. With a
breadboard, it costs very little to try. If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was. (I'll have to do some testing, when I have
time.)
I was tweaking the gain of my zener noise source and turned on the
overhead lamp to get some more light for soldering. The noise dropped
by a factor of ten or more.... and this is with black electrical tape
wrapped around the zeners! Putting my hand over the zeners to shade
them... noise went back up.

I've perhaps made an anvalanche photodiode out of my zener?

It's well known that black vinyl tape is translucent to some light.

Yup. Many black-looking things are coloured with organic dyes, which
become transparent in the near IR. Silicon doesn't really cut off till
about 1100 nm, so there's frequently a detectable leak.

Novolac epoxy (used for chip packages) is opaque at all wavelengths from
the mid-IR to soft X-rays, so it's not an issue with plastic-packaged
chips.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

 

[George Herold]

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:

On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around?  Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor.  And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light.  I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something.  With a
breadboard, it costs very little to try.  If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was. (I'll have to do some testing, when I have
time.)
I was tweaking the gain of my zener noise source and turned on the
overhead lamp to get some more light for soldering. The noise dropped
by a factor of ten or more.... and this is with black electrical tape
wrapped around the zeners! Putting my hand over the zeners to shade
them... noise went back up.

I've perhaps made an anvalanche photodiode out of my zener?

George H.

   Michael

 

[Michael A. Terrell]

Phil Hobbs wrote:

"Michael A. Terrell" wrote:

George Herold wrote:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around? Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor. And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light. I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something. With a
breadboard, it costs very little to try. If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was. (I'll have to do some testing, when I have
time.)
I was tweaking the gain of my zener noise source and turned on the
overhead lamp to get some more light for soldering. The noise dropped
by a factor of ten or more.... and this is with black electrical tape
wrapped around the zeners! Putting my hand over the zeners to shade
them... noise went back up.

I've perhaps made an anvalanche photodiode out of my zener?

It's well known that black vinyl tape is translucent to some light.

Yup. Many black-looking things are coloured with organic dyes, which
become transparent in the near IR. Silicon doesn't really cut off till
about 1100 nm, so there's frequently a detectable leak.

Novolac epoxy (used for chip packages) is opaque at all wavelengths from
the mid-IR to soft X-rays, so it's not an issue with plastic-packaged
chips.

I saw several reels of optical sensors on Ebay this morning, but
probaly nothing of interest to you. I did win a reel of 3,000 UHF
transistors last night, though. I see the seller posted another reel:
"Reel of 3000 UHF 9GHz NPN Transistors Philips/NXP"

http://www.nxp.com/documents/data_sheet/PRF949.pdf

Now, to see what trouble I get into with them. ;-)

--
You can't have a sense of humor, if you have no sense.

 

[JW]

On Mon, 20 Feb 2012 08:46:38 -0800 (PST) George Herold
<gherold@teachspin.com> wrote in Message id:
<db84ada7-d3a7-4673-8067-71e6e02ac4f6@l16g2000vbl.googlegroups.com>:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around?  Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor.  And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light.  I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something.  With a
breadboard, it costs very little to try.  If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was. (I'll have to do some testing, when I have
time.)

Try using some heat-shrink tubing, then pinch the ends closed while still
hot.

 

[Phil Hobbs]

JW wrote:

On Mon, 20 Feb 2012 08:46:38 -0800 (PST) George Herold
gherold@teachspin.com> wrote in Message id:
db84ada7-d3a7-4673-8067-71e6e02ac4f6@l16g2000vbl.googlegroups.com>:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around? Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor. And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light. I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something. With a
breadboard, it costs very little to try. If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was. (I'll have to do some testing, when I have
time.)

Try using some heat-shrink tubing, then pinch the ends closed while still
hot.

Carbon paint is pretty good, e.g. ultraflat black Krylon. It's somewhat
electrically conductive, though, so you have to be careful with it.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

 

On Tue, 21 Feb 2012 09:29:16 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

JW wrote:

On Mon, 20 Feb 2012 08:46:38 -0800 (PST) George Herold
gherold@teachspin.com> wrote in Message id:
db84ada7-d3a7-4673-8067-71e6e02ac4f6@l16g2000vbl.googlegroups.com>:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around? Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor. And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light. I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something. With a
breadboard, it costs very little to try. If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was. (I'll have to do some testing, when I have
time.)

Try using some heat-shrink tubing, then pinch the ends closed while still
hot.

Carbon paint is pretty good, e.g. ultraflat black Krylon. It's somewhat
electrically conductive, though, so you have to be careful with it.

Cheers

Phil Hobbs
So use black paint for white noise?

Eric

 

[George Herold]

On Feb 20, 12:22 pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:

"Michael A. Terrell" wrote:

George Herold wrote:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around?  Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor.  And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light.  I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something.  With a
breadboard, it costs very little to try.  If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was.  (I'll have to do some testing, when I have
time.)
I was tweaking the gain of my zener noise source and turned on the
overhead lamp to get some more light for soldering.  The noise dropped
by a factor of ten or more.... and this is with black electrical tape
wrapped around the zeners!  Putting my hand over the zeners to shade
them... noise went back up.

I've perhaps made an anvalanche photodiode out of my zener?

   It's well known that black vinyl tape is translucent to some light.

Yup.  Many black-looking things are coloured with organic dyes, which
become transparent in the near IR.  Silicon doesn't really cut off till
about 1100 nm, so there's frequently a detectable leak.

Novolac epoxy (used for chip packages) is opaque at all wavelengths from
the mid-IR to soft X-rays, so it's not an issue with plastic-packaged
chips.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -

Thanks Phil, Time to order some more parts.
Say can you buy Novolac epoxy?
(for less than a bottle of good Scotch.)

I figured it might be something out past ~800nm. I've mostly looked
at how the tape blocks the Rb D line's (780 and 795 nm)

I've got a bit of time today and will do a few measurments. I've got
this old Jarrel Ash spectrometer and PAR 1205 multichannel analyzer.
(I'm not sure what the detector is...)

George H.

 

[George Herold]

On Feb 21, 8:11 am, JW <n...@dev.null> wrote:

On Mon, 20 Feb 2012 08:46:38 -0800 (PST) George Herold
gher...@teachspin.com> wrote in Message id:
db84ada7-d3a7-4673-8067-71e6e02ac...@l16g2000vbl.googlegroups.com>:





On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around?  Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor.  And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light.  I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something.  With a
breadboard, it costs very little to try.  If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was.  (I'll have to do some testing, when I have
time.)

Try using some heat-shrink tubing, then pinch the ends closed while still
hot.- Hide quoted text -

- Show quoted text -

OK I can look at that too.

George H.

 

[George Herold]

On Feb 21, 9:29 am, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:

JW wrote:

On Mon, 20 Feb 2012 08:46:38 -0800 (PST) George Herold
gher...@teachspin.com> wrote in Message id:
db84ada7-d3a7-4673-8067-71e6e02ac...@l16g2000vbl.googlegroups.com>:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around?  Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor.  And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light.  I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something.  With a
breadboard, it costs very little to try.  If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was.  (I'll have to do some testing, when I have
time.)

Try using some heat-shrink tubing, then pinch the ends closed while still
hot.

Carbon paint is pretty good, e.g. ultraflat black Krylon.  It's somewhat
electrically conductive, though, so you have to be careful with it.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -

I use to paint Aquadag on the radiation baffles in the pumping lines
of low temperature probes.

George H.

 

[Phil Hobbs]

George Herold wrote:

On Feb 21, 9:29 am, Phil Hobbs
pcdhSpamMeSensel...@electrooptical.net> wrote:
JW wrote:

On Mon, 20 Feb 2012 08:46:38 -0800 (PST) George Herold
gher...@teachspin.com> wrote in Message id:
db84ada7-d3a7-4673-8067-71e6e02ac...@l16g2000vbl.googlegroups.com>:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around? Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor. And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light. I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something. With a
breadboard, it costs very little to try. If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was. (I'll have to do some testing, when I have
time.)

Try using some heat-shrink tubing, then pinch the ends closed while still
hot.

Carbon paint is pretty good, e.g. ultraflat black Krylon. It's somewhat
electrically conductive, though, so you have to be careful with it.



- Show quoted text -

I use to paint Aquadag on the radiation baffles in the pumping lines
of low temperature probes.

George H.

Hmm, interesting, I'd have thought you'd get a lot of outgassing even
from dried DAG, just on account of all that surface area.

And you weren't worried about flakes of DAG getting into the turbo? Or
was it diffusion-pumped?

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

 

[Phil Hobbs]

etpm@whidbey.com wrote:

On Tue, 21 Feb 2012 09:29:16 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

JW wrote:

On Mon, 20 Feb 2012 08:46:38 -0800 (PST) George Herold
gherold@teachspin.com> wrote in Message id:
db84ada7-d3a7-4673-8067-71e6e02ac4f6@l16g2000vbl.googlegroups.com>:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around? Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor. And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light. I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something. With a
breadboard, it costs very little to try. If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was. (I'll have to do some testing, when I have
time.)

Try using some heat-shrink tubing, then pinch the ends closed while still
hot.

Carbon paint is pretty good, e.g. ultraflat black Krylon. It's somewhat
electrically conductive, though, so you have to be careful with it.

Cheers

Phil Hobbs
So use black paint for white noise?
Eric

Absolutely. Use it and like it.

Cheers

Phil Hobbs

 

[George Herold]

On Feb 21, 11:39 am, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:

George Herold wrote:

On Feb 21, 9:29 am, Phil Hobbs
pcdhSpamMeSensel...@electrooptical.net> wrote:
JW wrote:

On Mon, 20 Feb 2012 08:46:38 -0800 (PST) George Herold
gher...@teachspin.com> wrote in Message id:
db84ada7-d3a7-4673-8067-71e6e02ac...@l16g2000vbl.googlegroups.com>:

On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around?  Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor.  And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light.  I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something..  With a
breadboard, it costs very little to try.  If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was.  (I'll have to do some testing, when I have
time.)

Try using some heat-shrink tubing, then pinch the ends closed while still
hot.

Carbon paint is pretty good, e.g. ultraflat black Krylon.  It's somewhat
electrically conductive, though, so you have to be careful with it.

- Show quoted text -

I use to paint Aquadag on the radiation baffles in the pumping lines
of low temperature probes.

George H.

Hmm, interesting, I'd have thought you'd get a lot of outgassing even
from dried DAG, just on account of all that surface area.

And you weren't worried about flakes of DAG getting into the turbo?  Or
was it diffusion-pumped?

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -

No this was in the big ass pumping lines.... Mechanical pumps. going
down into a He4 pot. Some piece of low temperature lore said to use
aquadag.. and I just followed that advice, no idea how much it reduced
the heat load. If at all.

George H.

 

[Phil Hobbs]

George Herold wrote:

On Feb 21, 8:11 am, JW <n...@dev.null> wrote:
On Mon, 20 Feb 2012 08:46:38 -0800 (PST) George Herold
gher...@teachspin.com> wrote in Message id:
db84ada7-d3a7-4673-8067-71e6e02ac...@l16g2000vbl.googlegroups.com>:





On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around? Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor. And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light. I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something. With a
breadboard, it costs very little to try. If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was. (I'll have to do some testing, when I have
time.)

Try using some heat-shrink tubing, then pinch the ends closed while still
hot.- Hide quoted text -

- Show quoted text -

Black electrical tape.

3M Scotch Super 33+ Vinyl electrical tape made in USA (2007)

I’m also posting this on sci.optics too. (So a bit of a recap)

So I was testing a noise source made with some glass encapsulated
Zener diodes (1N5250). The Zeners are wrapped in the above electrical
tape to keep out the light. I found that light was still leaking in.
(The noise amplitude goes down dramatically when exposed to
light.)

I tried to measure the transmission of the above tape with a Si PIN
photodiode.
I first used a diode laser at 780 nm. The laser was producing a bit
more than 10mW of power (8mA of photo current) and I could see no
signal leaking through one layer of tape (PD gain = 10Meg ohm, DC
offset = 0.1 mV.. no change at 10uV level.)

I then put the same photodiode under a 60 Watt incandescent lamp.
Which when stuck right in front of the PD produced about 2.5mA of
photo-current. Again with the tape, at the highest gain setting I
could see no change at the 10uV level.

10uV/ 10 M ohm, about 1pA of current vs a few mA’s. Attenuation of at
least10^9!

I’m stuck wondering what the heck is going on?
Is the Zener also a ‘very’ sensitive photodetector?
Or does it respond to some longer wavelength photons than the Si
photodiode that is leaking through the tape?

The PD is a square about 0.25” on a side (0.0625 sq. in area).
It’s a bit hard to know the zener active area. Looking under a
microscope there’s gap about 0.01” (inches) between copper colored
electrodes. Maybe 0.06” wide, so an area of maybe 6x10^-4 sq in.

George (confused again) Herold

That suggests that it isn't photocurrent, all right. Could it be pickup
from an electronic ballast? Does putting aluminum foil over the tape
help?

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

 

[George Herold]

On Feb 21, 8:11 am, JW <n...@dev.null> wrote:

On Mon, 20 Feb 2012 08:46:38 -0800 (PST) George Herold
gher...@teachspin.com> wrote in Message id:
db84ada7-d3a7-4673-8067-71e6e02ac...@l16g2000vbl.googlegroups.com>:





On Feb 19, 12:07 am, Michael Black <et...@ncf.ca> wrote:
On Sat, 18 Feb 2012, k...@att.bizzzzzzzzzzzz wrote:
Has anybody tried LEDs as noise sources ?

Wouldn't there be correlation problems with any light sources around?  Seems
like it's needlessly asking for trouble.

Yes, and someone's already warned about that, but the issue isn't because
of it's an LED but because of the seethrough casing.

I remember one article about a VCO where the author suggested trying
different types of diodes for the varactor.  And he mentioned trying some
small signal diodes and having AC hum on the output, until he realized the
hum was coming from the desk lamp that was shining on the clear-cased
diode.

I've seen other mentions of problems because of light.  I recall one
article warning about it, but not because of hum, but because the external
light was affecting diodes, and they were biased wrong or something, or
maybe turning on when they shouldn't.

Since LEDs have been used as low voltage zeners, perhaps they do have some
ability to better generate noise at a lower voltage or something.  With a
breadboard, it costs very little to try.  If it works, simply paint the
LED, get rid of any external problem.

What are you going to paint it with?

I discovered over the weekend, that black electrical tape is not as
good as I thought it was.  (I'll have to do some testing, when I have
time.)

Try using some heat-shrink tubing, then pinch the ends closed while still
hot.- Hide quoted text -

- Show quoted text -

Black electrical tape.

3M Scotch Super 33+ Vinyl electrical tape made in USA (2007)

I’m also posting this on sci.optics too. (So a bit of a recap)

So I was testing a noise source made with some glass encapsulated
Zener diodes (1N5250). The Zeners are wrapped in the above electrical
tape to keep out the light. I found that light was still leaking in.
(The noise amplitude goes down dramatically when exposed to
light.)

I tried to measure the transmission of the above tape with a Si PIN
photodiode.
I first used a diode laser at 780 nm. The laser was producing a bit
more than 10mW of power (8mA of photo current) and I could see no
signal leaking through one layer of tape (PD gain = 10Meg ohm, DC
offset = 0.1 mV.. no change at 10uV level.)

I then put the same photodiode under a 60 Watt incandescent lamp.
Which when stuck right in front of the PD produced about 2.5mA of
photo-current. Again with the tape, at the highest gain setting I
could see no change at the 10uV level.

10uV/ 10 M ohm, about 1pA of current vs a few mA’s. Attenuation of at
least10^9!

I’m stuck wondering what the heck is going on?
Is the Zener also a ‘very’ sensitive photodetector?
Or does it respond to some longer wavelength photons than the Si
photodiode that is leaking through the tape?

The PD is a square about 0.25” on a side (0.0625 sq. in area).
It’s a bit hard to know the zener active area. Looking under a
microscope there’s gap about 0.01” (inches) between copper colored
electrodes. Maybe 0.06” wide, so an area of maybe 6x10^-4 sq in.

George (confused again) Herold