On Monday, January 18, 2016 11:45:00 AM Poul-Henning Kamp wrote:

Actually when forward biased they are not that sensitive.
I used a string of forward biased LEDS to set the voltage of a node in an
amplifier. To detect 100Hz modulation due to photocurrents in the LEDs the 150W
incandescent bulb had to be placed within a few cm of the LEDs.
Using a little bit of opaque pain or epoxy is a small price to pay.
Photosensitivity is also an issue with glass encapsulated low leakage diodes
if you scratch  the paint.
Even glass encapsulated reference (and other) zeners are photosensitive.
For sensitive measurements a light tight enclosure is often used.

Bruce

In message 29659871.S9XTlaFu4r@linux, Bruce Griffiths writes:

Incandescent bulbs don't have much "hum" in their light output,
they're basically heating elements and they don't cool down nearly
fast enough.

Try with fluorescent light instead, there's a reason people accuse
them of flickering.

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

Hi,

No, the black plastic around ICs isn't black by chance.
Einstein got his Nobel price on the photoelectric effect, which is
relevant in this case.

A few years ago I assisted in modifying a camera for an amateur
astronomer. Among the modifications, one was to turn of power for a
pre-amplifier, as the biased amplifier was also emitting a faint
infrared light that the sensor picked up and accumulated causing a
redish gradient over the whole screen - mathcing the radiation pattern
from the on-chip amplifier. By only powering on the amplifier before
read-out significantly reduced the effect to essentially zero.

Cheers,
Magnus

On 01/18/2016 04:11 PM, Bob Camp wrote:

Hi

Some time - check out what a “60 Hz” incandescent bulb looks like when
hooked to 20 Hz …. flicker flicker flicker …

I suspect they optimize the thermal mass of the filament to reduce the flicker at
50/60 Hz.

Bob

On Mon, 18 Jan 2016 20:45:20 +0000, you wrote:

Hook photocell to an audio amp and shine a 60Hz powered lamp on it; you'll
be surprised.  I don't know what the modulation percentage is, but I know a
flashlight lamp can be modulated with decent sounding speech audio.

--
Gary Woods AKA K2AHC- PGP key on request, or at home.earthlink.net/~garygarlic
Zone 5/4 in upstate New York, 1420' elevation. NY WO G

On Monday, January 18, 2016 08:45:20 PM you wrote:

150W

Its actually quite difficult to find low frequency operated fluorescent lamps
here. I only have a small 6" one (sans phosphor so strictly not fluorescent)
I assembled some years ago as a source of the mercury green line for an
interferometer. I'll unearth it and setup an experiment using forward
biased LEDs.

In any case obtaining an LED photocurrent of more than few microamp is
very difficult. With a forward current of a few mA the resultant change in
LED voltage will only be a few uV.

Shielding the LED to  ensure that such photocurrent induced modulation
of the forward voltage drop is at the subnanovolt level is relatively simple.

I used to test the suitability of photomultiplier housings by checking for
light leaks with a 1 KW incandescent lamp using the photomultiplier as the
light detector. Labyrinth seals with nested enclosures with everything
painted matte black usually sufficed.

Biggest problem was light leakage via the BNC/MHV connectors.

Bruce

On 1/18/16 4:19 PM, Bob Camp wrote:

They optimize that to a tiny fraction of a gnat's eylash.  Mass
production, every microcent counts.

That true. Its nice looking "Timeng report". I saw the numbers there.

Performance Summary for Xilinx XC32C32A:

Min. Clock Period 3.300 ns.
Max. Clock Frequency (fSYSTEM) 303.030 MHz.

Clock to Setup (tCYC) 3.300 ns.
Clock Pad to Output Pad Delay (tCO) 3.700 ns.

Its always few nanoseconds delays. Which quite sad, since I was expect
better from CPLD. With this "background", PICDIV looks much more
attractive with its 2ps Jitter.
Long live for Tom and Microchip engineers !

D flip-flop looks like a good solution. However, now I am thinking it
could do its own "timing correction" (skew/delay) to the signal. Looks
like "classic" 74LS74 has similar delays as CPLD has.
Nothing is perfect. ;-)

I was using Wenzel "two 3906" solution. BTW, when I compare it to
"74AC", I saw more spikes with it:

http://www.patoka.ca/OCXO/Vectron-74AC04b-2-OSQ.png
http://www.patoka.ca/OCXO/Vectron-74AC04-2-OSQ.png

Which make me thinking that 74AC/74HC logic make the conversion more
"smooth". However, in my observations, I saw that "two 3906" is close to
reflect the actual signal coming from OCXO. I mean if OCXO has some
spike (noise), than it immediately will be noticed by "two 3906" schema.
74AC/74HC solution somehow remove/ignore it. I don't know how to explain
this. Its just from my setup and my observation and probably not correct
at all.

--
WBW,

V.P.

The clock to output delay of the PIC will be similar or perhaps a little
worse.
You seem to be confusing delay and jitter.
There are zero delay buffers (in the sense that the output transitions are
aligned with the clock transitions) but these have excessive jitter due to the
internal DLL used to achieve 'zero delay'.

Bruce

On Tuesday, January 19, 2016 03:37:13 PM Vlad wrote:

Hi

If you fire up the FPGA and measure it, you will find a sub picosecond jitter on a signal passing through it.
If you use the internal PLL or DLL in an FPGA, you might indeed see close to 1x10^-12 ADEV in some cases.
In general you should be able to get into the parts in the 10^-13 range even with an internal FPGA PLL.

Delay wise, you have the advantage on the FPGA that the “internal” gates are running 100’s of ps delay wise
rather than a couple of ns delay. You still have i/o delay and routing delay to deal with. As mentioned in another
post, delay is very much not the same thing as jitter.

Bob