Thanks Hal, and Henry, I was wondering about how they acted. I have really
nver studied them that much for this type of application. Of course, I have
some old moon filters laying around, that are a very low shade, and I could
cut up. That could work without having to play with the LED's.
Thanks,
There get slower with falling current.
- Henry
--
ehydra.dyndns.info
Hal Murray schrieb:
I was thinking about trying an orange or yellow LED here, and dimming the
LED with the series resistor, trying to make it as dim as the neon bulb, but
I don't know if a LED can be dimmed down that low.
> I was thinking about trying an orange or yellow LED here, and dimming the
> LED with the series resistor, trying to make it as dim as the neon bulb, but
> I don't know if a LED can be dimmed down that low.
LEDs work fine at low output levels. At low current, the light output is
linear with cu
> John,
>
> They used Lucite rods, I shouldn't have said tubes. The neon bulbs are
> about at the center of the PC board, and the CDS cells are at the edge, so
> to get the light to them, they used the rods.
More than that. They wanted to minimize capacitance coupled between the
neons and cells to
Paul,
No, not the direct light emitted from the LED, but the extra current the
cell passed was probably over their limit. I thought of placing the LED's
vertical to the Lucite rods, instead of horizontal, or head-on, to decrease
the intensity. From the side, a LED, it's much dimmer. The NE-3 bulbs
In message <201106151021530546.2070a...@smtp.citynet.net>, "Will Matney" writes
:
>My guess is that the LED's brightness helped kill the CDS cells.
That is not possible by direct effect, light does not hurt CDS cells.
It is far more likely that more intense light than designed has decreased
the
John,
They used Lucite rods, I shouldn't have said tubes. The neon bulbs are
about at the center of the PC board, and the CDS cells are at the edge, so
to get the light to them, they used the rods. I think they did the same
thing on the 845AB too, but I'm not looking at the manual right now to see
> John,
>
> I will check it out, and may do some experiments myself on these. Also, I
> will take a look at the photo-FET's, as I had forgotten about those.
>
> What has me wondering is how neon bulbs act in the circuit, their low
> brightness, and their drop out times, as I think the on voltage is
Well a couple of thoughts.
As I said modern choppers do work and have big pluses these days.
But to the neon bulb.
I would use a led thats color more approximates neon. They make them.
I rebuilt a HP5360 counter /nixie with modern 7 seg leds that matched the
nixie color and it turned out very well.
Bruce,
Correct, and by adding the series resistor for higher impedance, the
voltage regulation at the zener value is raised from 10 volts to some value
higher. I actually remember a variable bias control to a tube using a
similar circuit, except the fixed resistor was a pot. He shows using this
on
Will Matney wrote:
As far as the power supply is concerned, I think I am going to go with
Ni-Cad batteries, and regulate the voltages. I think what they had was
nothing more than four step voltages from the battery supply, going from 3,
6 (7), 12, and 24 Vdc, or X2 of the other. From what I saw i
John,
I will check it out, and may do some experiments myself on these. Also, I
will take a look at the photo-FET's, as I had forgotten about those.
What has me wondering is how neon bulbs act in the circuit, their low
brightness, and their drop out times, as I think the on voltage is around
90 v
Paul,
Remember the HP 412? It used incandescent bulbs, a spinning disc, and a
syncronous motor. I actually still use two of these, and the bulbs are the
only fault.
Getting back on topic, somewhat, has anyone ever checked the noise on the
rails feeding the OCXO's in this GPS equipment? Especially
Paul,
Remember the HP 412? It used incandescent bulbs, a spinning disc, and a
syncronous motor. I actually still use two of these, and the bulbs are the
only fault.
Best,
Will
*** REPLY SEPARATOR ***
On 6/14/2011 at 10:21 PM paul swed wrote:
>Though its a bit off topic
>Ran i
Hi Will,
I don't know. Check the HP Group archives. I only vaguely followed the
thread. I'm not so sure a phototransistor will work without circuit mods.
A photoFET might.
Best,
-John
===
> John,
>
> I wondered about that, as using a LED is generally in conjunction with a
> photo-
John,
I wondered about that, as using a LED is generally in conjunction with a
photo-transistor, and not a CDS cell. The reason I thought it might work is
that a company years back used them together to form a safety light
curtain.
The Fluke, and the HP, had a bad rep for those neon bulbs going o
Though its a bit off topic
Ran into this chopper issue also on a HP410. I replaced the thing with a
modern chopper amp. I think an LTC. This was quite a few years ago (10 plus
easily) and it works very well. Still does actually. It did take a bit of
rework to get things back in balance correctly.
I forgot to add that noise on the bridge excitation should not matter much
when the bridge is at null, as the differential mode voltage is zero.
-John
===
> John,
>
> No, it's DC. I'm trying to meet the original specs of the batteries in not
> only voltage/current, but cleanliness o
The reason I asked is that most microvolt bridges use choppers and have BP
filters at the chopper frequency, so noise is largely uncorrelated.
On the neon photochoppers, it has been discussed at length several times
on the HP-Agilent Yahyoo Group. A similar thing is used in the 410C. There
are app
John,
No, it's DC. I'm trying to meet the original specs of the batteries in not
only voltage/current, but cleanliness of the current.
Now inside the Fluke 844, it has a chopper, and it uses an AC power supply
internally to feed its circuitry. The Vishays bridge uses the batteries
voltage, and on
Is the bridge excitation AC or DC. If it's AC, you may not even need
low-noise power supplies.
-John
==
> Hi Will,
>
> You could consider building your own power supply system for the
> replacement of
> the batteries. Use a separate power transformer which, I suspect, would
> be s
Bill,
I forgot to add, the Vishay bridge uses a Fluke 844 (OEM version of the
845AB) null-microvolt meter to read the bridge circuit. ESI did the same
thing, first using a HP 419, and then a Keithly 155 OEM meter assembly, for
their bridges.
The Fluke has its own supply from the line voltage. The
Hi Will,
You could consider building your own power supply system for the replacement of
the batteries. Use a separate power transformer which, I suspect, would be
small
as the current requirements would be low for driving a bridge circuit.
The main company to look toward for high quality, low
Bob,
Yes, and especially after reading the article that Chris posted the link
to, I agree. Definately the lead-acid is out, after I saw the noise the
battery alone could generate. I always thought they were much cleaner than
that, and I wonder what type of havoc that could create on a GPS device i
Hi
Ni-cads are pretty low noise, reasonably stable, and close to the per cell
voltage of the mercury cells. The gotcha is the self discharge rate. If you
don't need a floating supply I suspect you can build up a " good enough" linear
regulator to get things working.
Bob
On Jun 14, 2011, at
Bob,
I've thought about that, and also thought about the 24 volt battery packs
used in those Schwinn scooters the kids have. I can buy a 24 volt charger
cheap for those, but the batteries run about $60.00 each plus shipping, and
they are probably rated at around 4 amp hours, I think. It may be the
Chirs,
No, actually, I need both. They used the mercury battery over its ability
to hold the voltage steady over its charged cycle, which was something they
did pretty well. It's a shame they've really not made anything to match
them yet, except I've heard of folks using Lithium in their place. I
Hi
Ni-cads are a pretty good bet.
Bob
On Jun 14, 2011, at 7:02 PM, "Will Matney" wrote:
> Hello,
>
> I am in need of a very clean 24 Vdc power source, to replace some old
> mercury cell batteries with. What would a good low noise, clean, power
> supply be in your recommendations? I thought
I was just looking at battery noise last week. I assume you need low
noise, not good regulation. If so then in practical terms, I think the
best thing you could do is get an 8 cell battery holder for AA cells
then connect a 220 uF capacitor across it.
This is pretty good. has test results for se
Hello,
I am in need of a very clean 24 Vdc power source, to replace some old
mercury cell batteries with. What would a good low noise, clean, power
supply be in your recommendations? I thought of using two 12 Vdc lead-acid
batteries in series, and making a charging circuit with regulators, but I
a
30 matches
Mail list logo
