[volt-nuts] Finally got around to modifying my Fluke 845ab with LED's

[Dallas Smith]

Thank you Robert for you experience,

  My white LED's did have a persistence to them, so I'm going to change 
them to ORG/RED (615nm). I've temporarily using some low output amber 
LED's and determined that the caps I changed needed to be changed back 
to original values. I also modified the zero control circuit with a 1.25 
volt reference centered at zero with two switching diodes to base the 
offset at zero for less drift. I,m considering using the Linear chopper 
amp Randy's using. But I'm not sure how to incorporate the gain control 
at S101B? The over all feedback should be no problem.

Dallas


On 9/15/2014 3:57 PM, George Atkinson wrote:
> Hi,
> I'm late to this thread, but have some experience. Several years ago I did
> some research on replacing xenon flashlamps in a high speed fluorescence
> instrument application. As the white LED candidates had phosphor coatings I
> assumed (don't assume - guess ;-) that they would be too slow. It turned
> out that they were significantly faster than the xenon lamps, with sharp
> turn-off rather than the tail of the flashlamp.
> So don't dismiss white LEDs for modulated applications.
>
> Robert G8RPI.
>
> On 11 September 2014 13:14, Chuck Harris <cfharris at erols.com> wrote:
>
>> Hi Dallas,
>>
>> Let us know if it helps.  Neons are very fast light sources, and
>> can switch way faster than the CdS photo resistors can respond.
>>
>> A nice red/orange LED should work well with the original CdS
>> photo resistors.
>>
>> -Chuck Harris
>>
>>
>> Dallas Smith wrote:
>>
>>> Chuck,
>>>
>>> After searching for the wave length of NE2 neon bulbs, I found that the
>>> spectrum is
>>> between 600-650nm. So I ordered red-org at 615nm. The white LED's I've
>>> have do have
>>> the characteristics you mentioned, Thank you for all your input, maybe
>>> the results
>>> will show some improvement.
>>>
>>> Dallas
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