[time-nuts] FE-5680A Loop Lock Indicator

[Hal Murray]

bob at evoria.net said:
> Is 3ma really that big a deal?  I know squat about CMOS gates.  I guess it
> is pulling the voltage down by 25%, though. 

There should be something in the data sheet.  1/2 :)

If you trace the signal back the next time you have it open, you might be 
able to figure out which data sheet to go looking for.

For things like 5V CMOS signals, HC is a reasonable guess.  If you look at 
the data sheet for a typical HC chip, it will specify Voh at a load current 
of 20 uA and 4 mA.  That at least tells you that a 4 mA load is sensible.

I'd probably use 10K because my junk box has lots of 1K and 10K, and 1K seems 
too small.

10K at 5V is 1/2 mA max or 1/4 mA if the output droops and we deduct some 
more for Vbe.  How bright do you want your LED to be?  (How much current?)  
Scan the data sheet and look for minimum Beta...

Plan B:
  Insert a PIC/AVR/whatever-you-like.  It can turn on a green LED for OK, and 
blink a red LED for non-locked.  And the data sheet will tell you how much 
current you can drive.



-- 
These are my opinions.  I hate spam.